android 4.4 batteryservice 电池电量显示分析

最近工作接触到这么的东西，这是我对整个电池管理方面Java 层的分析。如果想了解底层的话，请看我的博客：
android 4.4 电池电量管理底层分析(C\C++层) （http://blog.csdn.NET/daweibalang717/article/details/41446993）
先贴一张类与类之间的关系图：

    Android开机过程中会加载系统BatteryService ,说一下电池电量相关的,本文主要讲述关于JAVA 层代码。文件路径：\frameworks\base\services\java\com\android\server\BatteryService.java   下面贴出源码。我把注释加上。个人理解，仅参考。

[java] view plaincopy
/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.server;

import android.os.BatteryStats;
import com.android.internal.app.IBatteryStats;
import com.android.server.am.BatteryStatsService;

import android.app.ActivityManagerNative;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.BatteryManager;
import android.os.BatteryProperties;
import android.os.Binder;
import android.os.FileUtils;
import android.os.Handler;
import android.os.IBatteryPropertiesListener;
import android.os.IBatteryPropertiesRegistrar;
import android.os.IBinder;
import android.os.DropBoxManager;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.os.SystemClock;
import android.os.UEventObserver;
import android.os.UserHandle;
import android.provider.Settings;
import android.util.EventLog;
import android.util.Slog;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;


/**
*

BatteryService monitors the charging status, and charge level of the device
* battery. When these values change this service broadcasts the new values
* to all {@link android.content.BroadcastReceiver IntentReceivers} that are
* watching the {@link android.content.Intent#ACTION_BATTERY_CHANGED
* BATTERY_CHANGED} action.

The new values are stored in the Intent data and can be retrieved by
* calling {@link android.content.Intent#getExtra Intent.getExtra} with the
* following keys:

"scale" - int, the maximum value for the charge level

"level" - int, charge level, from 0 through "scale" inclusive

"status" - String, the current charging status.
*

"health" - String, the current battery health.
*

"present" - boolean, true if the battery is present
*

"icon-small" - int, suggested small icon to use for this state

"plugged" - int, 0 if the device is not plugged in; 1 if plugged
* into an AC power adapter; 2 if plugged in via USB.

"voltage" - int, current battery voltage in millivolts

"temperature" - int, current battery temperature in tenths of
* a degree Centigrade

"technology" - String, the type of battery installed, e.g. "Li-ion"

*
*

* The battery service may be called by the power manager while holding its locks so
* we take care to post all outcalls into the activity manager to a handler.
*
* FIXME: Ideally the power manager would perform all of its calls into the battery
* service asynchronously itself.
*

*/
public final class BatteryService extends Binder {
    private static final String TAG = BatteryService.class.getSimpleName();

    private static final boolean DEBUG = false;

    private static final int BATTERY_SCALE = 100;    // battery capacity is a percentage

    // Used locally for determining when to make a last ditch effort to log
    // discharge stats before the device dies.
    private int mCriticalBatteryLevel;

    private static final int DUMP_MAX_LENGTH = 24 * 1024;
    private static final String[] DUMPSYS_ARGS = new String[] { "--checkin", "--unplugged" };

    private static final String DUMPSYS_DATA_PATH = "/data/system/";

    // This should probably be exposed in the API, though it's not critical
    private static final int BATTERY_PLUGGED_NONE = 0;

    private final Context mContext;
    private final IBatteryStats mBatteryStats;
    private final Handler mHandler;

    private final Object mLock = new Object();

    private BatteryProperties mBatteryProps;
    private boolean mBatteryLevelCritical;
    private int mLastBatteryStatus;
    private int mLastBatteryHealth;
    private boolean mLastBatteryPresent;
    private int mLastBatteryLevel;
    private int mLastBatteryVoltage;
    private int mLastBatteryTemperature;
    private boolean mLastBatteryLevelCritical;

    private int mInvalidCharger;
    private int mLastInvalidCharger;

    private int mLowBatteryWarningLevel;
    private int mLowBatteryCloseWarningLevel;
    private int mShutdownBatteryTemperature;

    private int mPlugType;
    private int mLastPlugType = -1; // Extra state so we can detect first run

    private long mDischargeStartTime;
    private int mDischargeStartLevel;

    private boolean mUpdatesStopped;

    private Led mLed;

    private boolean mSentLowBatteryBroadcast = false;

    private BatteryListener mBatteryPropertiesListener;
    private IBatteryPropertiesRegistrar mBatteryPropertiesRegistrar;
//构造函数
    public BatteryService(Context context, LightsService lights) {
        mContext = context;
        mHandler = new Handler(true /*async*/);
        mLed = new Led(context, lights);//这个应该是指示灯，没实验
        mBatteryStats = BatteryStatsService.getService();

//低电量临界值，这个数我看的源码版本值是4（在这个类里只是用来写日志）
        mCriticalBatteryLevel = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_criticalBatteryWarningLevel);

//低电量告警值，值15，下面会根据这个变量发送低电量的广播Intent.ACTION_BATTERY_LOW（这个跟系统低电量提醒没关系，只是发出去了）
        mLowBatteryWarningLevel = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_lowBatteryWarningLevel);

//电量告警取消值，值20 ，就是手机电量大于等于20的话发送Intent.ACTION_BATTERY_OKAY
        mLowBatteryCloseWarningLevel = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_lowBatteryCloseWarningLevel);

//值是680 ，温度过高，超过这个值就发送广播，跳转到将要关机提醒。
       mShutdownBatteryTemperature = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_shutdownBatteryTemperature);

        // watch for invalid charger messages if the invalid_charger switch exists
        if (new File("/sys/devices/virtual/switch/invalid_charger/state").exists()) {
            mInvalidChargerObserver.startObserving(
                    "DEVPATH=/devices/virtual/switch/invalid_charger");
        }
//电池监听，这个应该是注册到底层去了。当底层电量改变会调用此监听。然后执行update(BatteryProperties props)；
        mBatteryPropertiesListener = new BatteryListener();

        IBinder b = ServiceManager.getService("batterypropreg");
        mBatteryPropertiesRegistrar = IBatteryPropertiesRegistrar.Stub.asInterface(b);

        try {
//这里注册
          mBatteryPropertiesRegistrar.registerListener(mBatteryPropertiesListener);
        } catch (RemoteException e) {
            // Should never happen.
        }
    }
//开机后先去看看是否没电了或者温度太高了。如果是，就关机提示（关机提示我等会介绍）。
    void systemReady() {
        // check our power situation now that it is safe to display the shutdown dialog.
        synchronized (mLock) {
            shutdownIfNoPowerLocked();
            shutdownIfOverTempLocked();
        }
    }
//返回是否在充电，这个函数在PowerManagerService.java 中调用
    /**
     * Returns true if the device is plugged into any of the specified plug types.
     */
    public boolean isPowered(int plugTypeSet) {
        synchronized (mLock) {
            return isPoweredLocked(plugTypeSet);
        }
    }
//就是这里，通过充电器类型判断是否充电
    private boolean isPoweredLocked(int plugTypeSet) {
//我这英语小白猜着翻译下：就是开机后，电池状态不明了，那我们就认为就在充电，以便设备正常工作。
        // assume we are powered if battery state is unknown so
        // the "stay on while plugged in" option will work.
        if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_UNKNOWN) {
            return true;
        }
//充电器
        if ((plugTypeSet & BatteryManager.BATTERY_PLUGGED_AC) != 0 && mBatteryProps.chargerAcOnline) {
            return true;
        }
//USB，插电脑上充电
      if ((plugTypeSet & BatteryManager.BATTERY_PLUGGED_USB) != 0 && mBatteryProps.chargerUsbOnline) {
            return true;
        }
//电源是无线的。（我没见过...）
        if ((plugTypeSet & BatteryManager.BATTERY_PLUGGED_WIRELESS) != 0 && mBatteryProps.chargerWirelessOnline) {
            return true;
        }
        return false;
    }

    /**
     * Returns the current plug type.
     */
//充电器类型
   public int getPlugType() {
        synchronized (mLock) {
            return mPlugType;
        }
    }

    /**
     * Returns battery level as a percentage.
     */
//电池属性：电量等级（0-100）
    public int getBatteryLevel() {
        synchronized (mLock) {
            return mBatteryProps.batteryLevel;
        }
    }

    /**
     * Returns true if battery level is below the first warning threshold.
     */
//低电量
     public boolean isBatteryLow() {
        synchronized (mLock) {
            return mBatteryProps.batteryPresent && mBatteryProps.batteryLevel <= mLowBatteryWarningLevel;
        }
    }

    /**
     * Returns a non-zero value if an  unsupported charger is attached.
     */
//不支持的充电器类型
    public int getInvalidCharger() {
        synchronized (mLock) {
            return mInvalidCharger;
        }
    }

//这里就是没电了，要关机的提示。
    private void shutdownIfNoPowerLocked() {
        // shut down gracefully if our battery is critically low and we are not powered.
        // wait until the system has booted before attempting to display the shutdown dialog.
        if (mBatteryProps.batteryLevel == 0 && (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_DISCHARGING)) {
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    if (ActivityManagerNative.isSystemReady()) {
                        Intent intent = new Intent("android.intent.action.ACTION_REQUEST_SHUTDOWN_LOWBATTERY");//ACTION_REQUEST_SHUTDOWN
                        intent.putExtra(Intent.EXTRA_KEY_CONFIRM, false);
                        intent.putExtra("cant_be_cancel_by_button", true);
                        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                    }
                }
            });
        }
    }

//温度过高，关机提示（个人感觉这里有问题，温度过高为啥子跳转到没电关机提示界面）
    private void shutdownIfOverTempLocked() {
        // shut down gracefully if temperature is too high (> 68.0C by default)
        // wait until the system has booted before attempting to display the
        // shutdown dialog.
        if (mBatteryProps.batteryTemperature > mShutdownBatteryTemperature) {
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    if (ActivityManagerNative.isSystemReady()) {
                        Intent intent = new Intent("android.intent.action.ACTION_REQUEST_SHUTDOWN_LOWBATTERY");//ACTION_REQUEST_SHUTDOWN
                        intent.putExtra(Intent.EXTRA_KEY_CONFIRM, false);
                        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                    }
                }
            });
        }
    }
//这个方法就是被JNI回调的。用来更新上层状态的方法。
    private void update(BatteryProperties props) {
        synchronized (mLock) {
            if (!mUpdatesStopped) {
                mBatteryProps = props;
                // Process the new values.
                processValuesLocked();
            }
        }
    }
//嗯。这个就是最主要的方法了。
    private void processValuesLocked() {
        boolean logOutlier = false;
        long dischargeDuration = 0;

        mBatteryLevelCritical = (mBatteryProps.batteryLevel <= mCriticalBatteryLevel);
//充电器类型
       if (mBatteryProps.chargerAcOnline) {
            mPlugType = BatteryManager.BATTERY_PLUGGED_AC;
        } else if (mBatteryProps.chargerUsbOnline) {
            mPlugType = BatteryManager.BATTERY_PLUGGED_USB;
        } else if (mBatteryProps.chargerWirelessOnline) {
            mPlugType = BatteryManager.BATTERY_PLUGGED_WIRELESS;
        } else {
            mPlugType = BATTERY_PLUGGED_NONE;
        }

        if (DEBUG) {//日志，略过
            Slog.d(TAG, "Processing new values: "
                    + "chargerAcOnline=" + mBatteryProps.chargerAcOnline
                    + ", chargerUsbOnline=" + mBatteryProps.chargerUsbOnline
                    + ", chargerWirelessOnline=" + mBatteryProps.chargerWirelessOnline
                    + ", batteryStatus=" + mBatteryProps.batteryStatus
                    + ", batteryHealth=" + mBatteryProps.batteryHealth
                    + ", batteryPresent=" + mBatteryProps.batteryPresent
                    + ", batteryLevel=" + mBatteryProps.batteryLevel
                    + ", batteryTechnology=" + mBatteryProps.batteryTechnology
                    + ", batteryVoltage=" + mBatteryProps.batteryVoltage
                    + ", batteryCurrentNow=" + mBatteryProps.batteryCurrentNow
                    + ", batteryChargeCounter=" + mBatteryProps.batteryChargeCounter
                    + ", batteryTemperature=" + mBatteryProps.batteryTemperature
                    + ", mBatteryLevelCritical=" + mBatteryLevelCritical
                    + ", mPlugType=" + mPlugType);
        }

