问画布；如何追溯删除形状

EN

objectA.delete();
objectB.delete();

switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
   /// get the child that corresponds to the first touch
    DotView objectA = getChildForTouch((TableLayout) v, x, y);

    return true;
 case MotionEvent.ACTION_MOVE:

 ///used the x - y to get the object for every other  shape the user`S finger passes over.
 DotView objectB = getChildForTouch((TableLayout) v, x, y);


   /// just update positions
   line.setCoords(mStartX, mStartY, (int) x, (int) y);

 objectA.delete(); ///Delete first shape
 objectB.delete(); ///Delete second shape

break;

case MotionEvent.ACTION_UP:
    ///Gets the last shape where the user released their fingers
    endView = getChildForTouch((TableLayout) v, x, y);
break;

private static class DotView extends View {

        private static final int DEFAULT_SIZE = 100;
        private Paint mPaint = new Paint();
        private Rect mBorderRect = new Rect();
        private Paint mCirclePaint = new Paint();
        private int mRadius = DEFAULT_SIZE / 4;

        public DotView(Context context) {
            super(context);
            mPaint.setStrokeWidth(2.0f);
            mPaint.setStyle(Style.STROKE);
            mPaint.setColor(Color.RED);
            mCirclePaint.setColor(Color.CYAN);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.drawColor(Color.parseColor("#0099cc"));
            mBorderRect.left = 0;
            mBorderRect.top = 0;
            mBorderRect.right = getMeasuredWidth();
            mBorderRect.bottom = getMeasuredHeight();
            canvas.drawRect(mBorderRect, mPaint);
            canvas.drawCircle(getMeasuredWidth() / 2, getMeasuredHeight() / 2,
                    mRadius, mCirclePaint);
        }


        public void delete(){
        mPaint.setColor(Color.TRANSPARENT);
        }

    }