Android USB通信弹出权限确认框

介绍

Android usb通信有两种模式：Host Mode和Accessory Mode；二者差异之处在于Host模式下，Android设备供电给usb设备；Accessory模式下usb设备供电给Android设备;官方示意图如下：

获取权限原理

1.调用UsbManager.requestPermission(UsbDevice device, PendingIntentpi)方法

/**
     * Requests temporary permission for the given package to access the device.
     * This may result in a system dialog being displayed to the user
     * if permission had not already been granted.
     * Success or failure is returned via the {@link android.app.PendingIntent} pi.
     * If successful, this grants the caller permission to access the device only
     * until the device is disconnected.
     *
     * The following extras will be added to pi:
     * 

     * 
 {@link #EXTRA_DEVICE} containing the device passed into this call
     * 
 {@link #EXTRA_PERMISSION_GRANTED} containing boolean indicating whether
     * permission was granted by the user
     * 
     *
     * @param device to request permissions for
     * @param pi PendingIntent for returning result
     */
    public void requestPermission(UsbDevice device, PendingIntent pi) {
        try {
            mService.requestDevicePermission(device, mContext.getPackageName(), pi);
        } catch (RemoteException e) {
            Log.e(TAG, "RemoteException in requestPermission", e);
        }
    }

在requestPermission方法里又调用了
mService.requestDevicePermission(device, mContext.getPackageName(), pi);
mService又是什么呢？看代码：

private final IUsbManager mService;

IUsbManager位于源码frameworks\base\core\java\android\hardware\usb目录下：

我们看到，IUsbManager文件是.aidl格式的，所以这里肯定使用了进程间通信。所以使用source insight全局搜索
IUsbManager字段，搜索结果如下：

了解过aidl的同学应该都知道，aidl是一种进程间通信的语言，包含客户端和服务端两个部分。一一查看各个类发现
UsbService代码如下：

public class UsbService extends IUsbManager.Stub {
    private static final String TAG = "UsbService";

    private final Context mContext;

    private UsbDeviceManager mDeviceManager;
    private UsbHostManager mHostManager;

    private final Object mLock = new Object();

    /** Map from {@link UserHandle} to {@link UsbSettingsManager} */
    @GuardedBy("mLock")
    private final SparseArray
            mSettingsByUser = new SparseArray();

    private UsbSettingsManager getSettingsForUser(int userId) {
        synchronized (mLock) {
            UsbSettingsManager settings = mSettingsByUser.get(userId);
            if (settings == null) {
                settings = new UsbSettingsManager(mContext, new UserHandle(userId));
                mSettingsByUser.put(userId, settings);
            }
            return settings;
        }
    }

    public UsbService(Context context) {
        mContext = context;

        final PackageManager pm = mContext.getPackageManager();
        if (pm.hasSystemFeature(PackageManager.FEATURE_USB_HOST)) {
            mHostManager = new UsbHostManager(context);
        }
        if (new File("/sys/class/android_usb").exists()) {
            mDeviceManager = new UsbDeviceManager(context);
        }

        setCurrentUser(UserHandle.USER_OWNER);

        final IntentFilter userFilter = new IntentFilter();
        userFilter.addAction(Intent.ACTION_USER_SWITCHED);
        userFilter.addAction(Intent.ACTION_USER_STOPPED);
        mContext.registerReceiver(mUserReceiver, userFilter, null, null);
    }

    private BroadcastReceiver mUserReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            final int userId = intent.getIntExtra(Intent.EXTRA_USER_HANDLE, -1);
            final String action = intent.getAction();
            if (Intent.ACTION_USER_SWITCHED.equals(action)) {
                setCurrentUser(userId);
            } else if (Intent.ACTION_USER_STOPPED.equals(action)) {
                synchronized (mLock) {
                    mSettingsByUser.remove(userId);
                }
            }
        }
    };

    private void setCurrentUser(int userId) {
        final UsbSettingsManager userSettings = getSettingsForUser(userId);
        if (mHostManager != null) {
            mHostManager.setCurrentSettings(userSettings);
        }
        if (mDeviceManager != null) {
            mDeviceManager.setCurrentSettings(userSettings);
        }
    }

    public void systemReady() {
        if (mDeviceManager != null) {
            mDeviceManager.systemReady();
        }
        if (mHostManager != null) {
            mHostManager.systemReady();
        }
    }

