问android画布使用重影绘制形状

EN

if (chosenShape.equals("rectangle")) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN: // user start pressing
            //starting point - one side of the rect
            starting_X = touchX;
            starting_Y = touchY;
            break;
        case MotionEvent.ACTION_MOVE: // user move while pressing

            break;
        case MotionEvent.ACTION_UP: // user release
            //ending point - thie side of the circle
            ending_X = touchX;
            ending_Y = touchY;
            // draw the rectangle - opposite side of the rect
            drawCanvas.drawRect(starting_X, starting_Y, ending_X, ending_Y, drawPaint);
            chosenShape = ""; // reseting the shape to keep drawing
            break;
        default:
            return false;

    }
} else {
    switch (event.getAction()) {

        case MotionEvent.ACTION_DOWN:
            drawPath.moveTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_MOVE:
            drawPath.lineTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_UP:
            drawCanvas.drawPath(drawPath, drawPaint);
            drawPath.reset();
            break;
        default:
            return false;
    }
}