Android USB 权限对话框从不出现

Question

我编写了一个简单的应用程序，用于向通过 USB 连接到 Android 4.0 平板电脑的 USB 打印机发送命令。出于某种原因，我无法通过获得声明接口(interface)和打开连接的权限。这是相关代码:

public class TestPrintActivity extends Activity {

private UsbManager mUsbManager;
private UsbDevice mDevice;
private UsbDeviceConnection mConnection;
private UsbInterface mInterface;
private UsbEndpoint mBulkIn;
private UsbEndpoint mBulkOut;
private static final String ACTION_USB_PERMISSION =
        "com.demo.xprinter.USB_PERMISSION";
private PendingIntent mPermissionIntent;
private BroadcastReceiver mUsbReceiver; 

@Override

private static final String ACTION_USB_PERMISSION =
        "com.demo.printerDemo.USB_PERMISSION";



protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test_print);

    mUsbManager = (UsbManager)getSystemService(Context.USB_SERVICE);

    mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
    IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
    filter.addAction(UsbManager.ACTION_USB_ACCESSORY_DETACHED);
    filter.addAction(UsbManager.ACTION_USB_ACCESSORY_ATTACHED);
    registerReceiver(mUsbReceiver, filter);

    mUsbReceiver = new BroadcastReceiver() {

        public void onReceive(Context context, Intent intent) {

            String action = intent.getAction();
            if (ACTION_USB_PERMISSION.equals(action)) {
                synchronized (this) {
                    UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                    if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                        if(device != null){
                          //call method to set up device communication
                            openPort(device);
                       }
                    } 
                    else {
                        Toast.makeText(getApplicationContext(), "Denied!", Toast.LENGTH_SHORT).show();
                    }
                }
            }
        }
    };

}

public void onResume() {
    super.onResume();

    HashMap<String,UsbDevice> deviceList = mUsbManager.getDeviceList();

    for (HashMap.Entry<String,UsbDevice> entry : deviceList.entrySet()) {
          UsbDevice aDevice = entry.getValue();
          if ((aDevice.getProductId() == 8965) && (aDevice.getVendorId() == 1659) ){

              if (mUsbManager.hasPermission(aDevice))
                openPort(aDevice);
              else
                mUsbManager.requestPermission(aDevice, mPermissionIntent);
              break;
          }
        }


}

这是 list 的相关部分:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.demo.printerDemo"
    android:versionCode="1"
    android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="14"
    android:targetSdkVersion="17" />
<uses-feature android:name="android.hardware.usb.host"/>

我已配置设备，以便在连接打印机时启动我的应用程序，并在枚举期间找到设备 (onResume()) 并调用权限请求。但是，无论出于何种原因，我从未看到“请求权限”对话框(我在网上看到过它的屏幕截图)，也从未调用过 onReceive()。任何想法为什么会发生这种情况？

Answer 1

1) 为什么要声明两个成员 ACTION_USB_PERMISSION？

2) 在 onCreate() 中尝试像这样注册您的 Intent，也许有区别:

IntentFilter filter = new IntentFilter();
filter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);
filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
    filter.addAction(ACTION_USB_PERMISSION);
context.registerReceiver(usbReceiver, filter);

3) 由于 Android (http://code.google.com/p/android/issues/detail?id=25703) 中的错误，我不确定是否调用了 ACTION_USB_ACCESSORY_ATTACHED 操作。尝试在您的 AndroidManifest.xml 中添加以下内容:

    <activity ...>
 <intent-filter >
                <action android:name="android.intent.action.MAIN" />                
                <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
                <action android:name="android.hardware.usb.action.USB_DEVICE_DETACHED" />
                <meta-data android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" android:resource="@xml/device_filter"/>
                <category android:name="android.intent.category.HOME" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
</activity>