        // Let the battery stats keep track of the current level.
        try {
//把电池属性放到状态里面
           mBatteryStats.setBatteryState(mBatteryProps.batteryStatus, mBatteryProps.batteryHealth,
                    mPlugType, mBatteryProps.batteryLevel, mBatteryProps.batteryTemperature,
                    mBatteryProps.batteryVoltage);
        } catch (RemoteException e) {
            // Should never happen.
        }
//没电了
        shutdownIfNoPowerLocked();
//温度过高了
       shutdownIfOverTempLocked();

        if (mBatteryProps.batteryStatus != mLastBatteryStatus ||
                mBatteryProps.batteryHealth != mLastBatteryHealth ||
                mBatteryProps.batteryPresent != mLastBatteryPresent ||
                mBatteryProps.batteryLevel != mLastBatteryLevel ||
                mPlugType != mLastPlugType ||
                mBatteryProps.batteryVoltage != mLastBatteryVoltage ||
                mBatteryProps.batteryTemperature != mLastBatteryTemperature ||
                mInvalidCharger != mLastInvalidCharger) {

            if (mPlugType != mLastPlugType) {//当前充电器类型与上次的不一样
//并且上次充电器类型是no one ，那就可以知道，现在是插上充电器了。
               if (mLastPlugType == BATTERY_PLUGGED_NONE) {
                    // discharging -> charging

                    // There's no value in this data unless we've discharged at least once and the
                    // battery level has changed; so don't log until it does.
                    if (mDischargeStartTime != 0 && mDischargeStartLevel != mBatteryProps.batteryLevel) {
                        dischargeDuration = SystemClock.elapsedRealtime() - mDischargeStartTime;
                        logOutlier = true;
                        EventLog.writeEvent(EventLogTags.BATTERY_DISCHARGE, dischargeDuration,
                                mDischargeStartLevel, mBatteryProps.batteryLevel);
                        // make sure we see a discharge event before logging again
                        mDischargeStartTime = 0;
                    }
//并且本次充电器类型是no one ，那就可以知道，现在是拔掉充电器了。
                } else if (mPlugType == BATTERY_PLUGGED_NONE) {
                    // charging -> discharging or we just powered up
                    mDischargeStartTime = SystemClock.elapsedRealtime();
                    mDischargeStartLevel = mBatteryProps.batteryLevel;
                }
            }
            if (mBatteryProps.batteryStatus != mLastBatteryStatus ||//写日志，略过
                    mBatteryProps.batteryHealth != mLastBatteryHealth ||
                    mBatteryProps.batteryPresent != mLastBatteryPresent ||
                    mPlugType != mLastPlugType) {
                EventLog.writeEvent(EventLogTags.BATTERY_STATUS,
                        mBatteryProps.batteryStatus, mBatteryProps.batteryHealth, mBatteryProps.batteryPresent ? 1 : 0,
                        mPlugType, mBatteryProps.batteryTechnology);
            }
            if (mBatteryProps.batteryLevel != mLastBatteryLevel) {
                // Don't do this just from voltage or temperature changes, that is
                // too noisy.
                EventLog.writeEvent(EventLogTags.BATTERY_LEVEL,
                        mBatteryProps.batteryLevel, mBatteryProps.batteryVoltage, mBatteryProps.batteryTemperature);
            }
            if (mBatteryLevelCritical && !mLastBatteryLevelCritical &&
                    mPlugType == BATTERY_PLUGGED_NONE) {
                // We want to make sure we log discharge cycle outliers
                // if the battery is about to die.
                dischargeDuration = SystemClock.elapsedRealtime() - mDischargeStartTime;
                logOutlier = true;
            }
//本次调用，当前的充电状态
            final boolean plugged = mPlugType != BATTERY_PLUGGED_NONE;
//本次调用，上次调用的充电状态
            final boolean oldPlugged = mLastPlugType != BATTERY_PLUGGED_NONE;

            /* The ACTION_BATTERY_LOW broadcast is sent in these situations:
             * - is just un-plugged (previously was plugged) and battery level is
             *   less than or equal to WARNING, or
             * - is not plugged and battery level falls to WARNING boundary
             *   (becomes <= mLowBatteryWarningLevel).
             */
//用于发送低电量广播的判断
            final boolean sendBatteryLow = !plugged//（按sendBatteryLow = true 来说）当前没有充电
                    && mBatteryProps.batteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN//充电状态不是UNKNOWN
                    && mBatteryProps.batteryLevel <= mLowBatteryWarningLevel//当前电量小于告警值 15
                    && (oldPlugged || mLastBatteryLevel > mLowBatteryWarningLevel);//上次状态是充电或者上次电量等级大于告警值 15

            sendIntentLocked();//发送电池电量改变的广播Intent.ACTION_BATTERY_CHANGED

            // Separate broadcast is sent for power connected / not connected
            // since the standard intent will not wake any applications and some
            // applications may want to have smart behavior based on this.
            if (mPlugType != 0 && mLastPlugType == 0) {//插上充电器了
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        Intent statusIntent = new Intent(Intent.ACTION_POWER_CONNECTED);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            }
            else if (mPlugType == 0 && mLastPlugType != 0) {//断开充电器了
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        Intent statusIntent = new Intent(Intent.ACTION_POWER_DISCONNECTED);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            }
//发送低电量提醒（这个跟系统低电量提醒没关系，只是发出去了）
            if (sendBatteryLow) {
                mSentLowBatteryBroadcast = true;
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        Intent statusIntent = new Intent(Intent.ACTION_BATTERY_LOW);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            } else if (mSentLowBatteryBroadcast && mLastBatteryLevel >= mLowBatteryCloseWarningLevel) {//电量超过20了。电池状态OK了
                mSentLowBatteryBroadcast = false;
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        Intent statusIntent = new Intent(Intent.ACTION_BATTERY_OKAY);
                        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                        mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
                    }
                });
            }

            // Update the battery LED
            mLed.updateLightsLocked();

            // This needs to be done after sendIntent() so that we get the lastest battery stats.
            if (logOutlier && dischargeDuration != 0) {
                logOutlierLocked(dischargeDuration);
            }

            mLastBatteryStatus = mBatteryProps.batteryStatus;
            mLastBatteryHealth = mBatteryProps.batteryHealth;
            mLastBatteryPresent = mBatteryProps.batteryPresent;
            mLastBatteryLevel = mBatteryProps.batteryLevel;
            mLastPlugType = mPlugType;
            mLastBatteryVoltage = mBatteryProps.batteryVoltage;
            mLastBatteryTemperature = mBatteryProps.batteryTemperature;
            mLastBatteryLevelCritical = mBatteryLevelCritical;
            mLastInvalidCharger = mInvalidCharger;
        }
    }
//电池电量改变，把属性发出去（系统低电量提醒接收的是这个广播）
    private void sendIntentLocked() {
        //  Pack up the values and broadcast them to everyone
        final Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
                | Intent.FLAG_RECEIVER_REPLACE_PENDING);

        int icon = getIconLocked(mBatteryProps.batteryLevel);

        intent.putExtra(BatteryManager.EXTRA_STATUS, mBatteryProps.batteryStatus);
        intent.putExtra(BatteryManager.EXTRA_HEALTH, mBatteryProps.batteryHealth);
        intent.putExtra(BatteryManager.EXTRA_PRESENT, mBatteryProps.batteryPresent);
        intent.putExtra(BatteryManager.EXTRA_LEVEL, mBatteryProps.batteryLevel);
        intent.putExtra(BatteryManager.EXTRA_SCALE, BATTERY_SCALE);
        intent.putExtra(BatteryManager.EXTRA_ICON_SMALL, icon);
        intent.putExtra(BatteryManager.EXTRA_PLUGGED, mPlugType);
        intent.putExtra(BatteryManager.EXTRA_VOLTAGE, mBatteryProps.batteryVoltage);
        intent.putExtra(BatteryManager.EXTRA_TEMPERATURE, mBatteryProps.batteryTemperature);
        intent.putExtra(BatteryManager.EXTRA_TECHNOLOGY, mBatteryProps.batteryTechnology);
        intent.putExtra(BatteryManager.EXTRA_INVALID_CHARGER, mInvalidCharger);

        if (DEBUG) {
            Slog.d(TAG, "Sending ACTION_BATTERY_CHANGED.  level:" + mBatteryProps.batteryLevel +
                    ", scale:" + BATTERY_SCALE + ", status:" + mBatteryProps.batteryStatus +
                    ", health:" + mBatteryProps.batteryHealth +  ", present:" + mBatteryProps.batteryPresent +
                    ", voltage: " + mBatteryProps.batteryVoltage +
                    ", temperature: " + mBatteryProps.batteryTemperature +
                    ", technology: " + mBatteryProps.batteryTechnology +
                    ", AC powered:" + mBatteryProps.chargerAcOnline + ", USB powered:" + mBatteryProps.chargerUsbOnline +
                    ", Wireless powered:" + mBatteryProps.chargerWirelessOnline +
                    ", icon:" + icon  + ", invalid charger:" + mInvalidCharger);
        }

        mHandler.post(new Runnable() {
            @Override
            public void run() {
                ActivityManagerNative.broadcastStickyIntent(intent, null, UserHandle.USER_ALL);
            }
        });
    }

    private void logBatteryStatsLocked() {
        IBinder batteryInfoService = ServiceManager.getService(BatteryStats.SERVICE_NAME);
        if (batteryInfoService == null) return;

        DropBoxManager db = (DropBoxManager) mContext.getSystemService(Context.DROPBOX_SERVICE);
        if (db == null || !db.isTagEnabled("BATTERY_DISCHARGE_INFO")) return;

        File dumpFile = null;
        FileOutputStream dumpStream = null;
        try {
            // dump the service to a file
            dumpFile = new File(DUMPSYS_DATA_PATH + BatteryStats.SERVICE_NAME + ".dump");
            dumpStream = new FileOutputStream(dumpFile);
            batteryInfoService.dump(dumpStream.getFD(), DUMPSYS_ARGS);
            FileUtils.sync(dumpStream);

            // add dump file to drop box
            db.addFile("BATTERY_DISCHARGE_INFO", dumpFile, DropBoxManager.IS_TEXT);
        } catch (RemoteException e) {
            Slog.e(TAG, "failed to dump battery service", e);
        } catch (IOException e) {
            Slog.e(TAG, "failed to write dumpsys file", e);
        } finally {
            // make sure we clean up
            if (dumpStream != null) {
                try {
                    dumpStream.close();
                } catch (IOException e) {
                    Slog.e(TAG, "failed to close dumpsys output stream");
                }
            }
            if (dumpFile != null && !dumpFile.delete()) {
                Slog.e(TAG, "failed to delete temporary dumpsys file: "
                        + dumpFile.getAbsolutePath());
            }
        }
    }

    private void logOutlierLocked(long duration) {
        ContentResolver cr = mContext.getContentResolver();
        String dischargeThresholdString = Settings.Global.getString(cr,
                Settings.Global.BATTERY_DISCHARGE_THRESHOLD);
        String durationThresholdString = Settings.Global.getString(cr,
                Settings.Global.BATTERY_DISCHARGE_DURATION_THRESHOLD);

        if (dischargeThresholdString != null && durationThresholdString != null) {
            try {
                long durationThreshold = Long.parseLong(durationThresholdString);
                int dischargeThreshold = Integer.parseInt(dischargeThresholdString);
                if (duration <= durationThreshold &&
                        mDischargeStartLevel - mBatteryProps.batteryLevel >= dischargeThreshold) {
                    // If the discharge cycle is bad enough we want to know about it.
                    logBatteryStatsLocked();
                }
                if (DEBUG) Slog.v(TAG, "duration threshold: " + durationThreshold +
                        " discharge threshold: " + dischargeThreshold);
                if (DEBUG) Slog.v(TAG, "duration: " + duration + " discharge: " +
                        (mDischargeStartLevel - mBatteryProps.batteryLevel));
            } catch (NumberFormatException e) {
                Slog.e(TAG, "Invalid DischargeThresholds GService string: " +
                        durationThresholdString + " or " + dischargeThresholdString);
                return;
            }
        }
    }

    private int getIconLocked(int level) {
        if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_CHARGING) {
            return com.android.internal.R.drawable.stat_sys_battery_charge;
        } else if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_DISCHARGING) {
            return com.android.internal.R.drawable.stat_sys_battery;
        } else if (mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_NOT_CHARGING
                || mBatteryProps.batteryStatus == BatteryManager.BATTERY_STATUS_FULL) {
            if (isPoweredLocked(BatteryManager.BATTERY_PLUGGED_ANY)
                    && mBatteryProps.batteryLevel >= 100) {
                return com.android.internal.R.drawable.stat_sys_battery_charge;
            } else {
                return com.android.internal.R.drawable.stat_sys_battery;
            }
        } else {
            return com.android.internal.R.drawable.stat_sys_battery_unknown;
        }
    }

