Android电量信息

1.电池电量管理

    Android的电量在Framework层都是以广播消息的形式发布的，发布者是BatteryService.java. BatteryService的原理就是利用UEventObserver的一个实例监测kernel层电量改变的事件。电量的驱动文件都放在/sys/class/power_supply目录下面，里面包括电压，电量百分比，AC/USB状态等信息。当电量改变时候JNI文件com_android_server_BatteryService.cpp会将/sys/class/power_supply里面的所有信息更新至BatteryService.java中

static void android_server_BatteryService_update(JNIEnv* env, jobject obj)
{
    setBooleanField(env, obj, gPaths.acOnlinePath, gFieldIds.mAcOnline);
    setBooleanField(env, obj, gPaths.usbOnlinePath, gFieldIds.mUsbOnline);
    setBooleanField(env, obj, gPaths.batteryPresentPath, gFieldIds.mBatteryPresent);
    
    setIntField(env, obj, gPaths.batteryCapacityPath, gFieldIds.mBatteryLevel);
    setVoltageField(env, obj, gPaths.batteryVoltagePath, gFieldIds.mBatteryVoltage);
    setIntField(env, obj, gPaths.batteryTemperaturePath, gFieldIds.mBatteryTemperature);
    
    const int SIZE = 128;
    char buf[SIZE];
    
    if (readFromFile(gPaths.batteryStatusPath, buf, SIZE) > 0)
        env->SetIntField(obj, gFieldIds.mBatteryStatus, getBatteryStatus(buf));
    else
        env->SetIntField(obj, gFieldIds.mBatteryStatus,
                         gConstants.statusUnknown);
    
    if (readFromFile(gPaths.batteryHealthPath, buf, SIZE) > 0)
        env->SetIntField(obj, gFieldIds.mBatteryHealth, getBatteryHealth(buf));

    if (readFromFile(gPaths.batteryTechnologyPath, buf, SIZE) > 0)
        env->SetObjectField(obj, gFieldIds.mBatteryTechnology, env->NewStringUTF(buf));
}

BatteryService再将电量信息以广播形式发布出去

    private final void sendIntent() {
        //  Pack up the values and broadcast them to everyone
        Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
                | Intent.FLAG_RECEIVER_REPLACE_PENDING);

        int icon = getIcon(mBatteryLevel);

        intent.putExtra(BatteryManager.EXTRA_STATUS, mBatteryStatus);
        intent.putExtra(BatteryManager.EXTRA_HEALTH, mBatteryHealth);
        intent.putExtra(BatteryManager.EXTRA_PRESENT, mBatteryPresent);
        intent.putExtra(BatteryManager.EXTRA_LEVEL, mBatteryLevel);
        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, mBatteryVoltage);
        intent.putExtra(BatteryManager.EXTRA_TEMPERATURE, mBatteryTemperature);
        intent.putExtra(BatteryManager.EXTRA_TECHNOLOGY, mBatteryTechnology);
        intent.putExtra(BatteryManager.EXTRA_INVALID_CHARGER, mInvalidCharger);

        if (false) {
            Slog.d(TAG, "level:" + mBatteryLevel +
                    " scale:" + BATTERY_SCALE + " status:" + mBatteryStatus +
                    " health:" + mBatteryHealth +  " present:" + mBatteryPresent +
                    " voltage: " + mBatteryVoltage +
                    " temperature: " + mBatteryTemperature +
                    " technology: " + mBatteryTechnology +
                    " AC powered:" + mAcOnline + " USB powered:" + mUsbOnline +
                    " icon:" + icon  + " invalid charger:" + mInvalidCharger);
        }

        ActivityManagerNative.broadcastStickyIntent(intent, null);
    }

然后只要你注册一个监听

Intent.ACTION_BATTERY_CHANGED

的广播就可以获得所有电池状态信息