如何在android中处理视图动画？

Question

I'm in the process of learning Animation in android and I have several questions -

I have view that I animate based on some bool:

mainFab.setOnClickListener {

        isOpen = ViewAnimations.rotate(binding.mainFab, !isOpen)

        if (isOpen) {
            ViewAnimations.apply {
                showMenu(binding.shareFab)
            }
        } else {
            ViewAnimations.apply {
                hideMenu(binding.shareFab)
            }}

}

ViewAnimations methods:

fun rotateFab(view: View, isFabOpen: Boolean):  Boolean {
    view.animate()
        .rotation(if (isFabOpen) 1440f else 0f)
        .setDuration(2000)
        .setListener(object : AnimatorListenerAdapter() {
            override fun onAnimationEnd(animation: Animator?) {
                super.onAnimationEnd(animation)
                Log.d(TAG, "onAnimationEnd: ")
            }
        })
    return isFabOpen
}

fun showMenu(view: View) {
    view.visibility = View.VISIBLE
    view.alpha = 0f
    view.animate()
        .setDuration(2000)
        .setListener(object : AnimatorListenerAdapter() {
            override fun onAnimationEnd(animation: Animator?) {

                super.onAnimationEnd(animation)
            }
        })
        .alpha(1f)
        .start()
}

fun hideMenu(view: View) {
    view.animate()
        .setDuration(2000)
        .setListener(object : AnimatorListenerAdapter() {
            override fun onAnimationEnd(animation: Animator?) {
                view.visibility = View.GONE
                super.onAnimationEnd(animation)
            }
        }).alpha(0f)
        .start()

My questions are:

1. In showMenu function, why my animation doesn't work properly without the empty listener? It's working fine at the first time, but from the second time and on it does animate the view, but then set the alpha to 0/ view to gone.

2. Why the animation still working without .start() ? Is it mandatory to use it?

3. if I start animation by calling showMenu and then at the half way I'm calling hideMenu it just hide the view in very ugly way, there is a way to "reverse" the animation in more elegant way?

Answer 1

All yours problem is from over engineering. What is doing the object ViewAnimations ?

About question :

1. There is can not be problem in empty listener. There is a problem somewhere in your logic.
2. Without .start() animation can not be launched. If animation is starting so there again a problem somewhere in your logic.
3. ViewPropertyAnimator animation can perfect animate from semi-state to new state. I recommend you to start write animation from the beginning to be confident in all your steps.