FAB没有动画-测试代码和截图已附加

我已经准备好了 a simple test project at GitHub 对于我的问题:

我试图显示/隐藏 FloatingActionButton (又名FAB)每5秒通过以下代码 MainActivity.java :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mFab = (FloatingActionButton) findViewById(R.id.fab);

    mInAnimation = AnimationUtils.makeInAnimation(this, false);
    mInAnimation.setAnimationListener(new Animation.AnimationListener() {
        @Override
        public void onAnimationEnd(Animation animation) {
        }

        @Override
        public void onAnimationRepeat(Animation animation) {
        }

        @Override
        public void onAnimationStart(Animation animation) {
            mFab.setVisibility(View.VISIBLE);
        }
    });

    mOutAnimation = AnimationUtils.makeOutAnimation(this, true);
    mOutAnimation.setAnimationListener(new Animation.AnimationListener() {
        @Override
        public void onAnimationEnd(Animation animation) {
            mFab.setVisibility(View.INVISIBLE);
        }

        @Override
        public void onAnimationRepeat(Animation animation) {
        }

        @Override
        public void onAnimationStart(Animation animation) {
        }
    });

    run();
}

这个 Runnable 输出(“切换动画”)在ADB日志中每5秒出现一次,但FAB始终可见:

@Override
public void run() {
    Log.d("MyCoordinator", "Toggle animation");
    mFab.setAnimation(mFab.isShown() ? mOutAnimation : mInAnimation);
    mHandler.postDelayed(this, 5000);
}

有人知道这里缺什么吗?

我也很好奇,是否可以在 activity_main.xml 而不是Java代码。