public class MainActivity extends Activity {
LinearLayout pianoKeysContainer;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);

     pianoKeysContainer = (LinearLayout) findViewById(R.id.key_container);
    pianoKeysContainer.setOnTouchListener(onYourViewTouchListener);

}


//Here we load the view positions after render it and fill the array with the positions
private List<Integer> positionsLeft_whiteKeys  = new ArrayList<Integer>();
private List<Integer> positionsRight_whiteKeys = new ArrayList<Integer>();

public void onWindowFocusChanged(boolean hasFocus)
{
    super.onWindowFocusChanged(hasFocus);

    for (int i = 0; i < pianoKeysContainer.getChildCount(); i++)
    {
        //positionsLeft_whiteKeys holds the start x of each view.
        positionsLeft_whiteKeys.add(pianoKeysContainer.getChildAt(i).getLeft());
        //positionsRight_whiteKeys holds the end x of each view.
        positionsRight_whiteKeys.add(pianoKeysContainer.getChildAt(i).getRight());
    }
}

public View.OnTouchListener onYourViewTouchListener = new View.OnTouchListener()
{
    float positionX;
    FrameLayout pianoKey;
    FrameLayout lastPlayedKey;
    ArrayList<FrameLayout> pressedKeys = new ArrayList<FrameLayout>();

    @Override
    public boolean onTouch(View view, MotionEvent motionEvent)
    {

        positionX = motionEvent.getX();

        float pitch;

        //Looping on the child of the layout which contains the piano keys
        for (int x = 0; x < ((LinearLayout) view).getChildCount(); x++)
        {
            // Calculating the pitch to get good chords
            pitch = (float) Math.pow(Math.pow(2.0, 1 / 12.0), (float) x);

            pianoKey = (FrameLayout) ((LinearLayout) view).getChildAt(x);

            if (positionsLeft_whiteKeys.size() >= 0 && positionsRight_whiteKeys.size() >= 0)
            {
                if (positionX > positionsLeft_whiteKeys.get(x) && positionX < positionsRight_whiteKeys.get(x))
                {
                    pianoKey = (FrameLayout) ((LinearLayout) view).getChildAt(x);

                    if (pianoKey != null)
                    {
                        pianoKey.setBackgroundResource(R.drawable.dinger14);
                        pressedKeys.add(pianoKey);
                    }
                    if (lastPlayedKey != pianoKey)
                        playKey(pitch);

                    lastPlayedKey = pianoKey;
                    break;
                }

                if (lastPlayedKey != null)
                {
                    pianoKey.setBackgroundResource(R.drawable.dinger14);
                    lastPlayedKey.setBackgroundResource(R.drawable.dinger14);

                }
            }
        }

        if (motionEvent.getAction() == MotionEvent.ACTION_UP)
        {
            lastPlayedKey = null;

            for (FrameLayout pressedKey : pressedKeys)
            {
                pressedKey.setBackgroundResource(R.drawable.dinger14);
            }


        }

        return false;
    }
};


//This is sound play method
SoundPool   sp = new SoundPool(1, AudioManager.STREAM_MUSIC, 1);
public void playKey(final float pitch)
{

    //here you should store your piano sound at res/raw then load it
    sp.load(this, R.raw.chitare3, 1);

    sp.setOnLoadCompleteListener(new SoundPool.OnLoadCompleteListener()
    {
        @Override
        public void onLoadComplete(SoundPool soundPool, int i, int i2)
        {
            soundPool.play(i, 0.99f, 0.99f, 1, 0, pitch);
        }
    });
}