Bluetooth connection in Android > 4.1.2

Question

I wrote the following activity to connect my Nexus 7 with Arduino, to simply exchange 0 and 1 to switch on and off a led. I took example from here: http://developer.android.com/guide/topics/connectivity/bluetooth.html#ManagingAConnection and also recalled here: How to connect with paired Bluetooth device programmatic in Android?

but it almost never connects or if it connects does not display UI. Almost all the time the app crashes when paused or resumed.

I'm sure there is something wrong in how threads are written, but cannot understand where.

package com.example.bluetooth3;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;
import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

    private static final String TAG = "bluetooth2";

    Button btnOn, btnOff;
    TextView txtArduino;
    Handler h;

    final int receivedMessage = 1;      // Status  for Handler
    private BluetoothAdapter btAdapter = null;
    private BluetoothSocket btSocket = null;
    private StringBuilder sb = new StringBuilder();

    private ConnectedThread mConnectedThread;
    private ConnectThread mConnectThread;

    // SPP UUID service
    private static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");

    // MAC-address of Bluetooth module (you must edit this line)
    private static String address = "00:06:66:60:1D:09";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnOn = (Button) findViewById(R.id.btnOn);                  // button LED ON
        btnOff = (Button) findViewById(R.id.btnOff);                // button LED OFF
        txtArduino = (TextView) findViewById(R.id.txtArduino);      // for display the received data from the Arduino

        h = new Handler() {
            public void handleMessage(android.os.Message msg) {
                switch (msg.what) {
                case receivedMessage:                                                   // if receive massage
                    byte[] readBuf = (byte[]) msg.obj;
                    String strIncom = new String(readBuf, 0, msg.arg1);                 // create string from bytes array
                    sb.append(strIncom);                                                // append string
                    int endOfLineIndex = sb.indexOf("\r\n");                            // determine the end-of-line
                    if (endOfLineIndex > 0) {                                           // if end-of-line,
                        String sbprint = sb.substring(0, endOfLineIndex);               // extract string
                        sb.delete(0, sb.length());                                      // and clear
                        txtArduino.setText("Data from Arduino: " + sbprint);            // update TextView
                        btnOff.setEnabled(true);
                        btnOn.setEnabled(true); 
                    }
                    //Log.d(TAG, "...String:"+ sb.toString() +  "Byte:" + msg.arg1 + "...");
                    break;
                }
            };
        };

        btAdapter = BluetoothAdapter.getDefaultAdapter();       // get Bluetooth adapter

        btnOn.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                btnOn.setEnabled(false);
                mConnectedThread.write("1");    // Send "1" via Bluetooth
                //Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
            }
        });

        btnOff.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                btnOff.setEnabled(false);  
                mConnectedThread.write("0");    // Send "0" via Bluetooth
                //Toast.makeText(getBaseContext(), "Turn off LED", Toast.LENGTH_SHORT).show();
            }
        });     
    }

    @Override
    public void onResume() {
        super.onResume();

        Log.d(TAG, "...onResume - try connect...");
        checkBTState();
        // Set up a pointer to the remote node using it's address.
        BluetoothDevice device = btAdapter.getRemoteDevice(address);

        mConnectThread=new ConnectThread(device);
        mConnectThread.run();

    }

    @Override
    public void onPause() {
        super.onPause();

        Log.d(TAG, "...In onPause()...");

        //try     {
        //  btSocket.close();
        //} catch (IOException e2) {
        //  errorExit("Fatal Error", "In onPause() and failed to close socket." + e2.getMessage() + ".");
        //}
        mConnectedThread.cancel();
    }

    private void checkBTState() {
        // Check for Bluetooth support and then check to make sure it is turned on
        // Emulator doesn't support Bluetooth and will return null
        if(btAdapter==null) { 
            errorExit("Fatal Error", "Bluetooth not support");
        } else {
            if (btAdapter.isEnabled()) {
                Log.d(TAG, "...Bluetooth ON...");
            } else {
                //Prompt user to turn on Bluetooth
                Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                startActivityForResult(enableBtIntent, 1);
            }
        }
    }

