bluetoothActivity

  private static final String DEVICE_ADDRESS = "XX:XX:XX:XX:XX:XX";
    private static final UUID MY_UUID = UUID.randomUUID();

    private BluetoothAdapter bluetoothAdapter;
    private BluetoothSocket bluetoothSocket;

    private InputStream inputStream;

    private GraphView temperatureGraph;
    private LineGraphSeries<DataPoint> series;

    private double graphLastXValue = 0d;
    private static final int MESSAGE_READ = 1;

    private Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(@NonNull Message msg) {
            if (msg.what == MESSAGE_READ) {
                String readMessage = (String) msg.obj;
                double temperature = Double.parseDouble(readMessage);
                addEntry(temperature);
            }
            return true;

        }
    });

    private void addEntry(double temperature) {
        graphLastXValue += 1d;
        series.appendData(new DataPoint(graphLastXValue, temperature), true, 100);

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        try {
            bluetoothSocket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }