Disconnect a bluetooth socket in Android

Question

Hi,

I'm developing a program in which, from an Android Phone, I have to connect as a client to a Bluetooth medical sensor. I'm using the official Bluetooth API and no problem during connection (SPP profile), but when I end the socket, the sensor is still connected to my phone (although I have close the connection).

Are there any way to make a Bluetooth disconnection? I think there is an intent called ACTION_ACL_CONNECTED, which does that. Can anyone explain me how to use this?

Thanks in advance.

EDITED: Here is the code, if anyone needs additional info, it's a Nonin 4100 medical sensor.

Set<BluetoothDevice> pairedDevices = Activa.myBluetoothAdapter.getBondedDevices();
        // If there are paired devices
        if (pairedDevices.size() > 0) {
            // Loop through paired devices
            for (BluetoothDevice device : pairedDevices) {
                // Add the name and address to an array adapter to show in a ListView
                String name = device.getName();
                if (name.contains("Nonin")) {
                    try {
                        found = true;
//                      socket = device.createRfcommSocketToServiceRecord(UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));
//                      handler.sendEmptyMessage(5);
//                      Activa.myBluetoothAdapter.cancelDiscovery();
//                      socket.connect();
                        BluetoothDevice hxm = BluetoothAdapter.getDefaultAdapter().getRemoteDevice(device.getAddress());
                        Method m;
                        try {
                            m = hxm.getClass().getMethod("createRfcommSocket", new Class[]{int.class});
                            socket = (BluetoothSocket)m.invoke(hxm, Integer.valueOf(1));
                            handler.sendEmptyMessage(5);
                            socket.connect();
                        } catch (Exception e) {
                            handler.sendEmptyMessage(7);
                            e.printStackTrace();
                            break;
                        }
                        handler.sendEmptyMessage(6);
                        InputStream in = socket.getInputStream();
                        OutputStream out = socket.getOutputStream();
                        byte[] retrieve = { 0x44, 0x31};
                        out.write(retrieve);
                        byte [] ack = new byte [1];
                        in.read(ack);
                        if (ack[0] == 0x15) {
                            cancelMeasurement();
                            return;
                        }
                        byte [] data = new byte [3];
                        long timeStart = System.currentTimeMillis();
                        this.timePassed = System.currentTimeMillis() - timeStart;
                        while ((this.timePassed < (this.time))&&(this.finished)) {
                            try {
                                in.read(data);
                                processData(data);
                                Thread.sleep(1000);
                                this.timePassed = System.currentTimeMillis() - timeStart;
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                        in.close();
                        out.close();
                        socket.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
}

Answer 1

Please remember to close your Input/output streams first, then close the socket.

By closing the streams, you kick off the disconnect process. After you close the socket, the connection should be fully broken down.

If you close the socket before the streams, you may be bypassing certain shutdown steps, such as the (proper) closing of the physical layer connection.

Here's the method I use when its time to breakdown the connection.

/**
 * Reset input and output streams and make sure socket is closed. 
 * This method will be used during shutdown() to ensure that the connection is properly closed during a shutdown.  
 * @return
 */
private void resetConnection() {
        if (mBTInputStream != null) {
                try {mBTInputStream.close();} catch (Exception e) {}
                mBTInputStream = null;
        }

        if (mBTOutputStream != null) {
                try {mBTOutputStream.close();} catch (Exception e) {}
                mBTOutputStream = null;
        }

        if (mBTSocket != null) {
                try {mBTSocket.close();} catch (Exception e) {}
                mBTSocket = null;
        }

}

EDIT: Adding code for connect():

// bluetooth adapter which provides access to bluetooth functionality. 
BluetoothAdapter        mBTAdapter      = null;
// socket represents the open connection.
BluetoothSocket         mBTSocket   = null;
// device represents the peer
BluetoothDevice         mBTDevice       = null; 

// streams
InputStream           mBTInputStream  = null;
OutputStream          mBTOutputStream = null;

static final UUID UUID_RFCOMM_GENERIC = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");

/**
 * Try to establish a connection with the peer. 
 * This method runs synchronously and blocks for one or more seconds while it does its thing 
 * SO CALL IT FROM A NON-UI THREAD!
 * @return - returns true if the connection has been established and is ready for use. False otherwise. 
 */
private  boolean connect() {

        // Reset all streams and socket.
        resetConnection();

        // make sure peer is defined as a valid device based on their MAC. If not then do it. 
        if (mBTDevice == null) 
                mBTDevice = mBTAdapter.getRemoteDevice(mPeerMAC);

        // Make an RFCOMM binding. 
        try {mBTSocket = mBTDevice.createRfcommSocketToServiceRecord(UUID_RFCOMM_GENERIC);
        } catch (Exception e1) {
                msg ("connect(): Failed to bind to RFCOMM by UUID. msg=" + e1.getMessage());
                return false;
        }

        msg ("connect(): Trying to connect.");

        try {
                mBTSocket.connect();
        } catch (Exception e) {
                msg ("connect(): Exception thrown during connect: " + e.getMessage());
                return false;
        }

        msg ("connect(): CONNECTED!");

        try {
                mBTOutputStream = mBTSocket.getOutputStream();
                mBTInputStream  = mBTSocket.getInputStream();
        } catch (Exception e) {
                msg ("connect(): Error attaching i/o streams to socket. msg=" + e.getMessage());
                return false;
        }

        return true;
}

Answer 2

HI,

I've seen the exact same problem (HTC Desire). Despite closing the socket by the book (as Brad suggests), the next connect() blocks forever - until ended by close() by another thread.