    /* Returns a list of all currently attached USB devices (host mdoe) */
    @Override
    public void getDeviceList(Bundle devices) {
        if (mHostManager != null) {
            mHostManager.getDeviceList(devices);
        }
    }

    /* Opens the specified USB device (host mode) */
    @Override
    public ParcelFileDescriptor openDevice(String deviceName) {
        if (mHostManager != null) {
            return mHostManager.openDevice(deviceName);
        } else {
            return null;
        }
    }

    /* returns the currently attached USB accessory (device mode) */
    @Override
    public UsbAccessory getCurrentAccessory() {
        if (mDeviceManager != null) {
            return mDeviceManager.getCurrentAccessory();
        } else {
            return null;
        }
    }

    /* opens the currently attached USB accessory (device mode) */
    @Override
    public ParcelFileDescriptor openAccessory(UsbAccessory accessory) {
        if (mDeviceManager != null) {
            return mDeviceManager.openAccessory(accessory);
        } else {
            return null;
        }
    }

    @Override
    public void setDevicePackage(UsbDevice device, String packageName, int userId) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        getSettingsForUser(userId).setDevicePackage(device, packageName);
    }

    @Override
    public void setAccessoryPackage(UsbAccessory accessory, String packageName, int userId) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        getSettingsForUser(userId).setAccessoryPackage(accessory, packageName);
    }

    @Override
    public boolean hasDevicePermission(UsbDevice device) {
        final int userId = UserHandle.getCallingUserId();
        return getSettingsForUser(userId).hasPermission(device);
    }

    @Override
    public boolean hasAccessoryPermission(UsbAccessory accessory) {
        final int userId = UserHandle.getCallingUserId();
        return getSettingsForUser(userId).hasPermission(accessory);
    }

    @Override
    public void requestDevicePermission(UsbDevice device, String packageName, PendingIntent pi) {
        final int userId = UserHandle.getCallingUserId();
        getSettingsForUser(userId).requestPermission(device, packageName, pi);
    }

    @Override
    public void requestAccessoryPermission(
            UsbAccessory accessory, String packageName, PendingIntent pi) {
        final int userId = UserHandle.getCallingUserId();
        getSettingsForUser(userId).requestPermission(accessory, packageName, pi);
    }

    @Override
    public void grantDevicePermission(UsbDevice device, int uid) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        final int userId = UserHandle.getUserId(uid);
        getSettingsForUser(userId).grantDevicePermission(device, uid);
    }

    @Override
    public void grantAccessoryPermission(UsbAccessory accessory, int uid) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        final int userId = UserHandle.getUserId(uid);
        getSettingsForUser(userId).grantAccessoryPermission(accessory, uid);
    }

    @Override
    public boolean hasDefaults(String packageName, int userId) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        return getSettingsForUser(userId).hasDefaults(packageName);
    }

    @Override
    public void clearDefaults(String packageName, int userId) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        getSettingsForUser(userId).clearDefaults(packageName);
    }

    @Override
    public void setCurrentFunction(String function, boolean makeDefault) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        if (mDeviceManager != null) {
            mDeviceManager.setCurrentFunctions(function, makeDefault);
        } else {
            throw new IllegalStateException("USB device mode not supported");
        }
    }

    @Override
    public void setMassStorageBackingFile(String path) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        if (mDeviceManager != null) {
            mDeviceManager.setMassStorageBackingFile(path);
        } else {
            throw new IllegalStateException("USB device mode not supported");
        }
    }

    @Override
    public void allowUsbDebugging(boolean alwaysAllow, String publicKey) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        mDeviceManager.allowUsbDebugging(alwaysAllow, publicKey);
    }

    @Override
    public void denyUsbDebugging() {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        mDeviceManager.denyUsbDebugging();
    }