    @Override
    protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
        if (mContext.checkCallingOrSelfPermission(android.Manifest.permission.DUMP)
                != PackageManager.PERMISSION_GRANTED) {

            pw.println("Permission Denial: can't dump Battery service from from pid="
                    + Binder.getCallingPid()
                    + ", uid=" + Binder.getCallingUid());
            return;
        }

        synchronized (mLock) {
            if (args == null || args.length == 0 || "-a".equals(args[0])) {
                pw.println("Current Battery Service state:");
                if (mUpdatesStopped) {
                    pw.println("  (UPDATES STOPPED -- use 'reset' to restart)");
                }
                pw.println("  AC powered: " + mBatteryProps.chargerAcOnline);
                pw.println("  USB powered: " + mBatteryProps.chargerUsbOnline);
                pw.println("  Wireless powered: " + mBatteryProps.chargerWirelessOnline);
                pw.println("  status: " + mBatteryProps.batteryStatus);
                pw.println("  health: " + mBatteryProps.batteryHealth);
                pw.println("  present: " + mBatteryProps.batteryPresent);
                pw.println("  level: " + mBatteryProps.batteryLevel);
                pw.println("  scale: " + BATTERY_SCALE);
                pw.println("  voltage: " + mBatteryProps.batteryVoltage);

                if (mBatteryProps.batteryCurrentNow != Integer.MIN_VALUE) {
                    pw.println("  current now: " + mBatteryProps.batteryCurrentNow);
                }

                if (mBatteryProps.batteryChargeCounter != Integer.MIN_VALUE) {
                    pw.println("  charge counter: " + mBatteryProps.batteryChargeCounter);
                }

                pw.println("  temperature: " + mBatteryProps.batteryTemperature);
                pw.println("  technology: " + mBatteryProps.batteryTechnology);
            } else if (args.length == 3 && "set".equals(args[0])) {
                String key = args[1];
                String value = args[2];
                try {
                    boolean update = true;
                    if ("ac".equals(key)) {
                        mBatteryProps.chargerAcOnline = Integer.parseInt(value) != 0;
                    } else if ("usb".equals(key)) {
                        mBatteryProps.chargerUsbOnline = Integer.parseInt(value) != 0;
                    } else if ("wireless".equals(key)) {
                        mBatteryProps.chargerWirelessOnline = Integer.parseInt(value) != 0;
                    } else if ("status".equals(key)) {
                        mBatteryProps.batteryStatus = Integer.parseInt(value);
                    } else if ("level".equals(key)) {
                        mBatteryProps.batteryLevel = Integer.parseInt(value);
                    } else if ("invalid".equals(key)) {
                        mInvalidCharger = Integer.parseInt(value);
                    } else {
                        pw.println("Unknown set option: " + key);
                        update = false;
                    }
                    if (update) {
                        long ident = Binder.clearCallingIdentity();
                        try {
                            mUpdatesStopped = true;
                            processValuesLocked();
                        } finally {
                            Binder.restoreCallingIdentity(ident);
                        }
                    }
                } catch (NumberFormatException ex) {
                    pw.println("Bad value: " + value);
                }
            } else if (args.length == 1 && "reset".equals(args[0])) {
                long ident = Binder.clearCallingIdentity();
                try {
                    mUpdatesStopped = false;
                } finally {
                    Binder.restoreCallingIdentity(ident);
                }
            } else {
                pw.println("Dump current battery state, or:");
                pw.println("  set ac|usb|wireless|status|level|invalid ");
                pw.println("  reset");
            }
        }
    }

    private final UEventObserver mInvalidChargerObserver = new UEventObserver() {
        @Override
        public void onUEvent(UEventObserver.UEvent event) {
            final int invalidCharger = "1".equals(event.get("SWITCH_STATE")) ? 1 : 0;
            synchronized (mLock) {
                if (mInvalidCharger != invalidCharger) {
                    mInvalidCharger = invalidCharger;
                }
            }
        }
    };

    private final class Led {
        private final LightsService.Light mBatteryLight;

        private final int mBatteryLowARGB;
        private final int mBatteryMediumARGB;
        private final int mBatteryFullARGB;
        private final int mBatteryLedOn;
        private final int mBatteryLedOff;

        public Led(Context context, LightsService lights) {
            mBatteryLight = lights.getLight(LightsService.LIGHT_ID_BATTERY);

            mBatteryLowARGB = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryLowARGB);
            mBatteryMediumARGB = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryMediumARGB);
            mBatteryFullARGB = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryFullARGB);
            mBatteryLedOn = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryLedOn);
            mBatteryLedOff = context.getResources().getInteger(
                    com.android.internal.R.integer.config_notificationsBatteryLedOff);
        }

        /**
         * Synchronize on BatteryService.
         */
        public void updateLightsLocked() {
            final int level = mBatteryProps.batteryLevel;
            final int status = mBatteryProps.batteryStatus;
            if (level < mLowBatteryWarningLevel) {
                if (status == BatteryManager.BATTERY_STATUS_CHARGING) {
                    // Solid red when battery is charging
                    mBatteryLight.setColor(mBatteryLowARGB);
                } else {
                    // Flash red when battery is low and not charging
                    mBatteryLight.setFlashing(mBatteryLowARGB, LightsService.LIGHT_FLASH_TIMED,
                            mBatteryLedOn, mBatteryLedOff);
                }
            } else if (status == BatteryManager.BATTERY_STATUS_CHARGING
                    || status == BatteryManager.BATTERY_STATUS_FULL) {
                if (status == BatteryManager.BATTERY_STATUS_FULL || level >= 90) {
                    // Solid green when full or charging and nearly full
                    mBatteryLight.setColor(mBatteryFullARGB);
                } else {
                    // Solid orange when charging and halfway full
                    mBatteryLight.setColor(mBatteryMediumARGB);
                }
            } else {
                // No lights if not charging and not low
                mBatteryLight.turnOff();
            }
        }
    }

    private final class BatteryListener extends IBatteryPropertiesListener.Stub {
        public void batteryPropertiesChanged(BatteryProperties props) {
            BatteryService.this.update(props);
       }
    }
}
[java] view plain copy
/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.server;

import android.os.BatteryStats;
import com.android.internal.app.IBatteryStats;
import com.android.server.am.BatteryStatsService;

import android.app.ActivityManagerNative;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.BatteryManager;
import android.os.BatteryProperties;
import android.os.Binder;
import android.os.FileUtils;
import android.os.Handler;
import android.os.IBatteryPropertiesListener;
import android.os.IBatteryPropertiesRegistrar;
import android.os.IBinder;
import android.os.DropBoxManager;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.os.SystemClock;
import android.os.UEventObserver;
import android.os.UserHandle;
import android.provider.Settings;
import android.util.EventLog;
import android.util.Slog;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;


/**
*

The new values are stored in the Intent data and can be retrieved by
* calling {@link android.content.Intent#getExtra Intent.getExtra} with the
* following keys:

"scale" - int, the maximum value for the charge level

"level" - int, charge level, from 0 through "scale" inclusive

"status" - String, the current charging status.
*

"health" - String, the current battery health.
*

"present" - boolean, true if the battery is present
*

"icon-small" - int, suggested small icon to use for this state

"plugged" - int, 0 if the device is not plugged in; 1 if plugged
* into an AC power adapter; 2 if plugged in via USB.

"voltage" - int, current battery voltage in millivolts

"temperature" - int, current battery temperature in tenths of
* a degree Centigrade

"technology" - String, the type of battery installed, e.g. "Li-ion"

*
*

总结如下：此服务构造时会注册监听到系统JNI层。当电池电量改变的时候会调用update(BatteryProperties props) -----》processValuesLocked() 。而processValuesLocked() 函数会把电池状态把广播发送出去。其他类再接收广播进行处理
下一个类就是低电量提醒了，文件目录：\frameworks\base\packages\SystemUI\src\com\android\systemui\power\PowerUI.java
[java] view plaincopy
/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.systemui.power;

import android.app.AlertDialog;
import android.content.BroadcastReceiver;
import android.content.ContentResolver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.media.AudioManager;
import android.media.Ringtone;
import android.media.RingtoneManager;
import android.net.Uri;
import android.os.BatteryManager;
import android.os.Handler;
import android.os.PowerManager;
import android.os.SystemClock;
import android.os.UserHandle;
import android.provider.Settings;
import android.util.Slog;
import android.view.View;
import android.view.WindowManager;
import android.widget.TextView;

import com.android.systemui.R;
import com.android.systemui.SystemUI;

import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.util.Arrays;

public class PowerUI extends SystemUI { //总体说一下，这里才是处理低电量提醒的地方，他接收的广播是Intent.ACTION_BATTERY_CHANGED
    static final String TAG = "PowerUI";

    static final boolean DEBUG = false;

    Handler mHandler = new Handler();

    int mBatteryLevel = 100;
    int mBatteryStatus = BatteryManager.BATTERY_STATUS_UNKNOWN;
    int mPlugType = 0;
    int mInvalidCharger = 0;

    int mLowBatteryAlertCloseLevel;
    int[] mLowBatteryReminderLevels = new int[2];

    AlertDialog mInvalidChargerDialog;
    AlertDialog mLowBatteryDialog;
    TextView mBatteryLevelTextView;

    private long mScreenOffTime = -1;

    public void start() {  //这个类会在手机启动后，在SystemUI 里启动(就是系统界面)。

        mLowBatteryAlertCloseLevel = mContext.getResources().getInteger( //电量告警取消值，值20
                com.android.internal.R.integer.config_lowBatteryCloseWarningLevel);
        mLowBatteryReminderLevels[0] = mContext.getResources().getInteger( //低电量提醒 15
                com.android.internal.R.integer.config_lowBatteryWarningLevel);
        mLowBatteryReminderLevels[1] = mContext.getResources().getInteger( //低电量临界值 4
                com.android.internal.R.integer.config_criticalBatteryWarningLevel);

        final PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
        mScreenOffTime = pm.isScreenOn() ? -1 : SystemClock.elapsedRealtime();

        // Register for Intent broadcasts for...
        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_BATTERY_CHANGED);
        filter.addAction(Intent.ACTION_SCREEN_OFF);
        filter.addAction(Intent.ACTION_SCREEN_ON);
        mContext.registerReceiver(mIntentReceiver, filter, null, mHandler);
    }