I circumvented the problem by always calling BluetoothAdapter.disable()/.enable() before connecting. Awful, unfriendly hack, I know...

I suspect that some of the present BT issues are manufacturer specific, as some app implementors seem to live happily with createRfcommSocketToServiceRecord(), which definitely fails on my HTC Desire (Android 2.1 update 1).

I have seen indications (sorry, don't have references) that HTC Desire's BT stack differs from the Nexus One, although they seem to be very similar devices...

BR Per

(addition) Here's a very simple activity to reproduce the problem (without my disable/enable 'cure'):

package com.care2wear.BtTest;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class BtTestActivity extends Activity {
    private static final String TAG="BtTest";

    BluetoothAdapter mBtAdapter = null;
    BluetoothDevice mBtDev = null;
    BluetoothSocket mBtSocket = null;
    InputStream isBt;
    OutputStream osBt;  
    String mAddress = "00:18:E4:1C:A4:66";

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


        init();

        connect();  // ok
        disconnect(); // ok
        connect(); // this invariably fails - blocked until BT is switched off by someone else, or the peer device turns off/goes out of range
        disconnect();
    }

    private void init() {
        Log.d(TAG, "initializing");
        mBtAdapter = BluetoothAdapter.getDefaultAdapter();
        mBtDev = mBtAdapter.getRemoteDevice(mAddress);
        Log.d(TAG, "initialized");
    }

    private void connect() {
        try {
            Log.d(TAG, "connecting");
            Method m = mBtDev.getClass().getMethod("createRfcommSocket", new Class[] { int.class });
            mBtSocket = (BluetoothSocket) m.invoke(mBtDev, 1);
            mBtSocket.connect();
            Log.d(TAG, "connected");
        } catch (SecurityException e) {
            Log.e(TAG, "SecEx", e);
        } catch (NoSuchMethodException e) {
            Log.e(TAG, "NsmEx", e);
        } catch (IllegalArgumentException e) {
            Log.e(TAG, "IArgEx", e);
        } catch (IllegalAccessException e) {
            Log.e(TAG, "IAccEx", e);
        } catch (InvocationTargetException e) {
            Log.e(TAG, "ItEx", e);
        } catch (IOException e) {
            Log.e(TAG, "IOEx", e);
        }

    }

    private void disconnect() {
        Log.d(TAG, "closing");

        if (isBt != null) {
            try {
                isBt.close();
            } catch (IOException e) {
                Log.e(TAG, "isBt IOE", e);              
            }
            isBt = null;
        }
        if (osBt != null) {
            try {
                osBt.close();
            } catch (IOException e) {
                Log.e(TAG, "osBt IOE", e);              
            }
            osBt = null;
        }
        if (mBtSocket != null) {
            try {
                mBtSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "socket IOE", e);                
            }
            mBtSocket = null;
        }
        Log.d(TAG, "closed");       
    }
}

If anyone can spot if I'm doing it wrongly, feel free to comment :)

(addition 2) I think I got it to work now:

1. The official method of connecting RFCOMM (via SDP) now actually seems to work (HTC Desire, 2.1 update 1), BUT I had to remove and re-pair the BT device. Go figure..
2. Reconnection may still fail (service discovery failure) if I reconnect 'too quickly' (quit app, then immediately restart). Guess the connection is not completely down yet..
3. If I always end the (last) activity not only with finish(), but also with Runtime.getRuntime().exit(0);, it works a lot better. Go figure again...

If anyone can explain this, I'll happily learn. /Per

(addition 3) Finally got the Froyo (2.2) update for my Desire, and as far as I can see, SPP now works :) /Per

Answer 3

Hi,

I was developing an app that conects to a BT device. Your code works fine in my HTC Wildfire but with a Samsung Galaxy I5700 doen't work. Both os are 2.1 update but.....

The exception was 'InvocationTargetException'

The only thing I had to modify is the disconnect().

private void disconnect() { if(Conectado){ try { mBtSocket.close(); texto.setText(texto.getText()+"\nDesconectado"); Conectado = false; } catch (IOException e1) { // TODO Auto-generated catch block texto.setText(texto.getText()+"\n"+e1.getMessage()); } catch (Exception e2) { // TODO Auto-generated catch block texto.setText(texto.getText()+"\n"+e2.getMessage()); }
}