android关于硬件USB权限综合解读

前言

这篇是以极大疑惑为驱动的文章，综合了大多数文章对USB权限申请的常规方法，及特殊操作。带着这样的疑惑来看这篇文章：为什么部分机型在硬件连接手机时没有任何的权限请求提示框呢？

1.常规申请

修改AndroidManifest.xml

<uses-feature android:name="android.hardware.usb.host" /> <uses-feature android:name="android.hardware.usb.accessory" />

在<actvity>主类添加

<activity android:name="MainActivity" android:exported="true" android:label="@string/title" android:screenOrientation="portrait" android:theme="@style/AppTheme.NoActionBar"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> <intent-filter> <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" /> </intent-filter> <meta-data android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" android:resource="@xml/device_filter" /> </activity>

 其中的@xml/device_filter在res中添加xml目录，并新建device_filter,并在其中添加以下代码，其中的设备号等参数需要自己对照USB设备的参数。

<?xml version="1.0" encoding="utf-8"?> <resources> <usb-device vendor-id="6790" product-id="29987" /> </resources>

 

2.主动申请

以上第一步就是对主动申请的准备工作，接下来进入主动申请的步骤

1.首先需要检测usb设备，并过滤intent

UsbManager mUsbManager; private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION"; private void tryGetUsbPermission(){ mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE); IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION); registerReceiver(mUsbPermissionActionReceiver, filter); PendingIntent mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0); //here do emulation to ask all connected usb device for permission for (final UsbDevice usbDevice : mUsbManager.getDeviceList().values()) { //add some conditional check if necessary //if(isWeCaredUsbDevice(usbDevice)){ if(mUsbManager.hasPermission(usbDevice)){ //if has already got permission, just goto connect it //that means: user has choose yes for your previously popup window asking for grant perssion for this usb device //and also choose option: not ask again //afterGetUsbPermission(usbDevice); }else{ //this line will let android popup window, ask user whether to allow this app to have permission to operate this usb device mUsbManager.requestPermission(usbDevice, mPermissionIntent); } //} } }

2.注册广播监听权限是否通过

private final BroadcastReceiver mUsbPermissionActionReceiver = new BroadcastReceiver() { public void onReceive(Context context, Intent intent) { String action = intent.getAction(); if (ACTION_USB_PERMISSION.equals(action)) { synchronized (this) { UsbDevice usbDevice = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE); if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) { //user choose YES for your previously popup window asking for grant perssion for this usb device if(null != usbDevice){ //do something after get usbDevice } } else { //user choose NO for your previously popup window asking for grant perssion for this usb device Toast.makeText(context, String.valueOf("Permission denied for device" + usbDevice), Toast.LENGTH_LONG).show(); } } } } };

 以上就是动态申请的全部内容。

3.无感申请

但是步骤二对多数场景的使用特别不友好，特别是远程维护的安卓设备在每次断电之后都会重新加载usb设备，此时弹框将阻碍设备的正常运行。这时就需要绕开弹框，从framework层着手。

找到源码/android/frameworks/base/packages/SystemUI/src/com/android/systemui/usb/UsbPermissionActivity.java

//setupAlert();//不使用窗口 mPermissionGranted = true; finish();

 注释掉设置弹框的代码，当然也可以按包名定制是否需要弹框确认。

4.Android SDK适配

如果，按照常规操作，并不能顺利地申请到usb权限，你会有怎样的思考呢？现象就是部分机型上有弹框出现，部分机型上没有弹框出现。这个问题的解答，直到阅读到这样一篇文章，如下

而给出的解决方法就是将android项目中的所有targetSdkVersion统一为27及以下，注意仅仅是targetSDKVersion，其他的设置可以不变，而究竟为什么要这样做，我个人认为可能是官方的刻意限制，不同版本的SDK在usb权限申请弹框上有差异。