How to Implement single Touch and MultiTouch in Application?

Question 1

Ok , I make some thing like that , i force to make multi-touch on device which doesn't support multi-touch to my implementation was i create array that will hold the keys that you are clicked and loop on each of them in array and make the sound and don't to forget empty the array in the last

 View view = findViewById(R.id.imagebutton1);
        view.setOnTouchListener(this);
       view.setTag(1);
        View view2 = findViewById(R.id.imagebutton2);
        view2.setOnTouchListener(this);
        view2.setTag(2);

and so on for each view of you add tag

and make globe array

  boolean touchedViews [] = new boolean [viewsNumber];

and in touch event make the code below

 public boolean onTouch(View v, MotionEvent event) {
                    int action = event.getAction()

            synchronized (this) {                   

       switch (action) {
             case MotionEvent.ACTION_DOWN:// when you touch down

                 touchedViews[ (Integer) v.getTag()] = true;

                 break ;
             case case MotionEvent.ACTION_UP: // when you touch up
                 break;
             }

            }

            for(int i=0 ; i < touchedViews.length ; i++){
                // play sound of each view with true touch 
            }
        }

Question 2

You should read Handling Multi-Touch Gestures

Android work multitouch button also seems as if it solves the same issue.

Question 3

Note : some variables will not be declared in my code but its name very obvious for you to add their declaration

first of all you will implement custom view that will hold piano keyboard and add all keys on your own style and Load your sounds and declare the Paints in

**  protected void onLayout(boolean changed, int left, int top, int right, int bottom)**

and draw your keys with paints in ondraw method

 protected void onDraw(Canvas canvas)

and here the implementation of the Ontouch event and it support mutli-touch keys

    @Override
public boolean onTouchEvent(MotionEvent event) {
    int pointerCount = event.getPointerCount();
    int cappedPointerCount = pointerCount > MAX_FINGERS ? MAX_FINGERS : pointerCount;
    int actionIndex = event.getActionIndex();
    int action = event.getActionMasked();
    int id = event.getPointerId(actionIndex);

    if ((action == MotionEvent.ACTION_DOWN || action == MotionEvent.ACTION_POINTER_DOWN) && id < MAX_FINGERS) {
        mFingerPoints[id] = new Point((int) event.getX(actionIndex), (int) event.getY(actionIndex));
    } else if ((action == MotionEvent.ACTION_POINTER_UP || action == MotionEvent.ACTION_UP) && id < MAX_FINGERS) {
        mFingerPoints[id] = null;
        invalidateKey(mFingerTones[id]);
        mFingerTones[id] = -1;
    }

    for (int i = 0; i < cappedPointerCount; i++) {
        int index = event.findPointerIndex(i);
        if (mFingerPoints[i] != null && index != -1) {
            mFingerPoints[i].set((int) event.getX(index), (int) event.getY(index));
            int tone = getToneForPoint(mFingerPoints[i]);
            if (tone != mFingerTones[i] && tone != -1) {
                invalidateKey(mFingerTones[i]);
                mFingerTones[i] = tone;
                invalidateKey(mFingerTones[i]);
                if (!isKeyDown(i)) {
                    int poolIndex = mToneToIndexMap.get(mFingerTones[i]);
                    event.getPointerCoords(index, mPointerCoords);
                    float volume = mPointerCoords.getAxisValue(MotionEvent.AXIS_PRESSURE);
                    volume = volume > 1f ? 1f : volume;
                    mSoundPool.play(poolIndex, volume, volume, 0, 0, 1f);
                }
            }
        }
    }



    return true;
}