    @Override
    public void dump(FileDescriptor fd, PrintWriter writer, String[] args) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.DUMP, TAG);
        final IndentingPrintWriter pw = new IndentingPrintWriter(writer, "  ");

        pw.println("USB Manager State:");
        if (mDeviceManager != null) {
            mDeviceManager.dump(fd, pw);
        }
        if (mHostManager != null) {
            mHostManager.dump(fd, pw);
        }

        synchronized (mLock) {
            for (int i = 0; i < mSettingsByUser.size(); i++) {
                final int userId = mSettingsByUser.keyAt(i);
                final UsbSettingsManager settings = mSettingsByUser.valueAt(i);
                pw.increaseIndent();
                pw.println("Settings for user " + userId + ":");
                settings.dump(fd, pw);
                pw.decreaseIndent();
            }
        }
        pw.decreaseIndent();
    }
}

所以aidl通信的服务端是UsbService，查看requestDevicePermission方法：

@Override
    public void requestDevicePermission(UsbDevice device, String packageName, PendingIntent pi) {
        final int userId = UserHandle.getCallingUserId();
        getSettingsForUser(userId).requestPermission(device, packageName, pi);
    }

我们继续查找getSettingsForUser方法：

private UsbSettingsManager getSettingsForUser(int userId) {
        synchronized (mLock) {
            UsbSettingsManager settings = mSettingsByUser.get(userId);
            if (settings == null) {
                settings = new UsbSettingsManager(mContext, new UserHandle(userId));
                mSettingsByUser.put(userId, settings);
            }
            return settings;
        }
    }

这个方法返回了一个UsbSettingsManager实例，跳转到这个类中，找到requestPermission方法：

public void requestPermission(UsbDevice device, String packageName, PendingIntent pi) {
      Intent intent = new Intent();

        // respond immediately if permission has already been granted
      if (hasPermission(device)) {
            intent.putExtra(UsbManager.EXTRA_DEVICE, device);
            intent.putExtra(UsbManager.EXTRA_PERMISSION_GRANTED, true);
            try {
                pi.send(mUserContext, 0, intent);
            } catch (PendingIntent.CanceledException e) {
                if (DEBUG) Slog.d(TAG, "requestPermission PendingIntent was cancelled");
            }
            return;
        }

        // start UsbPermissionActivity so user can choose an activity
        intent.putExtra(UsbManager.EXTRA_DEVICE, device);
        requestPermissionDialog(intent, packageName, pi);
    }

首先调用hasPermission方法，判断该应用是否已经获得usb权限

 public boolean hasPermission(UsbDevice device) {
        synchronized (mLock) {
            SparseBooleanArray uidList = mDevicePermissionMap.get(device.getDeviceName());
            if (uidList == null) {
                return false;
            }
            return uidList.get(Binder.getCallingUid());
        }
    }

SparseBooleanArray uidList = mDevicePermissionMap.get(device.getDeviceName());查询获得了该usb设备访问
权限的应用列表，如果uidList为空，说明当前没有应用获得该usb设备的权限，否则调用get方法

/**
     * Gets the boolean mapped from the specified key, or false
     * if no such mapping has been made.
     */
    public boolean get(int key) {
        return get(key, false);
    }

执行完if（hasPermission）判断后，紧接着调用了requestPermissionDialog(intent, packageName, pi);方法

private void requestPermissionDialog(Intent intent, String packageName, PendingIntent pi) {
        final int uid = Binder.getCallingUid();

        // compare uid with packageName to foil apps pretending to be someone else
        try {
            ApplicationInfo aInfo = mPackageManager.getApplicationInfo(packageName, 0);
            if (aInfo.uid != uid) {
                throw new IllegalArgumentException("package " + packageName +
                        " does not match caller's uid " + uid);
            }
        } catch (PackageManager.NameNotFoundException e) {
            throw new IllegalArgumentException("package " + packageName + " not found");
        }

        long identity = Binder.clearCallingIdentity();
        intent.setClassName("com.android.systemui",
                "com.android.systemui.usb.UsbPermissionActivity");
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.putExtra(Intent.EXTRA_INTENT, pi);
        intent.putExtra("package", packageName);
        intent.putExtra(Intent.EXTRA_UID, uid);
        try {
            mUserContext.startActivityAsUser(intent, mUser);
        } catch (ActivityNotFoundException e) {
            Slog.e(TAG, "unable to start UsbPermissionActivity");
        } finally {
            Binder.restoreCallingIdentity(identity);
        }
    }

