Change z-order of Fragments during ongoing FragmentTransaction

android, android-animation, android-fragments, fragmenttransaction

Solution

I also had this problem and the only workaround I have been able to find is to place another FrameLayout directly under the one that holds the current fragment. Then I transition my new fragment into the alternate FrameLayout (which has a higher z-ordering than the FrameLayout below it) and remove the old fragment from the original FrameLayout in the same transaction. Something like this:

<FrameLayout
    android:id="@+id/video_list_frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</FrameLayout>

<FrameLayout
    android:id="@+id/video_player_frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</FrameLayout>

Yes, I know this adds an additional view to the hierarchy but it doesn't increase the tree depth. For additional performance boost I override onCreateAnimator in my fragments to offload the animation to the hardware layer, like so:

@Override
public Animator onCreateAnimator(int transit, boolean enter, int nextAnim) {
    Animator animation = super.onCreateAnimator(transit, enter, nextAnim);

    // HW layer support only exists on API 11+
    if (Build.VERSION.SDK_INT >= 11) {
        if (animation == null && nextAnim != 0) {
            animation = AnimatorInflater.loadAnimator(getActivity(), nextAnim);
        }

        if (animation != null) {
            animation.addListener(new LayerEnablingAnimatorListener(getView()));
        }
    }

    return animation;
}

And this is LayerEnablingAnimatorListener:

public class LayerEnablingAnimatorListener extends AnimatorListenerAdapter {

    private final View mTargetView;
    private int mLayerType;

    public LayerEnablingAnimatorListener(View targetView) {
        mTargetView = Objects.requireNonNull(targetView, "Target view cannot be null");
    }

    public View getTargetView() {
        return mTargetView;
    }

    @Override
    public void onAnimationStart(Animator animation) {
        super.onAnimationStart(animation);
        mLayerType = mTargetView.getLayerType();
        mTargetView.setLayerType(View.LAYER_TYPE_HARDWARE, null);
    }

    @Override
    public void onAnimationEnd(Animator animation) {
        super.onAnimationEnd(animation);
        mTargetView.setLayerType(mLayerType, null);
    }
}

Problem

Original source