Realicé la depuración de mi proyecto y mi 3. fragmento no puede conectar el servicio Bluetooth. Eso incluye enviar mensajes a otros dispositivos. Mi conexión está comenzando el primer fragmento. La identificación de mi dispositivo y el nombre del dispositivo deben mantener el servicio de Bluetooth, pero me conecto con el siguiente código, mi conexión es nula y el objeto nulo devuelto ConnectedThread. Entonces, ¿cómo puedo volver a conectar el servicio Bluetooth de Java en mi fragmento?

Llamo a esta línea en mi Fragmento

   mBluetoothConnection = new BluetoothConnectionService(getActivity().getApplicationContext());

Y la función de escritura en BluetoothService.java

button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                byte[] bytes = editText.getText().toString().getBytes(Charset.defaultCharset());

                mBluetoothConnection.write(bytes);

            }
        })

Mi punto de interrupción enmBluetoothConnection.write(bytes); esta línea y cada ConnectedThread, outputstream return null y ¿por qué?

Y este es mi servicio:

public class BluetoothConnectionService {
    private static final String TAG = "BluetoothConnectionServ";

    private static final String appName = "MYAPP";

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

    private final BluetoothAdapter mBluetoothAdapter;
    Context mContext;

    private AcceptThread mInsecureAcceptThread;

    private ConnectThread mConnectThread;
    private BluetoothDevice mmDevice;
    private UUID deviceUUID;
    ProgressDialog mProgressDialog;

    private ConnectedThread mConnectedThread;

    public BluetoothConnectionService(Context context) {
        mContext = context;
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        start();
    }




    /**
     * This thread runs while listening for incoming connections. It behaves
     * like a server-side client. It runs until a connection is accepted
     * (or until cancelled).
     */
    private class AcceptThread extends Thread {

        // The local server socket
        private final BluetoothServerSocket mmServerSocket;

        public AcceptThread(){
            BluetoothServerSocket tmp = null;

            // Create a new listening server socket
            try{
                tmp = mBluetoothAdapter.listenUsingInsecureRfcommWithServiceRecord(appName, MY_UUID_INSECURE);

                Log.d(TAG, "AcceptThread: Setting up Server using: " + MY_UUID_INSECURE);
            }catch (IOException e){
                Log.e(TAG, "AcceptThread: IOException: " + e.getMessage() );
            }

            mmServerSocket = tmp;
        }

        public void run(){
            Log.d(TAG, "run: AcceptThread Running.");

            BluetoothSocket socket = null;

            try{
                // This is a blocking call and will only return on a
                // successful connection or an exception
                Log.d(TAG, "run: RFCOM server socket start.....");
                if(socket == null)
                socket = mmServerSocket.accept();
                Log.d(TAG, "run: RFCOM server socket accepted connection.");

            }catch (IOException e){
                Log.e(TAG, "AcceptThread: IOException: " + e.getMessage() );
            }

            //talk about this is in the 3rd
            if(socket != null){
                Log.d(TAG, "run: Connected is active");

                connected(socket,mmDevice);
            }

            Log.i(TAG, "END mAcceptThread ");
        }

        public void cancel() {
            Log.d(TAG, "cancel: Canceling AcceptThread.");
            try {
                mmServerSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "cancel: Close of AcceptThread ServerSocket failed. " + e.getMessage() );
            }
        }

    }

    /**
     * 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 BluetoothSocket mmSocket;

        public ConnectThread(BluetoothDevice device, UUID uuid) {
            Log.d(TAG, "ConnectThread: started.");
            mmDevice = device;
            deviceUUID = uuid;
        }

        public void run(){
            BluetoothSocket tmp = null;
            Log.i(TAG, "RUN mConnectThread ");

            // Get a BluetoothSocket for a connection with the
            // given BluetoothDevice
            try {
                Log.d(TAG, "ConnectThread: Trying to create InsecureRfcommSocket using UUID: "
                        +MY_UUID_INSECURE );
                tmp = mmDevice.createRfcommSocketToServiceRecord(deviceUUID);
            } catch (IOException e) {
                Log.e(TAG, "ConnectThread: Could not create InsecureRfcommSocket " + e.getMessage());
            }

            mmSocket = tmp;

