我寫了一個簡單的應用程序,通過USB將命令發送到連接到Android 4.0平板電腦的USB打印機.出于某種原因,我無法獲得聲明接口和打開連接的權限.這是相關的代碼：

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 deviceList = mUsbManager.getDeviceList();

for (HashMap.Entry 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;

}

}

}

這是清單的相關部分：

package="com.demo.printerDemo"

android:versionCode="1"

android:versionName="1.0" >

android:minSdkVersion="14"

android:targetSdkVersion="17" />

我已經配置了設備,以便在連接打印機時啟動我的應用程序,并在枚舉期間找到設備(onResume())并調用權限請求.但是,無論出于何種原因,我從未看到“請求權限”對話框(我在網上看過它的截圖),也沒有看到onReceive().任何想法為什么會這樣？

解決方法:

1)為什么你有兩個成員ACTION_USB_PERMISSION聲明？

2)在onCreate()中嘗試像這樣注冊你的Intent,也許有區別：

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中的錯誤(http://code.google.com/p/android/issues/detail?id=25703),我不確定是否曾調用過ACTION_USB_ACCESSORY_ATTACHED操作.嘗試在AndroidManifest.xml中添加以下內容：

標簽：host,android,printing,usb

來源： https://codeday.me/bug/20191008/1874180.html

總結

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