How to create a Scratch Card in Android?

I need to create a “Scratch Card” App for my final project in school and can’t find the way how to implement the scratching event (How do I create background image and put Grey rectangles over it, so when I will scratch those rectangles I will see the picture under them)

The Implementation must be in Android because I don’t how to develop In Objective-C yet.

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    My Code is:

    public class FingerPaint extends Activity {
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
    
            try {
                MyView myView = new MyView(this);
                myView.requestFocus();
                myView.PaintObjectInit();
                // setContentView(myView);
    
                LinearLayout upper = (LinearLayout) findViewById(R.id.LinearLayout01);
                upper.addView(myView);
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            }
    
            // MyImageView myImageView = new MyImageView(this);
            // setContentView(myImageView);
        }
    }
    
    
    
    public class MyView extends View {
    
        private Paint mPaint;
        private Bitmap mBitmap;
        private Canvas mCanvas;
        private Path mPath;
        private Paint mBitmapPaint;
    
        public MyView(Context context) {
            super(context);
            this.mPaint = new Paint();
            mPath = new Path();
            mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        }
    
        protected void PaintObjectInit() {
            mPaint.setAntiAlias(true);
            mPaint.setDither(true);
            //mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
            //mPaint.setColor(0xFFFF0000);
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setStrokeJoin(Paint.Join.ROUND);
            mPaint.setStrokeCap(Paint.Cap.ROUND);
            mPaint.setStrokeWidth(12);
        }
    
        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
    
            try
            {
    
    
            //Bitmap bm1 = BitmapFactory.decodeResource(this.getResources(),R.drawable.scratch).copy(Bitmap.Config.ARGB_8888, true);;
            //Bitmap bm2 = BitmapFactory.decodeResource(this.getResources(),R.drawable.main).copy(Bitmap.Config.ARGB_8888, true);;
    
            //mBitmap = toTransparency(bm1, 0xFFAAAAAA, true, bm2);
    
            mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);
            }
            catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            }
        }
    
        @Override
        protected void onDraw(Canvas canvas) {
    
            canvas.drawColor(0xFFAAAAAA);
            canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
            canvas.drawPath(mPath, mPaint);
        }
    
        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;
    
        private void touch_start(float x, float y) {
            // mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
        }
    
        private void touch_move(float x, float y) {
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
                mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
                mX = x;
                mY = y;
            }
        }
    
        private void touch_up() {
            mPath.lineTo(mX, mY);
            // commit the path to our offscreen
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw
            // mPath.reset();
        }
    
        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX();
            float y = event.getY();
    
            switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
            }
            return true;
        }
    }
    

    Please help regarding this.

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