    private void errorExit(String title, String message){
        Toast.makeText(getBaseContext(), title + " - " + message, Toast.LENGTH_LONG).show();
        finish();
    }

    private class ConnectThread extends Thread {
        private final BluetoothSocket mmSocket;
        private final BluetoothDevice mmDevice;

        public ConnectThread(BluetoothDevice device) {
            // Use a temporary object that is later assigned to mmSocket,
            // because mmSocket is final
            BluetoothSocket tmp = null;
            mmDevice = device;

            // Get a BluetoothSocket to connect with the given BluetoothDevice
            try {
                // MY_UUID is the app's UUID string, also used by the server code
                tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
            } catch (IOException e) { }
            mmSocket = tmp;
        }

        public void run() {
            //android.os.Debug.waitForDebugger();
            // Cancel discovery because it will slow down the connection
            Log.d(TAG, "prova");
            btAdapter.cancelDiscovery();

            try {
                // Connect the device through the socket. This will block
                // until it succeeds or throws an exception
                mmSocket.connect();
            } catch (IOException connectException) {
                // Unable to connect; close the socket and get out
                try {
                    mmSocket.close();
                } catch (IOException closeException) { }
                return;
            }

            // Do work to manage the connection (in a separate thread)
            mConnectedThread=new ConnectedThread(mmSocket);
            mConnectedThread.run();
        }

        /** Will cancel an in-progress connection, and close the socket */
        public void cancel() {
            try {
                mmSocket.close();
            } catch (IOException e) { }
        }
    }

    private class ConnectedThread extends Thread {
        private final BluetoothSocket mmSocket;
        private final InputStream mmInStream;
        private final OutputStream mmOutStream;

        public ConnectedThread(BluetoothSocket socket) {
            mmSocket = socket;
            InputStream tmpIn = null;
            OutputStream tmpOut = null;

            // Get the input and output streams, using temp objects because
            // member streams are final
            try {
                tmpIn = socket.getInputStream();
                tmpOut = socket.getOutputStream();
            } catch (IOException e) { }

            mmInStream = tmpIn;
            mmOutStream = tmpOut;
        }

        public void run() {
            //android.os.Debug.waitForDebugger();
            byte[] buffer = new byte[1024];  // buffer store for the stream
            int bytes; // bytes returned from read()

            // Keep listening to the InputStream until an exception occurs
            while (true) {
                try {
                    // Read from the InputStream
                    bytes = mmInStream.read(buffer);
                    // Send the obtained bytes to the UI Activity
                    h.obtainMessage(receivedMessage, bytes, -1, buffer)
                            .sendToTarget();
                } catch (IOException e) {
                    break;
                }
            }
        }

        /* Call this from the main activity to send data to the remote device */
        public void write(String message) {
            Log.d(TAG, "...Data to send: " + message + "...");
            byte[] msgBuffer = message.getBytes();
            try {
                mmOutStream.write(msgBuffer);
            } catch (IOException e) {
                Log.d(TAG, "...Error data send: " + e.getMessage() + "...");     
            }
        }

        /* Call this from the main Activity to shutdown the connection */
        public void cancel() {
            try {
                mmSocket.close();
            } catch (IOException e) { }
        }
    }

}

I also tried an other activity found here which works better but does not use separated thread to connect. But still has problems as far as it sometime crashes after resuming, specially if bluetooth is not connected, or it resumes properly but does not connect to the Arduino BT device.

package com.example.bluetooth2;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Method;
import java.util.UUID;

import com.example.bluetooth2.R;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private static final String TAG = "bluetooth2";

    Button btnOn, btnOff;
    TextView txtArduino;
    Handler h;

    final int RECIEVE_MESSAGE = 1;      // Status  for Handler
    private BluetoothAdapter btAdapter = null;
    private BluetoothSocket btSocket = null;
    private StringBuilder sb = new StringBuilder();

    private ConnectedThread mConnectedThread;

