我正在尝试从我的 android 平板电脑向 POS 打印机发送命令。我已经能够使基本连接正常工作,但是现在当我尝试将数据发送到打印机时,bulkTransfer 返回-1。请帮助我了解发生了什么。以下是从我进行所有数据传输的 android 站点获取的修改后的广播接收器。
private final BroadcastReceiver 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
if(device.getVendorId() != 1659)
return;
UsbInterface intf = device.getInterface(0);
UsbEndpoint endpoint = intf.getEndpoint(0);
int direction = endpoint.getDirection();
UsbDeviceConnection connection = mUsbManager.openDevice(device);
connection.claimInterface(intf, forceClaim);
bytes = new byte[]{27, 64};
//**This returns -1 always**
int ret = connection.bulkTransfer(endpoint, bytes, bytes.length, TIMEOUT);
if(ret < 0)
{
Log.d("WTF", "Error happened!");
}
else if(ret == 0)
{
Log.d("WTF", "No data transferred!");
}
else
{
Log.d("WTF", "success!");
}
}
}
else {
Log.d(TAG, "permission denied for device " + device);
}
}
}
}
};