Android 拖动过程中的动画 Alpha Animation 现在工作

Question

I've added the drag functionality to a component using ViewDragHelper and I'm trying to add a fade animation to the component so that when the user touches the screen and drag it, it changes the component's alpha using an animation. The problem is that the animation waits for the user's interaction to stop and then it applies the animation so that during the component transition, you can't see the alpha animation,

override fun clampViewPositionVertical(child: View, top: Int, dy: Int): Int {
        if(top < verticalRange)
            return verticalRange
        backgroundView.animate().alpha((backgroundView.alpha - 0.05).toFloat()).duration = 10
        return top
    }

The on touch Event:

 override fun onTouchEvent(event: MotionEvent): Boolean {
            return if (isDragEnabled && (isControlScreenLayoutTarget(event) || isMoving)) {
                viewDragHelper.processTouchEvent(event)
                true
            } else {
                super.onTouchEvent(event)
            }
        }

Answer 1

You should not start your animation in clampViewPositionVertical() . That method is called to return the boundaries where the view will move, actually scroll.

Instead you should wait until view is released, in other words, start your animation as soon as the range check is fulfilled in the onViewReleased() .