Where/how to place drawing functions when listening bluetooth

Question

I'm successfully receiving data from microcontroller using bluetoth serial protocol as described, for example, in this tutorial:

http://solderer.tv/data-transfer-between-android-and-arduino-via-bluetooth/

I'am able to display the values I receive in a textView, but as soon as I try to graphically display the values, by adding a line whose length depends on the value, the application crashes.

I think I'm ok with the drawing functions themselves because I'm able to draw static pictures when the app starts:

Bitmap bg = Bitmap.createBitmap(480, 800, Bitmap.Config.ARGB_8888);
canvas = new Canvas(bg);
Paint paint = new Paint();
paint.setColor(Color.parseColor(#6b8728));
paint.setXfermode(null);
canvas.drawLine(x, y, x2, y2, paint);

Bt maybe at the end should i use another way.

Anyway, this introduced, here's my problem. When I implement those drawing functions in the data listening thread, the app crashes. Hence I do not know how to perform the line drawing: new thread needed?( and how to do that?), painting has to be done in specific parts? Specific functions to use?...

I hope my question is clear, otherwise I'll be happy to add more details.

Thank you in advance for your help.

Kind regards,

Sylvain

Edit:

Adding my function:

 void beginListenForData()
    {


        final Handler handler = new Handler();
        final byte delimiter = 10; //This is the ASCII code for a newline character

        stopWorker = false;
        readBufferPosition = 0;
        readBuffer = new byte[1024];
        workerThread = new Thread(new Runnable()
        {
            public void run()
            {
                final TextView t = (TextView)findViewById(R.id.textView);
                while(!Thread.currentThread().isInterrupted() && !stopWorker)
                {

                    try
                    {
                        int bytesAvailable = mmInputStream.available();
                        if(bytesAvailable > 0)
                        {
                            byte[] packetBytes = new byte[bytesAvailable];
                            mmInputStream.read(packetBytes);
                            for(int i=0;i<bytesAvailable;i++)
                            {
                                byte b = packetBytes[i];
                                if(b == delimiter)
                                {
                                    byte[] encodedBytes = new byte[readBufferPosition];
                                    System.arraycopy(readBuffer, 0, encodedBytes, 0, encodedBytes.length);
                                    final String data = new String(encodedBytes, "US-ASCII");
                                    readBufferPosition = 0;

                                    Toast.makeText(MainActivity.this, data,
                                            Toast.LENGTH_SHORT).show();
                                    handler.post(new Runnable()
                                    {
                                        public void run() {

                                            t.setText(data);
                                            String[] separated = data.split(":");
                                            separated[1].trim();

                                            if ((separated[0].length() != 0)&& (separated[1].length() != 0)) {
                                            t.append("\n" + separated[0]);
                                            t.append("\n" + separated[1]);

                                            t.append("\ntest");
                                            String s_angle = separated[0];
                                            String s_value = separated[1];

                                            final Integer angle = Integer.parseInt(s_angle);
                                            final Integer value = Integer.parseInt(s_value)/1000;
                                                // Crashing here
                                                Paint paint = new Paint();
                                                paint.setColor(Color.parseColor("#6b8728"));

                                                int width = canvas.getWidth()/2;
                                                int height = canvas.getHeight()/2;

                                                canvas.drawLine(width,height,150,50, paint);



                                         }





                                        }
                                    });
                                }
                                else
                                {
                                    readBuffer[readBufferPosition++] = b;
                                }
                            }
                        }
                        else
                        {
                            //t.append(bytesAvailable+"\n");
                        }
                    }
                    catch (IOException ex)
                    {
                        stopWorker = true;
                    }
                }
            }
        });

        workerThread.start();
    }

Answer 1

All UI related activities must be done in UI/Main thread. One of way of doing it:

new Handler(Looper.getMainLooper()).post(new Runnable() {
    @Override
    public void run() {
        //your UI code goes here
    }
});

Answer 2

I've used runOnUiThread:

runOnUiThread(new Runnable() {
                                                    @Override
                                                    public void run() {
                                                        Paint paint = new Paint();
                                                        paint.setColor(Color.parseColor("#6b8728"));
                                                        //Bitmap bg = Bitmap.createBitmap(480, 800, Bitmap.Config.ARGB_8888);
                                                        //Canvas canvas = new Canvas(bg);
                                                        int width = canvas.getWidth() / 2;
                                                        int height = canvas.getHeight() / 2;

                                                        canvas.drawLine(width, height, 150, 50, paint);          
                                                    }
                                                });