    /**
     * Buckets the battery level.
     *
     * The code in this function is a little weird because I couldn't comprehend
     * the bucket going up when the battery level was going down. --joeo
     *
     * 1 means that the battery is "ok"
     * 0 means that the battery is between "ok" and what we should warn about.
     * less than 0 means that the battery is low
     */
    private int findBatteryLevelBucket(int level) {   //这个方法是用来警告判断用的。
        if (level >= mLowBatteryAlertCloseLevel) {
            return 1;
        }
        if (level >= mLowBatteryReminderLevels[0]) {
            return 0;
        }
        final int N = mLowBatteryReminderLevels.length;
        for (int i=N-1; i>=0; i--) {
            if (level <= mLowBatteryReminderLevels[i]) {
                return -1-i;
            }
        }
        throw new RuntimeException("not possible!");
    }

    private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() { //重点，广播接收处理
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (action.equals(Intent.ACTION_BATTERY_CHANGED)) {  //电池电量改变
                final int oldBatteryLevel = mBatteryLevel; //下边就是根据Intent获取BatteryService传过来的电池属性
                mBatteryLevel = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 100); /
                final int oldBatteryStatus = mBatteryStatus;
                mBatteryStatus = intent.getIntExtra(BatteryManager.EXTRA_STATUS,
                        BatteryManager.BATTERY_STATUS_UNKNOWN);
                final int oldPlugType = mPlugType;
                mPlugType = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, 1);
                final int oldInvalidCharger = mInvalidCharger;
                mInvalidCharger = intent.getIntExtra(BatteryManager.EXTRA_INVALID_CHARGER, 0);

                final boolean plugged = mPlugType != 0;
                final boolean oldPlugged = oldPlugType != 0;

                int oldBucket = findBatteryLevelBucket(oldBatteryLevel); //这两个值特别有意思，就是说记录下老的电量，记录一下新的电量，比较电量是增加了，还是减小了
                int bucket = findBatteryLevelBucket(mBatteryLevel);

                if (DEBUG) {
                    Slog.d(TAG, "buckets   ....." + mLowBatteryAlertCloseLevel
                            + " .. " + mLowBatteryReminderLevels[0]
                            + " .. " + mLowBatteryReminderLevels[1]);
                    Slog.d(TAG, "level          " + oldBatteryLevel + " --> " + mBatteryLevel);
                    Slog.d(TAG, "status         " + oldBatteryStatus + " --> " + mBatteryStatus);
                    Slog.d(TAG, "plugType       " + oldPlugType + " --> " + mPlugType);
                    Slog.d(TAG, "invalidCharger " + oldInvalidCharger + " --> " + mInvalidCharger);
                    Slog.d(TAG, "bucket         " + oldBucket + " --> " + bucket);
                    Slog.d(TAG, "plugged        " + oldPlugged + " --> " + plugged);
                }

                if (oldInvalidCharger == 0 && mInvalidCharger != 0) {
                    Slog.d(TAG, "showing invalid charger warning");
                    showInvalidChargerDialog(); //就是充电器不识别的弹窗
                    return;
                } else if (oldInvalidCharger != 0 && mInvalidCharger == 0) {
                    dismissInvalidChargerDialog();
                } else if (mInvalidChargerDialog != null) {
                    // if invalid charger is showing, don't show low battery
                    return;
                }

                if (!plugged
                        && (bucket < oldBucket || oldPlugged)
                        && mBatteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN
                        && bucket < 0) {
                    showLowBatteryWarning(); //这里哈，低电量提醒的弹窗

                    // only play SFX when the dialog comes up or the bucket changes
                    if (bucket != oldBucket || oldPlugged) {
                        playLowBatterySound();
                    }
                } else if (plugged || (bucket > oldBucket && bucket > 0)) { //插上充电器或者充电电池电量超过20取消弹窗
                    dismissLowBatteryWarning();
                } else if (mBatteryLevelTextView != null) {
                    showLowBatteryWarning();
                }
            } else if (Intent.ACTION_SCREEN_OFF.equals(action)) {
                mScreenOffTime = SystemClock.elapsedRealtime();
            } else if (Intent.ACTION_SCREEN_ON.equals(action)) {
                mScreenOffTime = -1;
            } else {
                Slog.w(TAG, "unknown intent: " + intent);
            }
        }
    };

    void dismissLowBatteryWarning() {
        if (mLowBatteryDialog != null) {
            Slog.i(TAG, "closing low battery warning: level=" + mBatteryLevel);
            mLowBatteryDialog.dismiss();
        }
    }

    void showLowBatteryWarning() {
        Slog.i(TAG,
                ((mBatteryLevelTextView == null) ? "showing" : "updating")
                + " low battery warning: level=" + mBatteryLevel
                + " [" + findBatteryLevelBucket(mBatteryLevel) + "]");

        CharSequence levelText = mContext.getString(
                R.string.battery_low_percent_format, mBatteryLevel);

        if (mBatteryLevelTextView != null) {
            mBatteryLevelTextView.setText(levelText);
        } else {
            View v = View.inflate(mContext, R.layout.battery_low, null);
            mBatteryLevelTextView = (TextView)v.findViewById(R.id.level_percent);

            mBatteryLevelTextView.setText(levelText);

            AlertDialog.Builder b = new AlertDialog.Builder(mContext);
                b.setCancelable(true);
                b.setTitle(R.string.battery_low_title);
                b.setView(v);
                b.setIconAttribute(android.R.attr.alertDialogIcon);
                b.setPositiveButton(android.R.string.ok, null);

            final Intent intent = new Intent(Intent.ACTION_POWER_USAGE_SUMMARY);
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                    | Intent.FLAG_ACTIVITY_MULTIPLE_TASK
                    | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS
                    | Intent.FLAG_ACTIVITY_NO_HISTORY);
            if (intent.resolveActivity(mContext.getPackageManager()) != null) {
                b.setNegativeButton(R.string.battery_low_why,
                        new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                        dismissLowBatteryWarning();
                    }
                });
            }

            AlertDialog d = b.create();
            d.setOnDismissListener(new DialogInterface.OnDismissListener() {
                    @Override
                    public void onDismiss(DialogInterface dialog) {
                        mLowBatteryDialog = null;
                        mBatteryLevelTextView = null;
                    }
                });
            d.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
            d.getWindow().getAttributes().privateFlags |=
                    WindowManager.LayoutParams.PRIVATE_FLAG_SHOW_FOR_ALL_USERS;
            d.show();
            mLowBatteryDialog = d;
        }
    }

    void playLowBatterySound() {
        final ContentResolver cr = mContext.getContentResolver();

        final int silenceAfter = Settings.Global.getInt(cr,
                Settings.Global.LOW_BATTERY_SOUND_TIMEOUT, 0);
        final long offTime = SystemClock.elapsedRealtime() - mScreenOffTime;
        if (silenceAfter > 0
                && mScreenOffTime > 0
                && offTime > silenceAfter) {
            Slog.i(TAG, "screen off too long (" + offTime + "ms, limit " + silenceAfter
                    + "ms): not waking up the user with low battery sound");
            return;
        }

        if (DEBUG) {
            Slog.d(TAG, "playing low battery sound. pick-a-doop!"); // WOMP-WOMP is deprecated
        }

        if (Settings.Global.getInt(cr, Settings.Global.POWER_SOUNDS_ENABLED, 1) == 1) {
            final String soundPath = Settings.Global.getString(cr,
                    Settings.Global.LOW_BATTERY_SOUND);
            if (soundPath != null) {
                final Uri soundUri = Uri.parse("file://" + soundPath);
                if (soundUri != null) {
                    final Ringtone sfx = RingtoneManager.getRingtone(mContext, soundUri);
                    if (sfx != null) {
                        sfx.setStreamType(AudioManager.STREAM_SYSTEM);
                        sfx.play();
                    }
                }
            }
        }
    }

    void dismissInvalidChargerDialog() {
        if (mInvalidChargerDialog != null) {
            mInvalidChargerDialog.dismiss();
        }
    }

    void showInvalidChargerDialog() {
        Slog.d(TAG, "showing invalid charger dialog");

        dismissLowBatteryWarning();

        AlertDialog.Builder b = new AlertDialog.Builder(mContext);
            b.setCancelable(true);
            b.setMessage(R.string.invalid_charger);
            b.setIconAttribute(android.R.attr.alertDialogIcon);
            b.setPositiveButton(android.R.string.ok, null);

        AlertDialog d = b.create();
            d.setOnDismissListener(new DialogInterface.OnDismissListener() {
                    public void onDismiss(DialogInterface dialog) {
                        mInvalidChargerDialog = null;
                        mBatteryLevelTextView = null;
                    }
                });

        d.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
        d.show();
        mInvalidChargerDialog = d;
    }

    public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
        pw.print("mLowBatteryAlertCloseLevel=");
        pw.println(mLowBatteryAlertCloseLevel);
        pw.print("mLowBatteryReminderLevels=");
        pw.println(Arrays.toString(mLowBatteryReminderLevels));
        pw.print("mInvalidChargerDialog=");
        pw.println(mInvalidChargerDialog == null ? "null" : mInvalidChargerDialog.toString());
        pw.print("mLowBatteryDialog=");
        pw.println(mLowBatteryDialog == null ? "null" : mLowBatteryDialog.toString());
        pw.print("mBatteryLevel=");
        pw.println(Integer.toString(mBatteryLevel));
        pw.print("mBatteryStatus=");
        pw.println(Integer.toString(mBatteryStatus));
        pw.print("mPlugType=");
        pw.println(Integer.toString(mPlugType));
        pw.print("mInvalidCharger=");
        pw.println(Integer.toString(mInvalidCharger));
        pw.print("mScreenOffTime=");
        pw.print(mScreenOffTime);
        if (mScreenOffTime >= 0) {
            pw.print(" (");
            pw.print(SystemClock.elapsedRealtime() - mScreenOffTime);
            pw.print(" ago)");
        }
        pw.println();
        pw.print("soundTimeout=");
        pw.println(Settings.Global.getInt(mContext.getContentResolver(),
                Settings.Global.LOW_BATTERY_SOUND_TIMEOUT, 0));
        pw.print("bucket: ");
        pw.println(Integer.toString(findBatteryLevelBucket(mBatteryLevel)));
    }
}
[java] view plain copy
/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.systemui.power;

import android.app.AlertDialog;
import android.content.BroadcastReceiver;
import android.content.ContentResolver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.media.AudioManager;
import android.media.Ringtone;
import android.media.RingtoneManager;
import android.net.Uri;
import android.os.BatteryManager;
import android.os.Handler;
import android.os.PowerManager;
import android.os.SystemClock;
import android.os.UserHandle;
import android.provider.Settings;
import android.util.Slog;
import android.view.View;
import android.view.WindowManager;
import android.widget.TextView;

import com.android.systemui.R;
import com.android.systemui.SystemUI;

import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.util.Arrays;

public class PowerUI extends SystemUI { //总体说一下，这里才是处理低电量提醒的地方，他接收的广播是Intent.ACTION_BATTERY_CHANGED
    static final String TAG = "PowerUI";

    static final boolean DEBUG = false;

    Handler mHandler = new Handler();

    int mBatteryLevel = 100;
    int mBatteryStatus = BatteryManager.BATTERY_STATUS_UNKNOWN;
    int mPlugType = 0;
    int mInvalidCharger = 0;

    int mLowBatteryAlertCloseLevel;
    int[] mLowBatteryReminderLevels = new int[2];

    AlertDialog mInvalidChargerDialog;
    AlertDialog mLowBatteryDialog;
    TextView mBatteryLevelTextView;

    private long mScreenOffTime = -1;

    public void start() {  //这个类会在手机启动后，在SystemUI 里启动(就是系统界面)。

        mLowBatteryAlertCloseLevel = mContext.getResources().getInteger( //电量告警取消值，值20
                com.android.internal.R.integer.config_lowBatteryCloseWarningLevel);
        mLowBatteryReminderLevels[0] = mContext.getResources().getInteger( //低电量提醒 15
                com.android.internal.R.integer.config_lowBatteryWarningLevel);
        mLowBatteryReminderLevels[1] = mContext.getResources().getInteger( //低电量临界值 4
                com.android.internal.R.integer.config_criticalBatteryWarningLevel);

        final PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
        mScreenOffTime = pm.isScreenOn() ? -1 : SystemClock.elapsedRealtime();

        // Register for Intent broadcasts for...
        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_BATTERY_CHANGED);
        filter.addAction(Intent.ACTION_SCREEN_OFF);
        filter.addAction(Intent.ACTION_SCREEN_ON);
        mContext.registerReceiver(mIntentReceiver, filter, null, mHandler);
    }

