Wait to receive data without blocking ui thread bluetooth android

Question

I'm new to programming on android and I'm writing a simple application of a turn-based game that uses bluetooth. My app consists of Main Activity is responsible for starting a bluetooth connection and exchanging some configuration messages and a SecondActivity that implements a custom view with the game map. I can correctly pair the devices and exchange information between the two even in the custom view, the problem is that in the custom view I would wait to receive information without blocking the ui thread, at the moment I am waiting to receive data in this way

Custom view

state = bluetoothService.getState();
while(state != NOT_EMPTY){
    try {
        Thread.sleep(500);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    state = bluetoothService.getState();
}
info = bluetoothService.getMessage();

this obviously causes black screens and non-responsiveness, is there another way to wait to receive data?

The connection is managed through a BluetoothService class, with threads, the one that takes care of reading the data does this

private class ConnectedThread extends Thread {
        private final BluetoothSocket mSocket;
        private final InputStream mInStream;
        private final OutputStream mOutStream;

        public ConnectedThread(BluetoothSocket socket) {
            mSocket = socket;
            InputStream tmpIn = null;
            OutputStream tmpOut = null;

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

            mInStream = tmpIn;
            mOutStream = tmpOut;
        }

        public void run(){
            byte[] buffer = new byte[1024]; 

            int bytes; // bytes returned from read()

            // Keep listening to the InputStream until an exception occurs
            while (true) {
                // Read from the InputStream
                try {
                    bytes = mInStream.read(buffer);
                    if(bytes != 0) {
                        String incomingMessage = new String(buffer, 0, bytes);
                        message = incomingMessage;
                        mState = NOT_EMPTY;
                    }
                } catch (IOException e) {
                    break;
                }
            }
        }
}

//getMessage method just returns message if not null

Answer 1

The main idea is not to pull from the activity, but instead call a method of the activity from the background thread.

So when constructring your reader thread, pass a reference to the activity and create a handler:

    private SecondActivity mActivity;
    private Handler mActivityHandler;

    public ConnectedThread(BluetoothSocket socket, SecondActivity activity) {
        mActivity = activity;
        mActivityHandler = new Handler(activity.getMainLooper());

        ...
    }

When a message is received, call a method of the activity. The call must be done on the main thread, so use the handler:

final String message = incomingMessage;
Runnable runnable = new Runnable() {
    @Override 
    public void run() {
        mActivity.onMessageReceived(message);
    } 
};
mActivityHandler.post(myRunnable);

In the activity, do something with message:

public void onMessageReceived(String message) {
    // handle the message...
}