Rotating FloatingActionButton

Question

I believe most of you all have seen the rotating FloatingActionButton in apps such as Google keep, push bullet and even Google inbox app. I am trying to achieve this rotation by

Answer 1

I found that on pre-Lollipop shadow is rotating, but on API >= 21 everything is right.

So, on pre-Lollipop I've tried to rotate an ImageView over FAB. And it works great.

Here is layout where we place ImageView with same source image over FAB:

    android:id="@+id/rotatingFab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end">

    

    

We start animation like this:

public void startAnimation(Animation animation) {
    if (Build.VERSION.SDK_INT >= 21) {
        mFab.startAnimation(animation);
    } else {
        mFabImage.setVisibility(VISIBLE);
        // need post() to image could measure its size
        mFabImage.post(() -> mFabImage.startAnimation(animation));
    }
}

And stop it:

public void clearAnimation() {
    if (Build.VERSION.SDK_INT >= 21) {
        mFab.clearAnimation();
    } else {
        mFabImage.clearAnimation();
        mFabImage.setVisibility(GONE);
    }
}

I wrap FrameLayout in custom view to more comfortable, here is full gist https://gist.github.com/pengrad/9db82de705b58b10c5e9