    /**
     * Buckets the battery level.
     *
     * The code in this function is a little weird because I couldn't comprehend
     * the bucket going up when the battery level was going down. --joeo
     *
     * 1 means that the battery is "ok"
     * 0 means that the battery is between "ok" and what we should warn about.
     * less than 0 means that the battery is low
     */
    private int findBatteryLevelBucket(int level) {   //这个方法是用来警告判断用的。
        if (level >= mLowBatteryAlertCloseLevel) {
            return 1;
        }
        if (level >= mLowBatteryReminderLevels[0]) {
            return 0;
        }
        final int N = mLowBatteryReminderLevels.length;
        for (int i=N-1; i>=0; i--) {
            if (level <= mLowBatteryReminderLevels[i]) {
                return -1-i;
            }
        }
        throw new RuntimeException("not possible!");
    }

    private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() { //重点，广播接收处理
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (action.equals(Intent.ACTION_BATTERY_CHANGED)) {  //电池电量改变
                final int oldBatteryLevel = mBatteryLevel; //下边就是根据Intent获取BatteryService传过来的电池属性
                mBatteryLevel = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 100); /
                final int oldBatteryStatus = mBatteryStatus;
                mBatteryStatus = intent.getIntExtra(BatteryManager.EXTRA_STATUS,
                        BatteryManager.BATTERY_STATUS_UNKNOWN);
                final int oldPlugType = mPlugType;
                mPlugType = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, 1);
                final int oldInvalidCharger = mInvalidCharger;
                mInvalidCharger = intent.getIntExtra(BatteryManager.EXTRA_INVALID_CHARGER, 0);

                final boolean plugged = mPlugType != 0;
                final boolean oldPlugged = oldPlugType != 0;

                int oldBucket = findBatteryLevelBucket(oldBatteryLevel); //这两个值特别有意思，就是说记录下老的电量，记录一下新的电量，比较电量是增加了，还是减小了
                int bucket = findBatteryLevelBucket(mBatteryLevel);

                if (DEBUG) {
                    Slog.d(TAG, "buckets   ....." + mLowBatteryAlertCloseLevel
                            + " .. " + mLowBatteryReminderLevels[0]
                            + " .. " + mLowBatteryReminderLevels[1]);
                    Slog.d(TAG, "level          " + oldBatteryLevel + " --> " + mBatteryLevel);
                    Slog.d(TAG, "status         " + oldBatteryStatus + " --> " + mBatteryStatus);
                    Slog.d(TAG, "plugType       " + oldPlugType + " --> " + mPlugType);
                    Slog.d(TAG, "invalidCharger " + oldInvalidCharger + " --> " + mInvalidCharger);
                    Slog.d(TAG, "bucket         " + oldBucket + " --> " + bucket);
                    Slog.d(TAG, "plugged        " + oldPlugged + " --> " + plugged);
                }

                if (oldInvalidCharger == 0 && mInvalidCharger != 0) {
                    Slog.d(TAG, "showing invalid charger warning");
                    showInvalidChargerDialog(); //就是充电器不识别的弹窗
                    return;
                } else if (oldInvalidCharger != 0 && mInvalidCharger == 0) {
                    dismissInvalidChargerDialog();
                } else if (mInvalidChargerDialog != null) {
                    // if invalid charger is showing, don't show low battery
                    return;
                }

                if (!plugged
                        && (bucket < oldBucket || oldPlugged)
                        && mBatteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN
                        && bucket < 0) {
                    showLowBatteryWarning(); //这里哈，低电量提醒的弹窗

                    // only play SFX when the dialog comes up or the bucket changes
                    if (bucket != oldBucket || oldPlugged) {
                        playLowBatterySound();
                    }
                } else if (plugged || (bucket > oldBucket && bucket > 0)) { //插上充电器或者充电电池电量超过20取消弹窗
                    dismissLowBatteryWarning();
                } else if (mBatteryLevelTextView != null) {
                    showLowBatteryWarning();
                }
            } else if (Intent.ACTION_SCREEN_OFF.equals(action)) {
                mScreenOffTime = SystemClock.elapsedRealtime();
            } else if (Intent.ACTION_SCREEN_ON.equals(action)) {
                mScreenOffTime = -1;
            } else {
                Slog.w(TAG, "unknown intent: " + intent);
            }
        }
    };

    void dismissLowBatteryWarning() {
        if (mLowBatteryDialog != null) {
            Slog.i(TAG, "closing low battery warning: level=" + mBatteryLevel);
            mLowBatteryDialog.dismiss();
        }
    }

    void showLowBatteryWarning() {
        Slog.i(TAG,
                ((mBatteryLevelTextView == null) ? "showing" : "updating")
                + " low battery warning: level=" + mBatteryLevel
                + " [" + findBatteryLevelBucket(mBatteryLevel) + "]");

        CharSequence levelText = mContext.getString(
                R.string.battery_low_percent_format, mBatteryLevel);

        if (mBatteryLevelTextView != null) {
            mBatteryLevelTextView.setText(levelText);
        } else {
            View v = View.inflate(mContext, R.layout.battery_low, null);
            mBatteryLevelTextView = (TextView)v.findViewById(R.id.level_percent);

            mBatteryLevelTextView.setText(levelText);

            AlertDialog.Builder b = new AlertDialog.Builder(mContext);
                b.setCancelable(true);
                b.setTitle(R.string.battery_low_title);
                b.setView(v);
                b.setIconAttribute(android.R.attr.alertDialogIcon);
                b.setPositiveButton(android.R.string.ok, null);

            final Intent intent = new Intent(Intent.ACTION_POWER_USAGE_SUMMARY);
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                    | Intent.FLAG_ACTIVITY_MULTIPLE_TASK
                    | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS
                    | Intent.FLAG_ACTIVITY_NO_HISTORY);
            if (intent.resolveActivity(mContext.getPackageManager()) != null) {
                b.setNegativeButton(R.string.battery_low_why,
                        new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        mContext.startActivityAsUser(intent, UserHandle.CURRENT);
                        dismissLowBatteryWarning();
                    }
                });
            }

            AlertDialog d = b.create();
            d.setOnDismissListener(new DialogInterface.OnDismissListener() {
                    @Override
                    public void onDismiss(DialogInterface dialog) {
                        mLowBatteryDialog = null;
                        mBatteryLevelTextView = null;
                    }
                });
            d.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
            d.getWindow().getAttributes().privateFlags |=
                    WindowManager.LayoutParams.PRIVATE_FLAG_SHOW_FOR_ALL_USERS;
            d.show();
            mLowBatteryDialog = d;
        }
    }

    void playLowBatterySound() {
        final ContentResolver cr = mContext.getContentResolver();

        final int silenceAfter = Settings.Global.getInt(cr,
                Settings.Global.LOW_BATTERY_SOUND_TIMEOUT, 0);
        final long offTime = SystemClock.elapsedRealtime() - mScreenOffTime;
        if (silenceAfter > 0
                && mScreenOffTime > 0
                && offTime > silenceAfter) {
            Slog.i(TAG, "screen off too long (" + offTime + "ms, limit " + silenceAfter
                    + "ms): not waking up the user with low battery sound");
            return;
        }

        if (DEBUG) {
            Slog.d(TAG, "playing low battery sound. pick-a-doop!"); // WOMP-WOMP is deprecated
        }

        if (Settings.Global.getInt(cr, Settings.Global.POWER_SOUNDS_ENABLED, 1) == 1) {
            final String soundPath = Settings.Global.getString(cr,
                    Settings.Global.LOW_BATTERY_SOUND);
            if (soundPath != null) {
                final Uri soundUri = Uri.parse("file://" + soundPath);
                if (soundUri != null) {
                    final Ringtone sfx = RingtoneManager.getRingtone(mContext, soundUri);
                    if (sfx != null) {
                        sfx.setStreamType(AudioManager.STREAM_SYSTEM);
                        sfx.play();
                    }
                }
            }
        }
    }

    void dismissInvalidChargerDialog() {
        if (mInvalidChargerDialog != null) {
            mInvalidChargerDialog.dismiss();
        }
    }

    void showInvalidChargerDialog() {
        Slog.d(TAG, "showing invalid charger dialog");

        dismissLowBatteryWarning();

        AlertDialog.Builder b = new AlertDialog.Builder(mContext);
            b.setCancelable(true);
            b.setMessage(R.string.invalid_charger);
            b.setIconAttribute(android.R.attr.alertDialogIcon);
            b.setPositiveButton(android.R.string.ok, null);

        AlertDialog d = b.create();
            d.setOnDismissListener(new DialogInterface.OnDismissListener() {
                    public void onDismiss(DialogInterface dialog) {
                        mInvalidChargerDialog = null;
                        mBatteryLevelTextView = null;
                    }
                });

        d.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
        d.show();
        mInvalidChargerDialog = d;
    }

    public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
        pw.print("mLowBatteryAlertCloseLevel=");
        pw.println(mLowBatteryAlertCloseLevel);
        pw.print("mLowBatteryReminderLevels=");
        pw.println(Arrays.toString(mLowBatteryReminderLevels));
        pw.print("mInvalidChargerDialog=");
        pw.println(mInvalidChargerDialog == null ? "null" : mInvalidChargerDialog.toString());
        pw.print("mLowBatteryDialog=");
        pw.println(mLowBatteryDialog == null ? "null" : mLowBatteryDialog.toString());
        pw.print("mBatteryLevel=");
        pw.println(Integer.toString(mBatteryLevel));
        pw.print("mBatteryStatus=");
        pw.println(Integer.toString(mBatteryStatus));
        pw.print("mPlugType=");
        pw.println(Integer.toString(mPlugType));
        pw.print("mInvalidCharger=");
        pw.println(Integer.toString(mInvalidCharger));
        pw.print("mScreenOffTime=");
        pw.print(mScreenOffTime);
        if (mScreenOffTime >= 0) {
            pw.print(" (");
            pw.print(SystemClock.elapsedRealtime() - mScreenOffTime);
            pw.print(" ago)");
        }
        pw.println();
        pw.print("soundTimeout=");
        pw.println(Settings.Global.getInt(mContext.getContentResolver(),
                Settings.Global.LOW_BATTERY_SOUND_TIMEOUT, 0));
        pw.print("bucket: ");
        pw.println(Integer.toString(findBatteryLevelBucket(mBatteryLevel)));
    }
}
总结一下：这个类就是接收电池电量改变的广播，然后弹窗提醒。

下一个类就是没电关机界面了，文件目录：\frameworks\base\services\java\com\android\server\ShutdownLowBatteryActivity.java
这个Activity的配置文件是这样的（\frameworks\base\core\res\AndroidManifest.xml）：
[html] view plaincopy
    android:theme="@android:style/Theme.Translucent.NoTitleBar"
    android:configChanges="orientation|keyboardHidden|screenSize"
    android:windowSoftInputMode="stateHidden"
    android:permission="android.permission.SHUTDOWN"
    android:excludeFromRecents="true">





[html] view plain copy
    android:theme="@android:style/Theme.Translucent.NoTitleBar"
    android:configChanges="orientation|keyboardHidden|screenSize"
    android:windowSoftInputMode="stateHidden"
    android:permission="android.permission.SHUTDOWN"
    android:excludeFromRecents="true">

android:theme="@android:style/Theme.Translucent.NoTitleBar"是API小于11的透明主题。这样弹出的dialog会是老版本的主题。（这个Activity是透明的）
对于Theme，因为是4.4，我更倾向于：android:theme="@android:style/Theme.Holo.Panel"

ShutdownLowBatteryActivity.java：
[java] view plaincopy
/*
* Copyright (C) 2009 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.server;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.KeyguardManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.os.Handler;
import android.util.Slog;
import android.view.Window;
import android.view.WindowManager;
import android.view.View;