    // SPP UUID service
    private static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");

    // MAC-address of Bluetooth module (you must edit this line)
    private static String address = "00:06:66:60:1D:09";

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        btnOn = (Button) findViewById(R.id.btnOn);                  // button LED ON
        btnOff = (Button) findViewById(R.id.btnOff);                // button LED OFF
        txtArduino = (TextView) findViewById(R.id.txtArduino);      // for display the received data from the Arduino

        h = new Handler() {
            public void handleMessage(android.os.Message msg) {
                switch (msg.what) {
                case RECIEVE_MESSAGE:                                                   // if receive massage
                    byte[] readBuf = (byte[]) msg.obj;
                    String strIncom = new String(readBuf, 0, msg.arg1);                 // create string from bytes array
                    sb.append(strIncom);                                                // append string
                    int endOfLineIndex = sb.indexOf("\r\n");                            // determine the end-of-line
                    if (endOfLineIndex > 0) {                                           // if end-of-line,
                        String sbprint = sb.substring(0, endOfLineIndex);               // extract string
                        sb.delete(0, sb.length());                                      // and clear
                        txtArduino.setText("Data from Arduino: " + sbprint);            // update TextView
                        btnOff.setEnabled(true);
                        btnOn.setEnabled(true); 
                    }
                    //Log.d(TAG, "...String:"+ sb.toString() +  "Byte:" + msg.arg1 + "...");
                    break;
                }
            };
        };

        btAdapter = BluetoothAdapter.getDefaultAdapter();       // get Bluetooth adapter
        checkBTState();

        btnOn.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                btnOn.setEnabled(false);
                mConnectedThread.write("1");    // Send "1" via Bluetooth
                //Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
            }
        });

        btnOff.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                btnOff.setEnabled(false);  
                mConnectedThread.write("0");    // Send "0" via Bluetooth
                //Toast.makeText(getBaseContext(), "Turn off LED", Toast.LENGTH_SHORT).show();
            }
        });
    }

    private BluetoothSocket createBluetoothSocket(BluetoothDevice device) throws IOException {
        if(Build.VERSION.SDK_INT >= 10){
            try {
                final Method  m = device.getClass().getMethod("createInsecureRfcommSocketToServiceRecord", new Class[] { UUID.class });
                return (BluetoothSocket) m.invoke(device, MY_UUID);
            } catch (Exception e) {
                Log.e(TAG, "Could not create Insecure RFComm Connection",e);
            }
        }
        return  device.createRfcommSocketToServiceRecord(MY_UUID);
    }

    @Override
    public void onResume() {
        super.onResume();

        Log.d(TAG, "...onResume - try connect...");

        // Set up a pointer to the remote node using it's address.
        BluetoothDevice device = btAdapter.getRemoteDevice(address);

        // Two things are needed to make a connection:
        //   A MAC address, which we got above.
        //   A Service ID or UUID.  In this case we are using the
        //     UUID for SPP.

        try {
            btSocket = createBluetoothSocket(device);
        } catch (IOException e) {
            errorExit("Fatal Error", "In onResume() and socket create failed: " + e.getMessage() + ".");
        }

        /*try {
      btSocket = device.createRfcommSocketToServiceRecord(MY_UUID);
    } catch (IOException e) {
      errorExit("Fatal Error", "In onResume() and socket create failed: " + e.getMessage() + ".");
    }*/

        // Discovery is resource intensive.  Make sure it isn't going on
        // when you attempt to connect and pass your message.
        btAdapter.cancelDiscovery();

        // Establish the connection.  This will block until it connects.
        Log.d(TAG, "...Connecting...");
        try {
            btSocket.connect();
            Log.d(TAG, "....Connection ok...");
        } catch (IOException e) {
            try {
                btSocket.close();
                Log.d(TAG, "Failing connect 1 "+e.getMessage());
            } catch (IOException e2) {
                Log.d(TAG, "Failing connect 2");
                errorExit("Fatal Error", "In onResume() and unable to close socket during connection failure" + e2.getMessage() + ".");
            }
        }