这个方法主要是跳转到UsbPermissionActivity中，UsbPermissionActivity就是系统弹出的权限确认框，效果图如下

所以aidl通信的服务端是UsbService，查看requestDevicePermission方法：SparseBooleanArray uidList = mDevicePermissionMap.get(device.getDeviceName());

代码如下：

/*
 * Copyright (C) 2011 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.usb;


import android.app.Activity;
import android.app.AlertDialog;
import android.app.PendingIntent;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.hardware.usb.IUsbManager;
import android.hardware.usb.UsbDevice;
import android.hardware.usb.UsbAccessory;
import android.hardware.usb.UsbManager;
import android.os.Bundle;
import android.os.IBinder;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.os.UserHandle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.TextView;


import com.android.internal.app.AlertActivity;
import com.android.internal.app.AlertController;


import com.android.systemui.R;


public class UsbPermissionActivity extends AlertActivity
        implements DialogInterface.OnClickListener, CheckBox.OnCheckedChangeListener {


    private static final String TAG = "UsbPermissionActivity";


    private CheckBox mAlwaysUse;
    private TextView mClearDefaultHint;
    private UsbDevice mDevice;
    private UsbAccessory mAccessory;
    private PendingIntent mPendingIntent;
    private String mPackageName;
    private int mUid;
    private boolean mPermissionGranted;
    private UsbDisconnectedReceiver mDisconnectedReceiver;


    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);


       Intent intent = getIntent();
        mDevice = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
        mAccessory = (UsbAccessory)intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);
        mPendingIntent = (PendingIntent)intent.getParcelableExtra(Intent.EXTRA_INTENT);
        mUid = intent.getIntExtra(Intent.EXTRA_UID, -1);
        mPackageName = intent.getStringExtra("package");


        PackageManager packageManager = getPackageManager();
        ApplicationInfo aInfo;
        try {
            aInfo = packageManager.getApplicationInfo(mPackageName, 0);
        } catch (PackageManager.NameNotFoundException e) {
            Log.e(TAG, "unable to look up package name", e);
            finish();
            return;
        }
        String appName = aInfo.loadLabel(packageManager).toString();


        final AlertController.AlertParams ap = mAlertParams;
        ap.mIcon = aInfo.loadIcon(packageManager);
        ap.mTitle = appName;
        if (mDevice == null) {
            ap.mMessage = getString(R.string.usb_accessory_permission_prompt, appName);
            mDisconnectedReceiver = new UsbDisconnectedReceiver(this, mAccessory);
        } else {
            ap.mMessage = getString(R.string.usb_device_permission_prompt, appName);
            mDisconnectedReceiver = new UsbDisconnectedReceiver(this, mDevice);
        }
        ap.mPositiveButtonText = getString(android.R.string.ok);
        ap.mNegativeButtonText = getString(android.R.string.cancel);
        ap.mPositiveButtonListener = this;
        ap.mNegativeButtonListener = this;


        LayoutInflater inflater = (LayoutInflater)getSystemService(
                Context.LAYOUT_INFLATER_SERVICE);
        ap.mView = inflater.inflate(com.android.internal.R.layout.always_use_checkbox, null);
        mAlwaysUse = (CheckBox)ap.mView.findViewById(com.android.internal.R.id.alwaysUse);
        if (mDevice == null) {
            mAlwaysUse.setText(R.string.always_use_accessory);
        } else {
            mAlwaysUse.setText(R.string.always_use_device);
        }
        mAlwaysUse.setOnCheckedChangeListener(this);
        mClearDefaultHint = (TextView)ap.mView.findViewById(
                                                    com.android.internal.R.id.clearDefaultHint);
        mClearDefaultHint.setVisibility(View.GONE);


        setupAlert();
		
    
    }


    @Override
    public void onDestroy() {
        IBinder b = ServiceManager.getService(USB_SERVICE);
        IUsbManager service = IUsbManager.Stub.asInterface(b);


