SharedElement和自定义EnterTransition导致内存泄漏

拥有共享元素动画和自定义输入动画会导致活动泄漏。

知道可能是什么原因吗？

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 ]

要重现，您需要有一个大的共享图像动画以及一个自定义 EnterAnimation 和 setEnterSharedElementCallback 。所有这些都来自支持库。

这是我设置 EnterTransition 的方法：

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;
    }
};

泄漏案例在于TransitionManager.sRunningTransitions其中每个DecorView添加并且从不删除。DecorView有他的链接Activity's Context。因为sRunningTransitions是静态字段，它具有永久的引用链Activity，永远不会被 GC 收集。

我不知道为什么 TransitionManager.Running Transitions 需要，但如果你删除Activity's DecorView从此，你的问题就会得到解决。下面的代码就是例子，怎么做。在您的活动课中：

@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();
    }
}