//import com.android.internal.app.ShutdownThread;
import com.android.server.power.ShutdownThread;

import android.telephony.TelephonyManager;
import android.telephony.PhoneStateListener;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.content.ContentResolver;
import android.provider.Settings;

import java.io.IOException;

public class ShutdownLowBatteryActivity extends Activity {

    private static final String TAG = "ShutdownLowBatteryActivity";
    private boolean mConfirm;
    private int mSeconds = 15;//电池电量等于0 15秒内不插充电器就自动关机
    private AlertDialog mDialog;
    private Handler myHandler = new Handler();
    private Runnable myRunnable = new Runnable() { //这里数秒关机
        @Override
        public void run() {
            mSeconds --;
            if(mSeconds <1)
                mSeconds=0;
            mDialog.setMessage(getString(com.android.internal.R.string.low_battery_shutdown_after_seconds,mSeconds));

            if(mSeconds <= 1){
                myHandler.removeCallbacks(myRunnable);
                Handler h = new Handler();
                h.post(new Runnable() {
                    public void run() {
                        ShutdownThread.shutdown(ShutdownLowBatteryActivity.this, mConfirm);
                    }
                });
            }
            myHandler.postDelayed(myRunnable,1000);
        }
    };

    private BroadcastReceiver mReceiver;
    private MediaPlayer mplayer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mConfirm = getIntent().getBooleanExtra(Intent.EXTRA_KEY_CONFIRM, false);
        Slog.i(TAG, "onCreate(): confirm=" + mConfirm);

        //if(getIntent().getBooleanExtra("can_be_cancel", false)) { //这行注释掉了：然后当连上充电器后或者电量涨到20的时候，就取消倒计时关机
                mReceiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
                    if(Intent.ACTION_BATTERY_OKAY.equals(intent.getAction())|
                        Intent.ACTION_POWER_CONNECTED.equals(intent.getAction())){
                        ShutDownWakeLock.releaseCpuLock();
                        myHandler.removeCallbacks(myRunnable);
                        if(mReceiver != null)
                            unregisterReceiver(mReceiver);
                        finish();
                    }
                }
            };

         IntentFilter filter=new IntentFilter(Intent.ACTION_POWER_CONNECTED);
         filter.addAction(Intent.ACTION_BATTERY_OKAY);
         registerReceiver(mReceiver, filter);
         //}


        PhoneStateListener mPhoneStateListener = new PhoneStateListener() { //如果正数秒呢，电话呼入了。取消自动关机
            @Override
            public void onCallStateChanged(int state, String ignored) {
                if (state == TelephonyManager.CALL_STATE_RINGING) {
                    ShutDownWakeLock.releaseCpuLock();
                    myHandler.removeCallbacks(myRunnable);
                    finish();
                }
            }
        };

        TelephonyManager mTelephonyManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
        mTelephonyManager.listen(mPhoneStateListener,
                PhoneStateListener.LISTEN_CALL_STATE);
        requestWindowFeature(android.view.Window.FEATURE_NO_TITLE);
        Window win = getWindow();
        win.addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
                | WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD);
        win.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
                    | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON);

        setContentView(new View(this));
        mDialog=new AlertDialog.Builder(this).create();
        mDialog.setTitle(com.android.internal.R.string.low_battery_shutdown_title);
        mDialog.setMessage(getString(com.android.internal.R.string.low_battery_shutdown_after_seconds,mSeconds));
        if(!getIntent().getBooleanExtra("cant_be_cancel_by_button", false)) {//读取配置文件，是否运行取消，然后根据这个显示取消自动关机按钮
            mDialog.setButton(DialogInterface.BUTTON_NEUTRAL,getText(com.android.internal.R.string.cancel), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        myHandler.removeCallbacks(myRunnable);
                        dialog.cancel();
                        if(mReceiver != null)
                            unregisterReceiver(mReceiver);
                        finish();
                    }});
        }
        mDialog.setCancelable(false);
        //mDialog.getWindow().setType( WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
        mDialog.show();
        if(mConfirm == false){
            myHandler.postDelayed(myRunnable, 1000);
        }
        myHandler.post(new Runnable(){
            public void run(){
                final ContentResolver cr = getContentResolver();
                String path=Settings.System.getString(cr,Settings.System.NOTIFICATION_SOUND);

               mplayer=new MediaPlayer();
                try{
                    mplayer.reset();
                    mplayer.setDataSource("system/media/audio/ui/LowBattery.ogg");
                    mplayer.prepare();
                    mplayer.start();
                    mplayer.setOnCompletionListener(new OnCompletionListener() {
                        @Override
                        public void onCompletion(MediaPlayer mp) {
                            if(null != mplayer){
                                mplayer.stop();
                                mplayer.release();
                                mplayer = null;
                            }
                        }
                    });
                }
                catch(IOException e){

                }
            }
        });
    }
}
[java] view plain copy
/*
* Copyright (C) 2009 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.server;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.KeyguardManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.os.Handler;
import android.util.Slog;
import android.view.Window;
import android.view.WindowManager;
import android.view.View;


//import com.android.internal.app.ShutdownThread;
import com.android.server.power.ShutdownThread;

import android.telephony.TelephonyManager;
import android.telephony.PhoneStateListener;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.content.ContentResolver;
import android.provider.Settings;

import java.io.IOException;

public class ShutdownLowBatteryActivity extends Activity {

    private static final String TAG = "ShutdownLowBatteryActivity";
    private boolean mConfirm;
    private int mSeconds = 15;//电池电量等于0 15秒内不插充电器就自动关机
    private AlertDialog mDialog;
    private Handler myHandler = new Handler();
    private Runnable myRunnable = new Runnable() { //这里数秒关机
        @Override
        public void run() {
            mSeconds --;
            if(mSeconds <1)
                mSeconds=0;
            mDialog.setMessage(getString(com.android.internal.R.string.low_battery_shutdown_after_seconds,mSeconds));

            if(mSeconds <= 1){
                myHandler.removeCallbacks(myRunnable);
                Handler h = new Handler();
                h.post(new Runnable() {
                    public void run() {
                        ShutdownThread.shutdown(ShutdownLowBatteryActivity.this, mConfirm);
                    }
                });
            }
            myHandler.postDelayed(myRunnable,1000);
        }
    };

    private BroadcastReceiver mReceiver;
    private MediaPlayer mplayer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mConfirm = getIntent().getBooleanExtra(Intent.EXTRA_KEY_CONFIRM, false);
        Slog.i(TAG, "onCreate(): confirm=" + mConfirm);

        //if(getIntent().getBooleanExtra("can_be_cancel", false)) { //这行注释掉了：然后当连上充电器后或者电量涨到20的时候，就取消倒计时关机
                mReceiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
                    if(Intent.ACTION_BATTERY_OKAY.equals(intent.getAction())|
                        Intent.ACTION_POWER_CONNECTED.equals(intent.getAction())){
                        ShutDownWakeLock.releaseCpuLock();
                        myHandler.removeCallbacks(myRunnable);
                        if(mReceiver != null)
                            unregisterReceiver(mReceiver);
                        finish();
                    }
                }
            };

         IntentFilter filter=new IntentFilter(Intent.ACTION_POWER_CONNECTED);
         filter.addAction(Intent.ACTION_BATTERY_OKAY);
         registerReceiver(mReceiver, filter);
         //}


        PhoneStateListener mPhoneStateListener = new PhoneStateListener() { //如果正数秒呢，电话呼入了。取消自动关机
            @Override
            public void onCallStateChanged(int state, String ignored) {
                if (state == TelephonyManager.CALL_STATE_RINGING) {
                    ShutDownWakeLock.releaseCpuLock();
                    myHandler.removeCallbacks(myRunnable);
                    finish();
                }
            }
        };

        TelephonyManager mTelephonyManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
        mTelephonyManager.listen(mPhoneStateListener,
                PhoneStateListener.LISTEN_CALL_STATE);
        requestWindowFeature(android.view.Window.FEATURE_NO_TITLE);
        Window win = getWindow();
        win.addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
                | WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD);
        win.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
                    | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON);

        setContentView(new View(this));
        mDialog=new AlertDialog.Builder(this).create();
        mDialog.setTitle(com.android.internal.R.string.low_battery_shutdown_title);
        mDialog.setMessage(getString(com.android.internal.R.string.low_battery_shutdown_after_seconds,mSeconds));
        if(!getIntent().getBooleanExtra("cant_be_cancel_by_button", false)) {//读取配置文件，是否运行取消，然后根据这个显示取消自动关机按钮
            mDialog.setButton(DialogInterface.BUTTON_NEUTRAL,getText(com.android.internal.R.string.cancel), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        myHandler.removeCallbacks(myRunnable);
                        dialog.cancel();
                        if(mReceiver != null)
                            unregisterReceiver(mReceiver);
                        finish();
                    }});
        }
        mDialog.setCancelable(false);
        //mDialog.getWindow().setType( WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
        mDialog.show();
        if(mConfirm == false){
            myHandler.postDelayed(myRunnable, 1000);
        }
        myHandler.post(new Runnable(){
            public void run(){
                final ContentResolver cr = getContentResolver();
                String path=Settings.System.getString(cr,Settings.System.NOTIFICATION_SOUND);

               mplayer=new MediaPlayer();
                try{
                    mplayer.reset();
                    mplayer.setDataSource("system/media/audio/ui/LowBattery.ogg");
                    mplayer.prepare();
                    mplayer.start();
                    mplayer.setOnCompletionListener(new OnCompletionListener() {
                        @Override
                        public void onCompletion(MediaPlayer mp) {
                            if(null != mplayer){
                                mplayer.stop();
                                mplayer.release();
                                mplayer = null;
                            }
                        }
                    });
                }
                catch(IOException e){

                }
            }
        });
    }
}
总结如下：这个类就是弹窗计时，提醒不连充电器就要关机了。

最后一个相关的类，文件路径：\frameworks\base\packages\SystemUI\src\com\android\systemui\BatteryMeterView.java
这个类是自定义控件，定义在手机状态栏里：

[java] view plaincopy
/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.systemui;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.graphics.RectF;
import android.graphics.Typeface;
import android.os.BatteryManager;
import android.os.Bundle;
import android.provider.Settings;
import android.util.AttributeSet;
import android.view.View;

public class BatteryMeterView extends View implements DemoMode {
    public static final String TAG = BatteryMeterView.class.getSimpleName();
    public static final String ACTION_LEVEL_TEST = "com.android.systemui.BATTERY_LEVEL_TEST";

    public static final boolean ENABLE_PERCENT = true;
    public static final boolean SINGLE_DIGIT_PERCENT = false;
    public static final boolean SHOW_100_PERCENT = false;

    public static final int FULL = 96;
    public static final int EMPTY = 4;

    public static final float SUBPIXEL = 0.4f;  // inset rects for softer edges

    int[] mColors;

    boolean mShowPercent = true;
    Paint mFramePaint, mBatteryPaint, mWarningTextPaint, mTextPaint, mBoltPaint;
    int mButtonHeight;
    private float mTextHeight, mWarningTextHeight;

    private int mHeight;
    private int mWidth;
    private String mWarningString;
    private final int mChargeColor;
    private final float[] mBoltPoints;
    private final Path mBoltPath = new Path();

    private final RectF mFrame = new RectF();
    private final RectF mButtonFrame = new RectF();
    private final RectF mClipFrame = new RectF();
    private final RectF mBoltFrame = new RectF();

    private class BatteryTracker extends BroadcastReceiver {
        public static final int UNKNOWN_LEVEL = -1;

        // current battery status
        int level = UNKNOWN_LEVEL;
        String percentStr;
        int plugType;
        boolean plugged;
        int health;
        int status;
        String technology;
        int voltage;
        int temperature;
        boolean testmode = false;

        @Override
        public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
            if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { //接收电量改变的广播，取电池状态的属性
                if (testmode && ! intent.getBooleanExtra("testmode", false)) return;

                level = (int)(100f
                        * intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0)
                        / intent.getIntExtra(BatteryManager.EXTRA_SCALE, 100));

                plugType = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, 0);
                plugged = plugType != 0;
                health = intent.getIntExtra(BatteryManager.EXTRA_HEALTH,
                        BatteryManager.BATTERY_HEALTH_UNKNOWN);
                status = intent.getIntExtra(BatteryManager.EXTRA_STATUS,
                        BatteryManager.BATTERY_STATUS_UNKNOWN);
                technology = intent.getStringExtra(BatteryManager.EXTRA_TECHNOLOGY);
                voltage = intent.getIntExtra(BatteryManager.EXTRA_VOLTAGE, 0);
                temperature = intent.getIntExtra(BatteryManager.EXTRA_TEMPERATURE, 0);

                setContentDescription(
                        context.getString(R.string.accessibility_battery_level, level));
                postInvalidate();
            } else if (action.equals(ACTION_LEVEL_TEST)) {
                testmode = true;
                post(new Runnable() {
                    int curLevel = 0;
                    int incr = 1;
                    int saveLevel = level;
                    int savePlugged = plugType;
                    Intent dummy = new Intent(Intent.ACTION_BATTERY_CHANGED);
                    @Override
                    public void run() {
                        if (curLevel < 0) {
                            testmode = false;
                            dummy.putExtra("level", saveLevel);
                            dummy.putExtra("plugged", savePlugged);
                            dummy.putExtra("testmode", false);
                        } else {
                            dummy.putExtra("level", curLevel);
                            dummy.putExtra("plugged", incr > 0 ? BatteryManager.BATTERY_PLUGGED_AC : 0);
                            dummy.putExtra("testmode", true);
                        }
                        getContext().sendBroadcast(dummy);