        // send response via pending intent
        Intent intent = new Intent();
        try {
            if (mDevice != null) {
                intent.putExtra(UsbManager.EXTRA_DEVICE, mDevice);
                if (mPermissionGranted) {
                    service.grantDevicePermission(mDevice, mUid);
                  //  if (mAlwaysUse.isChecked()) 
					{
                        final int userId = UserHandle.getUserId(mUid);
                        service.setDevicePackage(mDevice, mPackageName, userId);
                    }
                }
            }
            if (mAccessory != null) {
                intent.putExtra(UsbManager.EXTRA_ACCESSORY, mAccessory);
                if (mPermissionGranted) {
                    service.grantAccessoryPermission(mAccessory, mUid);
                   // if (mAlwaysUse.isChecked()) 
					{
                        final int userId = UserHandle.getUserId(mUid);
                        service.setAccessoryPackage(mAccessory, mPackageName, userId);
                    }
                }
            }
            intent.putExtra(UsbManager.EXTRA_PERMISSION_GRANTED, mPermissionGranted);
            mPendingIntent.send(this, 0, intent);
        } catch (PendingIntent.CanceledException e) {
            Log.w(TAG, "PendingIntent was cancelled");
        } catch (RemoteException e) {
            Log.e(TAG, "IUsbService connection failed", e);
        }


        if (mDisconnectedReceiver != null) {
            unregisterReceiver(mDisconnectedReceiver);
        }
        super.onDestroy();
    }


    public void onClick(DialogInterface dialog, int which) {
        if (which == AlertDialog.BUTTON_POSITIVE) {
            mPermissionGranted = true;
        }
        finish();
    }


    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if (mClearDefaultHint == null) return;


        if(isChecked) {
            mClearDefaultHint.setVisibility(View.VISIBLE);
        } else {
            mClearDefaultHint.setVisibility(View.GONE);
        }
    }
}

在onCreate方法里弹出权限确认框，如果用户点击“确定”，则mPermissionGranted = true;然后调用finish，
进入onDestroy方法调了 service.grantDevicePermission(mDevice, mUid);我们再继续进入UsbService中查看
grantDevicePermission方法

@Override
    public void grantDevicePermission(UsbDevice device, int uid) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);
        final int userId = UserHandle.getUserId(uid);
        getSettingsForUser(userId).grantDevicePermission(device, uid);
    }

getSettingForUser方法返回的是USBSettingManager实例，我们进入该类中，查找grantDevicePermission方法：

public void grantDevicePermission(UsbDevice device, int uid) {
        synchronized (mLock) {
            String deviceName = device.getDeviceName();
            SparseBooleanArray uidList = mDevicePermissionMap.get(deviceName);
            if (uidList == null) {
                uidList = new SparseBooleanArray(1);
                mDevicePermissionMap.put(deviceName, uidList);
            }
            uidList.put(uid, true);
        }
    }

代码的主要功能是将应用的uid和usb设备建立映射关系，然后存储起来。还记得上面的hasPermission方法吗

public boolean hasPermission(UsbDevice device) {
        synchronized (mLock) {
            SparseBooleanArray uidList = mDevicePermissionMap.get(device.getDeviceName());
            if (uidList == null) {
                return false;
            }
            return uidList.get(Binder.getCallingUid());
        }
    }

这两个方法刚好一个是存uid和usb的映射关系，一个是读取uid和usb的映射关系，判断是否该uid对应的应用已具有
该usb设备的权限。

以上就是usb权限申请的逻辑，总结一下如下：

1.UsbManager.requestPermission(UsbDevice device, PendingIntent pi),在此方法中调用2
2.UsbService.requestDevicePermission(UsbDevice device, String packageName, PendingIntent pi)，在此方法中调用3
3.UsbSettingManager.requestPermission(UsbDevice device, String packageName, PendingIntent pi)，在此方法中启动UsbPermissionActivity
4.UsbPermissionActivity，在此方法中
5.UsbService.grantDevicePermission(UsbDevice device, int uid)
5.UsbSettingManager.grantDevicePermission(UsbDevice device, int uid)


如果应用想要自动获取usb权限，只要在UsbPermissionActivity中处理就可以了。