            // 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();

                Log.d(TAG, "run: ConnectThread connected.");
            } catch (IOException e) {
                // Close the socket
                try {
                    mmSocket.close();
                    Log.d(TAG, "run: Closed Socket.");
                } catch (IOException e1) {
                    Log.e(TAG, "mConnectThread: run: Unable to close connection in socket " + e1.getMessage());
                }
                Log.d(TAG, "run: ConnectThread: Could not connect to UUID: " + MY_UUID_INSECURE );
            }

            //will talk about this in the 3rd video

            connected(mmSocket,mmDevice);
        }
        public void cancel() {
            try {
                Log.d(TAG, "cancel: Closing Client Socket.");
                mmSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "cancel: close() of mmSocket in Connectthread failed. " + e.getMessage());
            }
        }
    }



    /**
     * Start the chat service. Specifically start AcceptThread to begin a
     * session in listening (server) mode. Called by the Activity onResume()
     */
    public synchronized void start() {
        Log.d(TAG, "start");

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

        if (mInsecureAcceptThread == null) {
            mInsecureAcceptThread = new AcceptThread();
            mInsecureAcceptThread.start();
        }
    }

    /**
     AcceptThread starts and sits waiting for a connection.
     Then ConnectThread starts and attempts to make a connection with the other devices AcceptThread.
     **/

    public void startClient(BluetoothDevice device,UUID uuid){
        Log.d(TAG, "startClient: Started.");

        //initprogress dialog
        mProgressDialog = ProgressDialog.show(mContext,"Connecting Bluetooth"
                ,"Please Wait...",true);

        mConnectThread = new ConnectThread(device, uuid);
        mConnectThread.start();
    }

    /**
     Finally the ConnectedThread which is responsible for maintaining the BTConnection, Sending the data, and
     receiving incoming data through input/output streams respectively.
     **/
    private class ConnectedThread extends Thread {
        private final BluetoothSocket mmSocket;
        private final InputStream mmInStream;
        private final OutputStream mmOutStream;

        public ConnectedThread(BluetoothSocket socket) {
            Log.d(TAG, "ConnectedThread: Starting.");

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

            //dismiss the progressdialog when connection is established
            try{
                mProgressDialog.dismiss();
            }catch (NullPointerException e){
                e.printStackTrace();
            }


            try {
                tmpIn = mmSocket.getInputStream();
                tmpOut = mmSocket.getOutputStream();
            } catch (IOException e) {
                e.printStackTrace();
            }

            mmInStream = tmpIn;
            mmOutStream = tmpOut;
        }

        public void run(){
            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) {
                // Read from the InputStream
                try {
                    bytes = mmInStream.read(buffer);
                    String incomingMessage = new String(buffer, 0, bytes);
                    Log.d(TAG, "InputStream: " + incomingMessage);
                    Intent incomingMessageIntent = new Intent("incomingMessage");

                    incomingMessageIntent.putExtra("theMessage", incomingMessage);
                    LocalBroadcastManager.getInstance(mContext).sendBroadcast(incomingMessageIntent);

                } catch (IOException e) {
                    Log.e(TAG, "write: Error reading Input Stream. " + e.getMessage() );
                    break;
                }
            }
        }







        //Call this from the main activity to send data to the remote device
        public void write(byte[] bytes) {
            String text = new String(bytes, Charset.defaultCharset());
            Log.d(TAG, "write: Writing to outputstream: " + text);
            try {
                mmOutStream.write(bytes);
            } catch (IOException e) {
                Log.e(TAG, "write: Error writing to output stream. " + e.getMessage() );
            }
        }

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

    private void connected(BluetoothSocket mmSocket, BluetoothDevice mmDevice) {
        Log.d(TAG, "connected: Starting.");

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

    /**
     * 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;
        if(mConnectedThread==null){
return;
        }
        // Synchronize a copy of the ConnectedThread
        Log.d(TAG, "write: Write Called.");
        //perform the write
        mConnectedThread.write(out);
    }

}

;