                        if (!testmode) return;

                        curLevel += incr;
                        if (curLevel == 100) {
                            incr *= -1;
                        }
                        postDelayed(this, 200);
                    }
                });
            }
        }
    }

    BatteryTracker mTracker = new BatteryTracker();

    @Override
    public void onAttachedToWindow() {
        super.onAttachedToWindow();

        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_BATTERY_CHANGED);
        filter.addAction(ACTION_LEVEL_TEST);
        final Intent sticky = getContext().registerReceiver(mTracker, filter);
        if (sticky != null) {
            // preload the battery level
            mTracker.onReceive(getContext(), sticky);
        }
    }

    @Override
    public void onDetachedFromWindow() {
        super.onDetachedFromWindow();

        getContext().unregisterReceiver(mTracker);
    }

    public BatteryMeterView(Context context) {
        this(context, null, 0);
    }

    public BatteryMeterView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public BatteryMeterView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        final Resources res = context.getResources();
        TypedArray levels = res.obtainTypedArray(R.array.batterymeter_color_levels);
        TypedArray colors = res.obtainTypedArray(R.array.batterymeter_color_values);

        final int N = levels.length();
        mColors = new int[2*N];
        for (int i=0; i             mColors[2*i] = levels.getInt(i, 0);
            mColors[2*i+1] = colors.getColor(i, 0);
        }
        levels.recycle();
        colors.recycle();
        mShowPercent = ENABLE_PERCENT && 0 != Settings.System.getInt(
                context.getContentResolver(), "status_bar_show_battery_percent", 0);

        mWarningString = context.getString(R.string.battery_meter_very_low_overlay_symbol);

        mFramePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mFramePaint.setColor(res.getColor(R.color.batterymeter_frame_color));
        mFramePaint.setDither(true);
        mFramePaint.setStrokeWidth(0);
        mFramePaint.setStyle(Paint.Style.FILL_AND_STROKE);
        mFramePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP));

        mBatteryPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mBatteryPaint.setDither(true);
        mBatteryPaint.setStrokeWidth(0);
        mBatteryPaint.setStyle(Paint.Style.FILL_AND_STROKE);

        mTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mTextPaint.setColor(0xFFFFFFFF);
        Typeface font = Typeface.create("sans-serif-condensed", Typeface.NORMAL);
        mTextPaint.setTypeface(font);
        mTextPaint.setTextAlign(Paint.Align.CENTER);

        mWarningTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mWarningTextPaint.setColor(mColors[1]);
        font = Typeface.create("sans-serif", Typeface.BOLD);
        mWarningTextPaint.setTypeface(font);
        mWarningTextPaint.setTextAlign(Paint.Align.CENTER);

        mChargeColor = getResources().getColor(R.color.batterymeter_charge_color);

        mBoltPaint = new Paint();
        mBoltPaint.setAntiAlias(true);
        mBoltPaint.setColor(res.getColor(R.color.batterymeter_bolt_color));
        mBoltPoints = loadBoltPoints(res);
        setLayerType(View.LAYER_TYPE_SOFTWARE, null);
    }

    private static float[] loadBoltPoints(Resources res) {
        final int[] pts = res.getIntArray(R.array.batterymeter_bolt_points);
        int maxX = 0, maxY = 0;
        for (int i = 0; i < pts.length; i += 2) {
            maxX = Math.max(maxX, pts[i]);
            maxY = Math.max(maxY, pts[i + 1]);
        }
        final float[] ptsF = new float[pts.length];
        for (int i = 0; i < pts.length; i += 2) {
            ptsF[i] = (float)pts[i] / maxX;
            ptsF[i + 1] = (float)pts[i + 1] / maxY;
        }
        return ptsF;
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mHeight = h;
        mWidth = w;
        mWarningTextPaint.setTextSize(h * 0.75f);
        mWarningTextHeight = -mWarningTextPaint.getFontMetrics().ascent;
    }

    private int getColorForLevel(int percent) {
        int thresh, color = 0;
        for (int i=0; i             thresh = mColors[i];
            color = mColors[i+1];
            if (percent <= thresh) return color;
        }
        return color;
    }

    @Override
    public void draw(Canvas c) {  //通过电池属性绘制图标
        BatteryTracker tracker = mDemoMode ? mDemoTracker : mTracker;
        final int level = tracker.level;

        if (level == BatteryTracker.UNKNOWN_LEVEL) return;

        float drawFrac = (float) level / 100f;
        final int pt = getPaddingTop();
        final int pl = getPaddingLeft();
        final int pr = getPaddingRight();
        final int pb = getPaddingBottom();
        int height = mHeight - pt - pb;
        int width = mWidth - pl - pr;

        mButtonHeight = (int) (height * 0.12f);

        mFrame.set(0, 0, width, height);
        mFrame.offset(pl, pt);

        mButtonFrame.set(  //这个就是电池图标上边的突起
                mFrame.left + width * 0.25f,
                mFrame.top,
                mFrame.right - width * 0.25f,
                mFrame.top + mButtonHeight + 5 /*cover frame border of intersecting area*/);

        mButtonFrame.top += SUBPIXEL;
        mButtonFrame.left += SUBPIXEL;
        mButtonFrame.right -= SUBPIXEL;

        mFrame.top += mButtonHeight; //电池图标桶装图
        mFrame.left += SUBPIXEL;
        mFrame.top += SUBPIXEL;
        mFrame.right -= SUBPIXEL;
        mFrame.bottom -= SUBPIXEL;

        // first, draw the battery shape
        c.drawRect(mFrame, mFramePaint);

        // fill 'er up
        final int color = tracker.plugged ? mChargeColor : getColorForLevel(level); //根据等级获取颜色，如果是15以下，就是红色。15以上是白色
        mBatteryPaint.setColor(color);

        if (level >= FULL) { //96时，电池图标里面填充完整，满电。
            drawFrac = 1f;
        } else if (level <= EMPTY) { //这个变量是说，当电量小于4的时候，电池图标里面没有填充色，空电量
            drawFrac = 0f;
        }

        c.drawRect(mButtonFrame, drawFrac == 1f ? mBatteryPaint : mFramePaint);

        mClipFrame.set(mFrame);
        mClipFrame.top += (mFrame.height() * (1f - drawFrac));

        c.save(Canvas.CLIP_SAVE_FLAG);
        c.clipRect(mClipFrame);//在mFrame区域中保持mClipFrame的区域不变，参考下句注释
        c.drawRect(mFrame, mBatteryPaint);//在mFrame中，把除去mClipFrame的区域绘制。（电量状态，如果是15以下，就是红色。15以上是白色）
        c.restore();

        if (tracker.plugged) { //这里就犀利了。这是说插上充电器就画一个闪电
            // draw the bolt
            final float bl = mFrame.left + mFrame.width() / 4.5f;
            final float bt = mFrame.top + mFrame.height() / 6f;
            final float br = mFrame.right - mFrame.width() / 7f;
            final float bb = mFrame.bottom - mFrame.height() / 10f;
            if (mBoltFrame.left != bl || mBoltFrame.top != bt
                    || mBoltFrame.right != br || mBoltFrame.bottom != bb) {
                mBoltFrame.set(bl, bt, br, bb);
                mBoltPath.reset();
                mBoltPath.moveTo(
                        mBoltFrame.left + mBoltPoints[0] * mBoltFrame.width(),
                        mBoltFrame.top + mBoltPoints[1] * mBoltFrame.height());
                for (int i = 2; i < mBoltPoints.length; i += 2) {
                    mBoltPath.lineTo(
                            mBoltFrame.left + mBoltPoints[i] * mBoltFrame.width(),
                            mBoltFrame.top + mBoltPoints[i + 1] * mBoltFrame.height());
                }
                mBoltPath.lineTo(
                        mBoltFrame.left + mBoltPoints[0] * mBoltFrame.width(),
                        mBoltFrame.top + mBoltPoints[1] * mBoltFrame.height());
            }
            c.drawPath(mBoltPath, mBoltPaint);
        } else if (level <= EMPTY) { //这个是空电量的时候，画一个红色的感叹号
            final float x = mWidth * 0.5f;
            final float y = (mHeight + mWarningTextHeight) * 0.48f;
            c.drawText(mWarningString, x, y, mWarningTextPaint);
        } else if (mShowPercent && !(tracker.level == 100 && !SHOW_100_PERCENT)) { //以文字显示电量。不过这个没有用到（除非mShowPercent变量获取的配置属性为true）
            mTextPaint.setTextSize(height *
                    (SINGLE_DIGIT_PERCENT ? 0.75f
                            : (tracker.level == 100 ? 0.38f : 0.5f)));
            mTextHeight = -mTextPaint.getFontMetrics().ascent;

            final String str = String.valueOf(SINGLE_DIGIT_PERCENT ? (level/10) : level);
            final float x = mWidth * 0.5f;
            final float y = (mHeight + mTextHeight) * 0.47f;
            c.drawText(str,
                    x,
                    y,
                    mTextPaint);
        }
    }

    private boolean mDemoMode;
    private BatteryTracker mDemoTracker = new BatteryTracker();

    @Override
    public void dispatchDemoCommand(String command, Bundle args) {
        if (!mDemoMode && command.equals(COMMAND_ENTER)) {
            mDemoMode = true;
            mDemoTracker.level = mTracker.level;
            mDemoTracker.plugged = mTracker.plugged;
        } else if (mDemoMode && command.equals(COMMAND_EXIT)) {
            mDemoMode = false;
            postInvalidate();
        } else if (mDemoMode && command.equals(COMMAND_BATTERY)) {
           String level = args.getString("level");
           String plugged = args.getString("plugged");
           if (level != null) {
               mDemoTracker.level = Math.min(Math.max(Integer.parseInt(level), 0), 100);
           }
           if (plugged != null) {
               mDemoTracker.plugged = Boolean.parseBoolean(plugged);
           }
           postInvalidate();
        }
    }
}
[java] view plain copy
/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.android.systemui;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.graphics.RectF;
import android.graphics.Typeface;
import android.os.BatteryManager;
import android.os.Bundle;
import android.provider.Settings;
import android.util.AttributeSet;
import android.view.View;

public class BatteryMeterView extends View implements DemoMode {
    public static final String TAG = BatteryMeterView.class.getSimpleName();
    public static final String ACTION_LEVEL_TEST = "com.android.systemui.BATTERY_LEVEL_TEST";

    public static final boolean ENABLE_PERCENT = true;
    public static final boolean SINGLE_DIGIT_PERCENT = false;
    public static final boolean SHOW_100_PERCENT = false;

    public static final int FULL = 96;
    public static final int EMPTY = 4;

    public static final float SUBPIXEL = 0.4f;  // inset rects for softer edges

    int[] mColors;

    boolean mShowPercent = true;
    Paint mFramePaint, mBatteryPaint, mWarningTextPaint, mTextPaint, mBoltPaint;
    int mButtonHeight;
    private float mTextHeight, mWarningTextHeight;

    private int mHeight;
    private int mWidth;
    private String mWarningString;
    private final int mChargeColor;
    private final float[] mBoltPoints;
    private final Path mBoltPath = new Path();

    private final RectF mFrame = new RectF();
    private final RectF mButtonFrame = new RectF();
    private final RectF mClipFrame = new RectF();
    private final RectF mBoltFrame = new RectF();

    private class BatteryTracker extends BroadcastReceiver {
        public static final int UNKNOWN_LEVEL = -1;

