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我正在尝试连接到 USB 打印机并从中打印数据。我正在使用下面的代码来执行此操作，以下事情正在发生。

  • 我从手机启动应用程序 - 应用程序打开并显示带有“打印”按钮的屏幕。

  • 当我通过 OTG 电缆连接打印机 USB 时，弹出权限对话框，我在其中选择允许权限。

  • 现在我按下“打印”按钮，我看到了放在代码中的祝酒词

    1>“设备数量：1”

    2>“设备已连接”

    3>“printdata.getBytes().length ====>”

  • 打印机显示“正在接收数据”，但之后它什么也不做。一切正常，但问题是没有打印

    public class USBAdapter {

private UsbManager mUsbManager;
private UsbDevice mDevice;
UsbDevice printer = null;
private PendingIntent mPermissionIntent;
UsbDeviceConnection connection;
String TAG = "USB";
private static final String ACTION_USB_PERMISSION =  "com.android_usb_printer.USB_PERMISSION";


public USBAdapter() {
}

public void createConn(Context context) {
    mUsbManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
    HashMap<String, UsbDevice> deviceList = mUsbManager.getDeviceList();
    if (deviceList.size() <= 0) {
        Log.i("Info", "No device found");
        Toast.makeText(context, "No device found", Toast.LENGTH_SHORT).show();
    } else {
        Log.i("Info", "Number of device : " + deviceList.size());
        Toast.makeText(context, "Number of device : " + deviceList.size(), Toast.LENGTH_SHORT).show();

    }
    Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();

    mPermissionIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
    while (deviceIterator.hasNext()) {
        mDevice = deviceIterator.next();
        Log.i("info", "Vendor id : " + mDevice.getVendorId());
        Log.i("info", "Product id : " + mDevice.getProductId());
        Log.i("info", "Device  name : " + mDevice.getDeviceName());
        Log.i("info", "Device class : " + mDevice.getClass().getName());
        Log.i("info", "Device protocol: " + mDevice.getDeviceProtocol());
        Log.i("info", "Device subclass : " + mDevice.getDeviceSubclass());

    }
    /*final String ACTION_USB_PERMISSION = "com.android_usb_printer.USB_PERMISSION";
    mPermissionIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
    IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
    context.registerReceiver(mUsbReceiver, filter);*/
}

private final BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {

    public void onReceive(Context context, Intent intent) {
        System.out.println("<=======Onreceived=======>");
        String action = intent.getAction();
        if (ACTION_USB_PERMISSION.equals(action)) {
            synchronized (this) {
                mDevice = (UsbDevice) intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                Toast.makeText(context, "mDevice ====>"+mDevice, Toast.LENGTH_SHORT).show();
                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                    if (mDevice != null) {
                        //call method to set up device communication
                    }
                } else {
                    Log.d(TAG, "permission denied for device " + mDevice);
                }
            }
        }
    }
};

@SuppressLint("NewApi")
public void printMessage(final Context context, String msg) {
    // TODO Auto-generated method stub
    final String printdata = msg;
    final UsbEndpoint mEndpointBulkOut;
    if (mUsbManager.hasPermission(mDevice)) {
        UsbInterface intf ;
        for(int i = 0; i < mDevice.getInterfaceCount(); i++){
            intf = mDevice.getInterface(i);
            if(intf.getInterfaceClass() == UsbConstants.USB_CLASS_PRINTER){
                printer = mDevice;

                UsbEndpoint ep = intf.getEndpoint(i);
                int b;
                if (ep.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
                    if (ep.getDirection() == UsbConstants.USB_DIR_OUT) {
                        mEndpointBulkOut = ep;
                        connection = mUsbManager.openDevice(printer);
                        if (connection != null) {
                            Log.e("Connection:", " connected");
                            Toast.makeText(context, "Device connected", Toast.LENGTH_SHORT).show();
                        }

                        Toast.makeText(context, "printdata.getBytes().length ====>"+printdata.getBytes().length, Toast.LENGTH_SHORT).show();

                        boolean forceClaim = true;
                        connection.claimInterface(intf, forceClaim);
                        //Integer res = connection.bulkTransfer(mEndpointBulkOut, printdata.getBytes(), printdata.getBytes().length, 10000);
                        new Thread(new Runnable() {
                            @Override
                            public void run() {
                                // TODO Auto-generated method stub
                                Log.i("Thread:", "in run thread");
                                byte[] bytes = printdata.getBytes();
                                int b = connection.bulkTransfer(mEndpointBulkOut, bytes, bytes.length, 100000);
                                Log.i("Return Status", "b-->" + b);
                            }
                        }).start();
                        connection.releaseInterface(intf);
                        break;
                    }
                }
            }
        }
    } else {
        mUsbManager.requestPermission(mDevice, mPermissionIntent);
        Toast.makeText(context, "Device have no permission", Toast.LENGTH_SHORT).show();
    }
}

@SuppressLint("NewApi")
public void closeConnection(Context context) {
    BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();

            if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
                UsbDevice device = (UsbDevice) intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                if (device != null) {
                    Toast.makeText(context, "Device closed", Toast.LENGTH_SHORT).show();
                    connection.close();
                }
            }
        }
    };
}
}

printMessage()正在从我出错的MainActivityonclick()点中的打印按钮调用。谢谢。

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