Bluetooth data transfer between two Android devices

Question

I have been following this Android guide for Bluetooth communication

To explain exactly what I want to do, when the two devices are paired, two different activities open up on each device (server and client) where on the server activity I have different buttons, and on the client activity there is just a textview. I want to be able to press a button on the server device and display it on the client.

I have managed to establish a connection between the two devices, but now I want to send data which I have not been able to do.

They give this code for data transfer:

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() {
    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
            mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
                    .sendToTarget();
        } catch (IOException e) {
            break;
        }
    }
}

/* Call this from the main activity to send data to the remote device */
public void write(byte[] bytes) {
    try {
        mmOutStream.write(bytes);
    } catch (IOException e) { }
}

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

But this line generates an error

// Send the obtained bytes to the UI activity
            mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer).sendToTarget();

And is not explained in the guide. I don't know what the mHandler is or does.

Apart from the error, I don't even really understand where to put this code. Should it be in the second activities (server and client) that I open or in the main? If in the Server activity, should it be in the onClick method for all the buttons with a different byte code to send for each button? And in this code, how do we distinguish who is sending and who is receiving?

Answer 1

Check out the BluetoothChat example that Google provides in the SDK. It'll show you how to implement basic sending of text over bluetooth.