Question

I need to connect my android to a bluetooth device. I use the BluetoothChat sample from Google.

I had some trouble to do this with a Google Nexus one, because the Nexus was making the connection but disconnects right after. I need to initiate twice time the connection as workaround (see connectionLost()).

Now, it works well on the Nexus One and on the HTC Desire too.

My problem is the disconnection at application exit. It works fine on the Nexus one, the connection is closed, but not on the HTC Desire. I add the inputstream/outputstream close function in addition to the socket close. Have a look at the “stop()” function.

package xxx.yyy.zzz;

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

import activities.Act_Main;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Context;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;

/**
 * This class does all the work for setting up and managing Bluetooth
 * connections with other devices. It has a thread that listens for
 * incoming connections, a thread for connecting with a device, and a
 * thread for performing data transmissions when connected.
 */
public class BluetoothService {
    // Debugging
    private static final String TAG = "BluetoothService";
    private static final boolean D = true;

    // Member fields
    //private final BluetoothAdapter mAdapter;
    private final Handler mHandler;
    private ConnectThread mConnectThread;
    private ConnectedThread mConnectedThread;
    private int mState;
    private String mBTAddress;
    private boolean isStop = false;

    // Constants that indicate the current connection state
    public static final int STATE_NONE = 0;       // we're doing nothing
    public static final int STATE_LISTEN = 1;     // now listening for incoming connections
    public static final int STATE_CONNECTING = 2; // now initiating an outgoing connection
    public static final int STATE_CONNECTED = 3;  // now connected to a remote device

    /**
     * Constructor. Prepares a new Act_Main session.
     * @param context  The UI Activity Context
     * @param handler  A Handler to send messages back to the UI Activity
     */
    public BluetoothService(Context context, Handler handler)
    {
        //mAdapter = BluetoothAdapter.getDefaultAdapter();
        mState = STATE_NONE;
        mHandler = handler;
    }

    /**
     * Set the current state of the connection
     * @param state  An integer defining the current connection state
     */
    private synchronized void setState(int state)
    {
        if (D) Log.d(TAG, "setState() " + mState + " -> " + state);
        mState = state;

        // Give the new state to the Handler so the UI Activity can update
        mHandler.obtainMessage(Act_Main.MESSAGE_STATE_CHANGE, state, -1).sendToTarget();
    }

    /**
     * Return the current connection state. */
    public synchronized int getState()
    {
        return mState;
    }

    /**
     * Start the ConnectThread to initiate a connection to a remote device.
     * @param device  The BluetoothDevice to connect
     */
    public synchronized void connect(String BTAddress)
    {
        mBTAddress = BTAddress ;

        // Get the BLuetoothDevice object
        BluetoothDevice device = BluetoothAdapter.getDefaultAdapter().getRemoteDevice(BTAddress);

        if (D) Log.d(TAG, "connect to: " + device);

        // Cancel any thread attempting to make a connection
        if (mState == STATE_CONNECTING)
            if (mConnectThread != null) {mConnectThread.cancel(); mConnectThread = null;}

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

        // Start the thread to connect with the given device
        mConnectThread = new ConnectThread(device);
        mConnectThread.start();
        setState(STATE_CONNECTING);
        isStop = false ;
    }

    /**
     * Start the ConnectedThread to begin managing a Bluetooth connection
     * @param socket  The BluetoothSocket on which the connection was made
     * @param device  The BluetoothDevice that has been connected
     */
    public synchronized void connected(BluetoothSocket socket, BluetoothDevice device)
    {
        if (D) Log.d(TAG, "connected");

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

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

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

        // Send the name of the connected device back to the UI Activity
        Message msg = mHandler.obtainMessage(Act_Main.MESSAGE_DEVICE_NAME);
        Bundle bundle = new Bundle();
        bundle.putString(Act_Main.DEVICE_NAME, device.getName());
        msg.setData(bundle);
        mHandler.sendMessage(msg);

        setState(STATE_CONNECTED);
    }

    /**
     * Stop all threads
     */
    public synchronized void stop()
    {
        isStop = true ;

        if (D)
            Log.d(TAG, "stop");

        if(mConnectThread != null)
        {
            mConnectThread.cancel();
            Thread moribund = mConnectThread;
            mConnectThread = null;
            moribund.interrupt();
        }

        if(mConnectedThread != null)
        {
            mConnectedThread.cancel();
            Thread moribund = mConnectedThread;
            mConnectedThread = null;
            moribund.interrupt();
        }

        setState(STATE_NONE);
    }

    /**
     * Write to the ConnectedThread in an unsynchronized manner
     * @param out The bytes to write
     * @see ConnectedThread#write(byte[])
     */
    public void write(byte[] out)
    {
        // Create temporary object
        ConnectedThread r;

