SharedElement and custom EnterTransition causes memory leak

Question

Having a shared element animation and also a custom enter animation causes the activity to leak.

Any idea what might be the cause?

09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * com.feeln.android.activity.MovieDetailActivity has leaked: 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * GC ROOT android.app.ActivityThread$ApplicationThread.this$0 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.app.ActivityThread.mActivities 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.util.ArrayMap.mArray 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references array java.lang.Object[].[1] 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.app.ActivityThread$ActivityClientRecord.activity 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references com.feeln.android.activity.MovieDetailActivity.mActivityTransitionState 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.app.ActivityTransitionState.mEnterTransitionCoordinator 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.app.EnterTransitionCoordinator.mEnterViewsTransition 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.transition.TransitionSet.mParent 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.transition.TransitionSet.mListeners 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references java.util.ArrayList.array 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references array java.lang.Object[].[1] 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.transition.TransitionManager$MultiListener$1.val$runningTransitions (anonymous class extends android.transition.Transition$TransitionListenerAdapter) 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references android.util.ArrayMap.mArray 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references array java.lang.Object[].[2] 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * references com.android.internal.policy.impl.PhoneWindow$DecorView.mContext 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * leaks com.feeln.android.activity.MovieDetailActivity instance 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ [ 09-21 16:19:31.007 28269:31066 D/LeakCanary ] * Reference Key: af2b6234-297e-4bab-96e9-02f1c4bca171 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * Device: LGE google Nexus 5 hammerhead 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * Android Version: 5.1.1 API: 22 LeakCanary: 1.3.1 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ * Durations: watch=6785ms, gc=262ms, heap dump=8553ms, analysis=33741ms 09-21 16:19:31.007 28269-31066/com.sample.android D/LeakCanary﹕ [ 09-21 16:19:31.007 28269:31066 D/LeakCanary ]

To reproduce you need to have a big shared image animation and also a custom EnterAnimation and setEnterSharedElementCallback . All this are from the support library.

Here is how i set the EnterTransition:

private SharedElementCallback mCallback = new SharedElementCallback() {
    @Override
    public void onSharedElementStart(List<String> sharedElementNames, List<View> sharedElements, List<View> sharedElementSnapshots) {
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP)
        {
            if(sharedElements.size()>0)
                getWindow().setEnterTransition(makeEnterTransition(getWindow().getEnterTransition(), getSharedElement(sharedElements)));
        }
    }


    private View getSharedElement(List<View> sharedElements)
    {
        for (final View view : sharedElements)
        {
            if (view instanceof ImageView)
            {
                return view;
            }
        }
        return null;
    }
};

Answer 1

Case of leaks lies in TransitionManager.sRunningTransitions where each DecorView adds and never removes. DecorView has link to his Activity's Context. Because of sRunningTransitions is static field, it has permanent chain of references to Activity, which will never be collected by GC.

I don't known why TransitionManager.sRunningTransitions needs, but if you remove Activity's DecorView from it, your problem will be solved. Follow code is example, how do it. In your activity class:

@Override
protected void onDestroy() {
    super.onDestroy();
    removeActivityFromTransitionManager(Activity activity);
}

private static void removeActivityFromTransitionManager(Activity activity) {
    if (Build.VERSION.SDK_INT < 21) {
        return;
    }
    Class transitionManagerClass = TransitionManager.class;
    try {
        Field runningTransitionsField = transitionManagerClass.getDeclaredField("sRunningTransitions");
            runningTransitionsField.setAccessible(true);
        //noinspection unchecked
        ThreadLocal<WeakReference<ArrayMap<ViewGroup, ArrayList<Transition>>>> runningTransitions
                = (ThreadLocal<WeakReference<ArrayMap<ViewGroup, ArrayList<Transition>>>>)
                runningTransitionsField.get(transitionManagerClass);
        if (runningTransitions.get() == null || runningTransitions.get().get() == null) {
            return;
        }
        ArrayMap map = runningTransitions.get().get();
        View decorView = activity.getWindow().getDecorView();
        if (map.containsKey(decorView)) {
            map.remove(decorView);
        }
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
}