how to connect and send a message to multiple devices through blue tooth in android?

Question

I would like to develop an application for sending a message to multiple devices through blue tooth.I know blue tooth is a point to point communication even though i would like to connect and send a message as following steps:

1.Get the list of paired devices

2.Select a device from paired list

3.Connect to paired device , send a message to selected paired device

4.Disconnect from device

5.Get connection to another device and so on (one after another).

I am getting paired devices addresses list as follows:

       mBtAdapter = BluetoothAdapter.getDefaultAdapter();

      Set<BluetoothDevice> pairedDevices = mBtAdapter.getBondedDevices();


    if (pairedDevices.size() > 0) {
     for (BluetoothDevice device : pairedDevices) {

        pairedList.add(device.getAddress());

        }

     Log.v("11111111", "11111111111"+dev);
    }

I am trying to connect to them and sending a message when user clicks on a button as follows:

      ((Button)findViewById(R.id.button1)).setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {


        String message = "Haiii";

        for(int i=0;i<dev.size();i++){
            Log.v("device", "111111  :  "+pairedList.get(i));
        mbService.connect(mBtAdapter.getRemoteDevice(pairedList.get(i)));

                    mbService.write(message.getBytes());

                    mbService.stop();
        }




    }
}); 

From the above code i am getting connection when loop pairedList.get(0).But the message is not sending to another device.In another device api sample application has installed.

If I use pairedList.get(i) it is not connecting to any devices even single device also.

please help me .

Answer 1

try to create separate threads for each connection - I had a similar issue and creating a new thread for each connection solved it nicely. By the way I even create a new thread to establish the connection - so establishing the connection does not block the UI. Got this from the BT sample code...

to create a new thread to establish a connection:

    mConnectBluetoothThread = new ConnectBluetoothThread(device);
    mConnectBluetoothThread.start();

where ConnectBluetoothThread is defined like:

public ConnectBluetoothThread(BluetoothDevice device) {
        if (DEBUG)
        Log.i(this.getClass().getSimpleName(),
            this.getClass().getName()
                + " ->"
                + Thread.currentThread().getStackTrace()[2]
                    .getMethodName());

        mmDevice = device;
        BluetoothSocket tmp = null;

        // Get a BluetoothSocket for a connection with the
        // given BluetoothDevice
        try {
        tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) {
        Log.e(this.getClass().getSimpleName(), "create() failed", e);
        }
        mmSocket = tmp;
    }

    public void run() {
        if (DEBUG)
        Log.i(this.getClass().getSimpleName(),
            this.getClass().getName()
                + " ->"
                + Thread.currentThread().getStackTrace()[2]
                    .getMethodName());
        // TODO
        setName("ConnectThread");

        // Always cancel discovery because it will slow down a connection
        mBluetoothAdapter.cancelDiscovery();

        // Make a connection to the BluetoothSocket
        try {
        // This is a blocking call and will only return on a
        // successful connection or an exception
        mmSocket.connect();
        } catch (IOException e) {

        connectionFailed();

        // Close the socket
        try {
            mmSocket.close();
        } catch (IOException e2) {
            Log.e(this.getClass().getSimpleName(),
                "unable to close() socket during connection failure",
                e2);
        }

        return;
        }

        // Reset the ConnectThread because we're done
        synchronized (InterBT.this) {
        mConnectBluetoothThread = null;
        }

        // Start the connected thread
        connected(mmSocket, mmDevice);
    }

    public void cancel() {
        try {
        mmSocket.close();
        } catch (IOException e) {
        Log.e(this.getClass().getSimpleName(),
            "close() of connect socket failed", e);
        }
    }
    }

    public synchronized void connected(BluetoothSocket socket,
        BluetoothDevice device) {
    if (DEBUG)
        Log.d(this.getClass().getSimpleName(), "connected");

    // Cancel the thread that completed the connection
    if (mConnectBluetoothThread != null) {
        mConnectBluetoothThread.cancel();
        mConnectBluetoothThread = null;
    }

    // Cancel any thread currently running a connection
    if (mConnectedBluetoothThread != null) {
        mConnectedBluetoothThread.cancel();
        mConnectedBluetoothThread = null;
    }

    // Cancel the accept thread because we only want to connect to one
    // device
    // if (mAcceptThread != null) {mAcceptThread.cancel(); mAcceptThread =
    // null;}

    // Start the thread to manage the connection and perform transmissions
    mConnectedBluetoothThread = new ConnectionThreadBT(socket);
    mConnectedBluetoothThread.start();

    setState(STATE_CONNECTED);

    }

and also create a new class ConnectionThreadBT that handles the connection to read and write:

public class ConnectionThreadBT extends ConnectionThreadBase {
    private static final boolean DEBUG = true;

    private final BluetoothSocket mmSocket;
    private final InputStream mmInStream;
    private final OutputStream mmOutStream;
    byte[] responseBuffer = new byte[4096 * 4]; 
    int responseBufferLen = 0;


    public ConnectionThreadBT(BluetoothSocket socket) {
    if (DEBUG)
        Log.i(this.getClass().getSimpleName(),
            this.getClass().getName()
                + " ->"
                + Thread.currentThread().getStackTrace()[2]
                    .getMethodName());

    mmSocket = socket;
    InputStream tmpIn = null;
    OutputStream tmpOut = null;

    // Get the BluetoothSocket input and output streams
    try {
        tmpIn = socket.getInputStream();
        tmpOut = socket.getOutputStream();
    } catch (IOException e) {
        Log.e(this.getClass().getSimpleName(), "temp sockets not created",
            e);
    }

    mmInStream = tmpIn;
    mmOutStream = tmpOut;
   }

    public void run() {
    if (DEBUG)
        Log.i(this.getClass().getSimpleName(),
            this.getClass().getName()
                + " ->"
                + Thread.currentThread().getStackTrace()[2]
                    .getMethodName());
    //we have successfully connected to BT

    //now inform UI 

    Home_Screen.sendMessageToHomeScreen(
        Home_Screen.MESSAGE_INTERBT_CONNECTION_TESTED,
        Home_Screen.CONNECTION_SUCCESS, true);
  }

and then to write just call this method which is also defined within ConnectionThreadBT

public void sendMsg(MyBuffer buffer){
        try {
        mmOutStream.write(buffer);
        mmOutStream.flush();
        successfullyWritten = true;
        } catch (IOException e) {
        Log.e(this.getClass().getSimpleName(),
            "Exception during write", e);
        successfullyWritten = false;
        }

to read either do the same or start a monitoring loop in the run method which keeps reading as long as the connectedThread is alive and reports back any read information through a handler similar to the UI screen update