        // Synchronize a copy of the ConnectedThread
        synchronized (this)
        {
            Log.d(TAG, "BT_SEND_MESSAGE");

            if (mState != STATE_CONNECTED)
                return;

            r = mConnectedThread;
        }

        // Perform the write unsynchronized
        r.write(out);
    }

    /**
     * Indicate that the connection attempt failed and notify the UI Activity.
     */
    private void connectionFailed()
    {
        try
        {
            synchronized (this)
            {
                this.wait(3000);
            }
            connect(mBTAddress);
        }
        catch(InterruptedException ex)
        {
            Log.e(TAG, "WAIT_EXCEPTION:"+ ex.getMessage());
        }
    }

    /**
     * Indicate that the connection was lost and notify the UI Activity.
     */
    private void connectionLost()
    {
        if (!isStop)
            connect(mBTAddress);
    }

    /**
     * This thread runs while attempting to make an outgoing connection
     * with a device. It runs straight through; the connection either
     * succeeds or fails.
     */
    private class ConnectThread extends Thread
    {
        private final BluetoothSocket mmSocket;
        private final BluetoothDevice mmDevice;

        public ConnectThread(BluetoothDevice device)
        {
            mmDevice = device;
            BluetoothSocket tmp = null;

            // Get a BluetoothSocket for a connection with the
            // given BluetoothDevice
            try
            {
                tmp = device.createRfcommSocketToServiceRecord(UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));
            }
            catch (Exception e)
            {
                Log.e(TAG, "create() failed", e);
            }
            mmSocket = tmp;
        }

        public void run()
        {
            Log.i(TAG, "BEGIN mConnectThread");
            setName("ConnectThread");

            // Always cancel discovery because it will slow down a connection
            //mAdapter.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(TAG, "unable to close() socket during connection failure", e2);
                }
                return;
            }

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

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

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

    /**
     * This thread runs during a connection with a remote device.
     * It handles all incoming and outgoing transmissions.
     */
    private class ConnectedThread extends Thread {
        private BluetoothSocket mmSocket;
        private InputStream mmInStream;
        private OutputStream mmOutStream;

        public ConnectedThread(BluetoothSocket socket) {
            Log.d(TAG, "create ConnectedThread");
            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(TAG, "temp sockets not created", e);
            }

            mmInStream = tmpIn;
            mmOutStream = tmpOut;
        }

        public void run()
        {
            Log.i(TAG, "BEGIN mConnectedThread");
            byte[] buffer;
            int bytes = 0;

            // Keep listening to the InputStream while connected
            while (true)
            {
                try
                {
                    //Clear buffer
                    buffer = new byte[1024];

                    // Read from the InputStream
                    bytes = mmInStream.read(buffer);

                    // Send the obtained bytes to the UI Activity
                    mHandler.obtainMessage(Act_Main.MESSAGE_READ, bytes, -1, buffer).sendToTarget();
                }
                catch (IOException e)
                {
                    //String bufferStr = new String(buffer, 0, buffer.length);
                    Log.e(TAG, "disconnected", e);
                    connectionLost();
                    break;
                }
            }
        }

        /**
         * Write to the connected OutStream.
         * @param buffer  The bytes to write
         */
        public void write(byte[] buffer)
        {
            try
            {
                mmOutStream.write(buffer);
            }
            catch (IOException e)
            {
                Log.e(TAG, "Exception during write", e);
            }
        }

        public void cancel()
        {
            if (mmOutStream != null)
            {
                try {mmOutStream.close();} catch (Exception e) { Log.e(TAG, "close() of outputstream failed", e); }
                mmOutStream = null;
            }

            if (mmInStream != null)
            {
                try {mmInStream.close();} catch (Exception e) { Log.e(TAG, "close() of inputstream failed", e); }
                mmInStream = null;
            }

            if (mmSocket != null)
            {
                try {mmSocket.close();} catch (Exception e) { Log.e(TAG, "close() of connect socket failed", e); }
                mmSocket = null;
            }
        }
    }
}

Thanks in advance for your help.

JJ

Answer 1

Quick comment about synchronization in your code:

Leave the synchronized keyword on your connect() method, but when it comes time to connect, call your connect() from a thread, rather than creating a thread from your connect(). As it stands now, your code is firing off a connect thread from connect() and defeating the purpose of synchronization. (The purpose being to synchronize requests to connect() so that multiple threads don’t get jumbled up as they try to connect at the same time). This may well be causing some of your connection issues.

regarding the HTC:

I think you and I encountered the same issue: Why can't HTC Droid running OTA 2.1 communicate with RFCOMM?

A note about disconnecting a bluetooth connection:

Make sure to disconnect gracefully every time using your cancel() method.