        // Create a data stream so we can talk to server.
        Log.d(TAG, "...Create Socket...");

        mConnectedThread = new ConnectedThread(btSocket);
        mConnectedThread.start();
    }

    @Override
    public void onPause() {
        super.onPause();

        Log.d(TAG, "...In onPause()...");

        //try     {
            //btSocket.close();
            mConnectedThread.cancel();
        //} catch (IOException e2) {
        //  errorExit("Fatal Error", "In onPause() and failed to close socket." + e2.getMessage() + ".");
        //}
    }

    private void checkBTState() {
        // Check for Bluetooth support and then check to make sure it is turned on
        // Emulator doesn't support Bluetooth and will return null
        if(btAdapter==null) { 
            errorExit("Fatal Error", "Bluetooth not support");
        } else {
            if (btAdapter.isEnabled()) {
                Log.d(TAG, "...Bluetooth ON...");
            } else {
                //Prompt user to turn on Bluetooth
                Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                startActivityForResult(enableBtIntent, 1);
            }
        }
    }

    private void errorExit(String title, String message){
        Toast.makeText(getBaseContext(), title + " - " + message, Toast.LENGTH_LONG).show();
        finish();
    }

    private class ConnectedThread extends Thread {
        private final InputStream mmInStream;
        private final OutputStream mmOutStream;
        private final BluetoothSocket mmSocket;


        public ConnectedThread(BluetoothSocket socket) {
            InputStream tmpIn = null;
            OutputStream tmpOut = null;
            BluetoothSocket tmpSck=null;
            // Get the input and output streams, using temp objects because
            // member streams are final
            try {
                tmpIn = socket.getInputStream();
                tmpOut = socket.getOutputStream();
                tmpSck=socket;
            } catch (IOException e) { }

            mmInStream = tmpIn;
            mmOutStream = tmpOut;
            mmSocket=tmpSck;
        }

        public void run() {
            android.os.Debug.waitForDebugger();
            byte[] buffer = new byte[256];  // buffer store for the stream
            int bytes; // bytes returned from read()

            // Keep listening to the InputStream until an exception occurs
            while (true) {
                try {
                    // Read from the InputStream
                    bytes = mmInStream.read(buffer);        // Get number of bytes and message in "buffer"
                    h.obtainMessage(RECIEVE_MESSAGE, bytes, -1, buffer).sendToTarget();     // Send to message queue Handler
                } catch (IOException e) {
                    break;
                } catch (NullPointerException npe) {
                    Log.d(TAG,npe.getMessage());
                }
            }
        }

        /* Call this from the main activity to send data to the remote device */
        public void write(String message) {
            Log.d(TAG, "...Data to send: " + message + "...");
            byte[] msgBuffer = message.getBytes();
            try {
                mmOutStream.write(msgBuffer);
            } catch (IOException e) {
                Log.d(TAG, "...Error data send: " + e.getMessage() + "...");     
            }
        }

        public void cancel() {
            try {
                mmSocket.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

I've read somewhere that Android after ICS has some issue with bluetooth tied to the OS itself.... I really hope this is not the case... Your help is greatly appreciated.

Answer 1

Kindly ensure pairing the device explicitly from your Android phone’s settings. Usually the pair code is 1234. The Hardware Tx,Rx pin are preferred if free on the Arduino. 96200 baud rate is generally better

Answer 2

Android 4.2 has a completely redesigned Bluetooth stack (Bluedroid), while earlier versions used Bluez. In 4.2 Bluedroid is known to have issues connecting to RFCOMM (also known as SPP). See here: https://code.google.com/p/android/issues/detail?id=41110

Android 4.3 supposedly fixes it. You can try upgrading to 4.3 with a firmware image from https://developers.google.com/android/nexus/images and see if that fixes the issue.