        // current battery status
        int level = UNKNOWN_LEVEL;
        String percentStr;
        int plugType;
        boolean plugged;
        int health;
        int status;
        String technology;
        int voltage;
        int temperature;
        boolean testmode = false;

        @Override
        public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
            if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { //接收电量改变的广播，取电池状态的属性
                if (testmode && ! intent.getBooleanExtra("testmode", false)) return;

                level = (int)(100f
                        * intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0)
                        / intent.getIntExtra(BatteryManager.EXTRA_SCALE, 100));

                plugType = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, 0);
                plugged = plugType != 0;
                health = intent.getIntExtra(BatteryManager.EXTRA_HEALTH,
                        BatteryManager.BATTERY_HEALTH_UNKNOWN);
                status = intent.getIntExtra(BatteryManager.EXTRA_STATUS,
                        BatteryManager.BATTERY_STATUS_UNKNOWN);
                technology = intent.getStringExtra(BatteryManager.EXTRA_TECHNOLOGY);
                voltage = intent.getIntExtra(BatteryManager.EXTRA_VOLTAGE, 0);
                temperature = intent.getIntExtra(BatteryManager.EXTRA_TEMPERATURE, 0);

                setContentDescription(
                        context.getString(R.string.accessibility_battery_level, level));
                postInvalidate();
            } else if (action.equals(ACTION_LEVEL_TEST)) {
                testmode = true;
                post(new Runnable() {
                    int curLevel = 0;
                    int incr = 1;
                    int saveLevel = level;
                    int savePlugged = plugType;
                    Intent dummy = new Intent(Intent.ACTION_BATTERY_CHANGED);
                    @Override
                    public void run() {
                        if (curLevel < 0) {
                            testmode = false;
                            dummy.putExtra("level", saveLevel);
                            dummy.putExtra("plugged", savePlugged);
                            dummy.putExtra("testmode", false);
                        } else {
                            dummy.putExtra("level", curLevel);
                            dummy.putExtra("plugged", incr > 0 ? BatteryManager.BATTERY_PLUGGED_AC : 0);
                            dummy.putExtra("testmode", true);
                        }
                        getContext().sendBroadcast(dummy);

                        if (!testmode) return;

                        curLevel += incr;
                        if (curLevel == 100) {
                            incr *= -1;
                        }
                        postDelayed(this, 200);
                    }
                });
            }
        }
    }

    BatteryTracker mTracker = new BatteryTracker();

    @Override
    public void onAttachedToWindow() {
        super.onAttachedToWindow();

        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_BATTERY_CHANGED);
        filter.addAction(ACTION_LEVEL_TEST);
        final Intent sticky = getContext().registerReceiver(mTracker, filter);
        if (sticky != null) {
            // preload the battery level
            mTracker.onReceive(getContext(), sticky);
        }
    }

    @Override
    public void onDetachedFromWindow() {
        super.onDetachedFromWindow();

        getContext().unregisterReceiver(mTracker);
    }

    public BatteryMeterView(Context context) {
        this(context, null, 0);
    }

    public BatteryMeterView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public BatteryMeterView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        final Resources res = context.getResources();
        TypedArray levels = res.obtainTypedArray(R.array.batterymeter_color_levels);
        TypedArray colors = res.obtainTypedArray(R.array.batterymeter_color_values);

        final int N = levels.length();
        mColors = new int[2*N];
        for (int i=0; i             mColors[2*i] = levels.getInt(i, 0);
            mColors[2*i+1] = colors.getColor(i, 0);
        }
        levels.recycle();
        colors.recycle();
        mShowPercent = ENABLE_PERCENT && 0 != Settings.System.getInt(
                context.getContentResolver(), "status_bar_show_battery_percent", 0);

        mWarningString = context.getString(R.string.battery_meter_very_low_overlay_symbol);

        mFramePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mFramePaint.setColor(res.getColor(R.color.batterymeter_frame_color));
        mFramePaint.setDither(true);
        mFramePaint.setStrokeWidth(0);
        mFramePaint.setStyle(Paint.Style.FILL_AND_STROKE);
        mFramePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP));

        mBatteryPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mBatteryPaint.setDither(true);
        mBatteryPaint.setStrokeWidth(0);
        mBatteryPaint.setStyle(Paint.Style.FILL_AND_STROKE);

        mTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mTextPaint.setColor(0xFFFFFFFF);
        Typeface font = Typeface.create("sans-serif-condensed", Typeface.NORMAL);
        mTextPaint.setTypeface(font);
        mTextPaint.setTextAlign(Paint.Align.CENTER);

        mWarningTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mWarningTextPaint.setColor(mColors[1]);
        font = Typeface.create("sans-serif", Typeface.BOLD);
        mWarningTextPaint.setTypeface(font);
        mWarningTextPaint.setTextAlign(Paint.Align.CENTER);

        mChargeColor = getResources().getColor(R.color.batterymeter_charge_color);

        mBoltPaint = new Paint();
        mBoltPaint.setAntiAlias(true);
        mBoltPaint.setColor(res.getColor(R.color.batterymeter_bolt_color));
        mBoltPoints = loadBoltPoints(res);
        setLayerType(View.LAYER_TYPE_SOFTWARE, null);
    }

    private static float[] loadBoltPoints(Resources res) {
        final int[] pts = res.getIntArray(R.array.batterymeter_bolt_points);
        int maxX = 0, maxY = 0;
        for (int i = 0; i < pts.length; i += 2) {
            maxX = Math.max(maxX, pts[i]);
            maxY = Math.max(maxY, pts[i + 1]);
        }
        final float[] ptsF = new float[pts.length];
        for (int i = 0; i < pts.length; i += 2) {
            ptsF[i] = (float)pts[i] / maxX;
            ptsF[i + 1] = (float)pts[i + 1] / maxY;
        }
        return ptsF;
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mHeight = h;
        mWidth = w;
        mWarningTextPaint.setTextSize(h * 0.75f);
        mWarningTextHeight = -mWarningTextPaint.getFontMetrics().ascent;
    }

    private int getColorForLevel(int percent) {
        int thresh, color = 0;
        for (int i=0; i             thresh = mColors[i];
            color = mColors[i+1];
            if (percent <= thresh) return color;
        }
        return color;
    }

    @Override
    public void draw(Canvas c) {  //通过电池属性绘制图标
        BatteryTracker tracker = mDemoMode ? mDemoTracker : mTracker;
        final int level = tracker.level;

        if (level == BatteryTracker.UNKNOWN_LEVEL) return;

        float drawFrac = (float) level / 100f;
        final int pt = getPaddingTop();
        final int pl = getPaddingLeft();
        final int pr = getPaddingRight();
        final int pb = getPaddingBottom();
        int height = mHeight - pt - pb;
        int width = mWidth - pl - pr;

        mButtonHeight = (int) (height * 0.12f);

        mFrame.set(0, 0, width, height);
        mFrame.offset(pl, pt);

        mButtonFrame.set(  //这个就是电池图标上边的突起
                mFrame.left + width * 0.25f,
                mFrame.top,
                mFrame.right - width * 0.25f,
                mFrame.top + mButtonHeight + 5 /*cover frame border of intersecting area*/);

        mButtonFrame.top += SUBPIXEL;
        mButtonFrame.left += SUBPIXEL;
        mButtonFrame.right -= SUBPIXEL;

        mFrame.top += mButtonHeight; //电池图标桶装图
        mFrame.left += SUBPIXEL;
        mFrame.top += SUBPIXEL;
        mFrame.right -= SUBPIXEL;
        mFrame.bottom -= SUBPIXEL;

        // first, draw the battery shape
        c.drawRect(mFrame, mFramePaint);

        // fill 'er up
        final int color = tracker.plugged ? mChargeColor : getColorForLevel(level); //根据等级获取颜色，如果是15以下，就是红色。15以上是白色
        mBatteryPaint.setColor(color);

        if (level >= FULL) { //96时，电池图标里面填充完整，满电。
            drawFrac = 1f;
        } else if (level <= EMPTY) { //这个变量是说，当电量小于4的时候，电池图标里面没有填充色，空电量
            drawFrac = 0f;
        }

        c.drawRect(mButtonFrame, drawFrac == 1f ? mBatteryPaint : mFramePaint);

        mClipFrame.set(mFrame);
        mClipFrame.top += (mFrame.height() * (1f - drawFrac));

        c.save(Canvas.CLIP_SAVE_FLAG);
        c.clipRect(mClipFrame);//在mFrame区域中保持mClipFrame的区域不变，参考下句注释
        c.drawRect(mFrame, mBatteryPaint);//在mFrame中，把除去mClipFrame的区域绘制。（电量状态，如果是15以下，就是红色。15以上是白色）
        c.restore();

        if (tracker.plugged) { //这里就犀利了。这是说插上充电器就画一个闪电
            // draw the bolt
            final float bl = mFrame.left + mFrame.width() / 4.5f;
            final float bt = mFrame.top + mFrame.height() / 6f;
            final float br = mFrame.right - mFrame.width() / 7f;
            final float bb = mFrame.bottom - mFrame.height() / 10f;
            if (mBoltFrame.left != bl || mBoltFrame.top != bt
                    || mBoltFrame.right != br || mBoltFrame.bottom != bb) {
                mBoltFrame.set(bl, bt, br, bb);
                mBoltPath.reset();
                mBoltPath.moveTo(
                        mBoltFrame.left + mBoltPoints[0] * mBoltFrame.width(),
                        mBoltFrame.top + mBoltPoints[1] * mBoltFrame.height());
                for (int i = 2; i < mBoltPoints.length; i += 2) {
                    mBoltPath.lineTo(
                            mBoltFrame.left + mBoltPoints[i] * mBoltFrame.width(),
                            mBoltFrame.top + mBoltPoints[i + 1] * mBoltFrame.height());
                }
                mBoltPath.lineTo(
                        mBoltFrame.left + mBoltPoints[0] * mBoltFrame.width(),
                        mBoltFrame.top + mBoltPoints[1] * mBoltFrame.height());
            }
            c.drawPath(mBoltPath, mBoltPaint);
        } else if (level <= EMPTY) { //这个是空电量的时候，画一个红色的感叹号
            final float x = mWidth * 0.5f;
            final float y = (mHeight + mWarningTextHeight) * 0.48f;
            c.drawText(mWarningString, x, y, mWarningTextPaint);
        } else if (mShowPercent && !(tracker.level == 100 && !SHOW_100_PERCENT)) { //以文字显示电量。不过这个没有用到（除非mShowPercent变量获取的配置属性为true）
            mTextPaint.setTextSize(height *
                    (SINGLE_DIGIT_PERCENT ? 0.75f
                            : (tracker.level == 100 ? 0.38f : 0.5f)));
            mTextHeight = -mTextPaint.getFontMetrics().ascent;

            final String str = String.valueOf(SINGLE_DIGIT_PERCENT ? (level/10) : level);
            final float x = mWidth * 0.5f;
            final float y = (mHeight + mTextHeight) * 0.47f;
            c.drawText(str,
                    x,
                    y,
                    mTextPaint);
        }
    }

    private boolean mDemoMode;
    private BatteryTracker mDemoTracker = new BatteryTracker();

    @Override
    public void dispatchDemoCommand(String command, Bundle args) {
        if (!mDemoMode && command.equals(COMMAND_ENTER)) {
            mDemoMode = true;
            mDemoTracker.level = mTracker.level;
            mDemoTracker.plugged = mTracker.plugged;
        } else if (mDemoMode && command.equals(COMMAND_EXIT)) {
            mDemoMode = false;
            postInvalidate();
        } else if (mDemoMode && command.equals(COMMAND_BATTERY)) {
           String level = args.getString("level");
           String plugged = args.getString("plugged");
           if (level != null) {
               mDemoTracker.level = Math.min(Math.max(Integer.parseInt(level), 0), 100);
           }
           if (plugged != null) {
               mDemoTracker.plugged = Boolean.parseBoolean(plugged);
           }
           postInvalidate();
        }
    }
}

总结：这个类就是绘制状态栏里面电量图标的自定义控件。

android 4.4 batteryservice 电池电量显示分析

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