public class CustomView extends View {  private int lastX; private int lastY; private int startLeft; private int startRight; private int startTop; private int startBottom;  public CustomView(Context context, @Nullable AttributeSet attrs) { super(context, attrs); }  @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); //畫一個小球 Paint paint = new Paint(); paint.setStrokeWidth(30); paint.setColor(Color.parseColor("#FF0000")); paint.setAntiAlias(true); paint.setStyle(Paint.Style.FILL_AND_STROKE); canvas.drawCircle(getWidth()/2,getHeight()/2,30,paint); }  @Override public boolean onTouchEvent(MotionEvent event) { int action = event.getAction(); //獲取手機觸摸的坐標 int x = (int) event.getX(); int y = (int) event.getY(); switch (action){ case MotionEvent.ACTION_DOWN://按下,獲取小球初始的位置 startLeft = getLeft(); startRight = getRight(); startTop = getTop(); startBottom = getBottom(); lastX = x; lastY = y; break; case MotionEvent.ACTION_MOVE://移動,小球跟隨手指的移動 int offsetX = x - lastX; int offsetY = y - lastY; layout(getLeft()+offsetX,getTop()+offsetY,  getRight()+offsetX,getBottom()+offsetY); break; case MotionEvent.ACTION_UP://當手指抬起時,回到小球初始的位置 layout(startLeft, startTop, startRight, startBottom); break; } return true; }}