在Android中触摸屏幕时触摸事件

Question

我正在尝试使用以下代码在Android自定义视图中实现基本虚拟操纵杆。

this.setOnTouchListener(new OnTouchListener() {
        @Override
        public boolean onTouch(View arg0, MotionEvent e) {
            switch(e.getAction()){
                case(MotionEvent.ACTION_DOWN):
                    moving = true;
                    joystickVisibility = true;
                    joystickCoordinates[0] = (int) e.getX() - imageJoystick.getWidth() / 2;
                    joystickCoordinates[1] = (int) e.getY() - imageJoystick.getHeight() / 2;
                    joystickBaseCoordinates[0] = (int) e.getX() - imageJoystickBase.getWidth() / 2;
                    joystickBaseCoordinates[1] = (int) e.getY() - imageJoystickBase.getHeight() / 2;
                    break;
                case(MotionEvent.ACTION_MOVE):
                    joystickCoordinates[0] = (int) e.getX() - imageJoystick.getWidth() / 2;
                    joystickCoordinates[1] = (int) e.getY() - imageJoystick.getHeight() / 2;
                    if (joystickCoordinates[0] > joystickBaseCoordinates[0] + 50)
                        joystickCoordinates[0] = joystickBaseCoordinates[0] + 50;
                    if (joystickCoordinates[0] < joystickBaseCoordinates[0] - 50)
                        joystickCoordinates[0] = joystickBaseCoordinates[0] - 50;
                    if (joystickCoordinates[1] > joystickBaseCoordinates[1] + 50)
                        joystickCoordinates[1] = joystickBaseCoordinates[1] + 50;
                    if (joystickCoordinates[1] < joystickBaseCoordinates[1] - 50)
                        joystickCoordinates[1] = joystickBaseCoordinates[1] - 50;
                    break;
                case(MotionEvent.ACTION_UP):
                    moving = false;
                    joystickVisibility = false;
                    break;
                }
            move();
            postInvalidate();
            return true;
            }
    });

除非操纵杆朝一个方向但未被移动，否则它正在工作。 在触摸屏幕时，我找不到任何有效的事件。