Print usb android

I am trying to print a String through a USB printer.

I use the following method:

public void printMessage(Context context,String msg) {
    // TODO Auto-generated method stub
    final String printdata = msg;
    final UsbEndpoint mEndpointBulkOut;
    if (mUsbManager.hasPermission(mDevice)){
        UsbInterface intf = mDevice.getInterface(0);
        for (int i = 0; i < intf.getEndpointCount(); i++) {
               UsbEndpoint ep = intf.getEndpoint(i);
             if (ep.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
                   if (ep.getDirection() == UsbConstants.USB_DIR_OUT) {
                       mEndpointBulkOut = ep;
                           connection = mUsbManager.openDevice(mDevice);
                       if(connection!=null)
                       {
                         Log.e("Connection:"," connected");
                         Toast.makeText(context, "Device connected", 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();
    }
}

The problem here sche mDevice is null. The method where you supposedly give value to mDevice is:

private final BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        intent = new Intent();
            if (ACTION_USB_PERMISSION.equals(action)) {
                synchronized (this) {
                    mDevice = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                        if(mDevice != null){

                       }
                    }
                    else {
                        Log.d(TAG, "Permiso denegado " + mDevice);
                    }
                }
        }
    }
};

Thanks. Greetings.