serialPort.getInputStream() causes android app to crash.

[nancysemwal]

Details:

Android Studio Arctic Fox

Ubuntu 18.04.4 LTS

Samsung phone with Android 11

I am unable to obtain an input stream from a serial port.

`public class MainActivity extends AppCompatActivity {

public static final String EXTRA_MESSAGE = "HELLO";
private static final String TAG = "mainActivity";
private UsbManager manager;
private HashMap<String, UsbDevice> deviceList;
private UsbDevice device;
private UsbDeviceConnection connection;
private UsbSerialDevice serial;
private MavlinkConnection mavConn;
private MavlinkMessage message;
private SerialInputStream input;
private SerialOutputStream output;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)

public void onConnect(View view) throws IOException {
   manager = (UsbManager) getSystemService(Context.USB_SERVICE);
   deviceList = manager.getDeviceList();
   if(deviceList.isEmpty()) {
       new AlertDialog.Builder(this)
               .setTitle("Error!")
               .setMessage("no devices connected")
               .show();
       return;
   }
   else {
       TextView textView = findViewById(R.id.textView);
       device = (UsbDevice) getIntent().getParcelableExtra(UsbManager.EXTRA_DEVICE);
       connection = manager.openDevice(device);
       serial = UsbSerialDevice.createUsbSerialDevice(device, connection);
       if(serial != null){
           if(serial.open()) {
               serial.setBaudRate(57600);
           }
           else {
               new AlertDialog.Builder(this)
                       .setTitle("Error!")
                       .setMessage("Port not open")
                       .show();
               return;
           }
       }
       else {
           new AlertDialog.Builder(this)
                   .setTitle("Error!")
                   .setMessage("Serial is null")
                   .show();
           return;
       }
      // ************************ all fine till here. displays deviceID on phone ************************************
       textView.setText(Integer.toString(serial.getDeviceId()));  
       input = serial.getInputStream(); //crashes right here.
       if(input != null) {
           textView.setText("got stream");
       }
       else {
           new AlertDialog.Builder(this)
                   .setTitle("Error!")
                   .setMessage("Null stream")
                   .show();
           return;
       }
       /* ******************cannot test this piece of code due to lack of input stream**********************
           output = serial.getOutputStream();
            mavConn = MavlinkConnection.create(input, output);*/
       connection.close();
   }
}

private UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() {

    @Override
    public void onReceivedData(byte[] arg0)
    {

        /*cannot test this piece of code due to lack of input stream
    while (true) {
            try {
                while (!((message = mavConn.next()) != null)) {
                    if(message.getPayload() instanceof Heartbeat) {
                        textView.setText(message.getPayload().toString());
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }*/
    }

};

}`

When the app is installed and run on my phone as a USB host with a Pixhawk microcontroller attached, I am able to view the serial port details like deviceID, baud rate, etc in the textView, but just when I do serial.getInputStream(), the app crashes.

I have no method to know why it crashes. I just get the "App keeps stopping" error message. I cannot view the log messages via Logcat since I'm not connected to my PC. I also cannot debugg over WiFi because I do majority of my work in my office where I use Ethernet LAN, not WiFi.

What are my options? Is debugging over WiFi the only way? Can't I print the logs to some text file on my phone and then view them later?

[nancysemwal]

The app was crashing because the serial.getInputStream() was getting done in async mode, while the library provides InputStream in sync mode only.