Grid lines on surfaceView android

[pancake leh]

I have a surfaceView which I use it to draw shapes on it. I would like to add in grid lines on my surfaceView before drawing the shapes on it. I have the onDraw method that draws a rectangle on the surfaceView shown below:

protected void onDraw(Canvas canvas) {
        // TODO Auto-generated method stub
        super.onDraw(canvas);

           Path path = new Path();
            path.moveTo(18,10);
            path.lineTo(1, 0);
            path.lineTo(0, 20);

            paint.setColor(Color.RED);
            paint.setStrokeWidth(2);
            paint.setStyle(Paint.Style.STROKE);


            canvas.drawPath(path, paint);

}

Also i have no clue about zooming in and out of the surfaceView so that the rectangle i have drawn is can be sized up or sized down and also shifting of the surface view after it is being zoomed in.

A button must be pressed down in order to perform the zoom in function i have wrote the following. Is it the correct way?

zoombutton.setOnTouchListener(new OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            if(event.getAction() == MotionEvent.ACTION_DOWN) {


            } else if (event.getAction() == MotionEvent.ACTION_UP) {

            }
            return false;
        }

Please advice. Thank you.