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android - 恢复Android状态时崩溃-无法转换AbsSavedState

我从Crashlytics收到有关Xamarin.Forms项目中以下崩溃的通知:

Fatal Exception: java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.xxx.xxx/xxxxx.MainActivity}:
java.lang.ClassCastException: android.view.AbsSavedState$1 cannot be cast to
android.widget.CompoundButton$SavedState
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2957)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032)
at android.app.ActivityThread.-wrap11(Unknown Source)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6944)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

Caused by java.lang.ClassCastException:
android.view.AbsSavedState$1 cannot be cast to android.widget.CompoundButton$SavedState
at android.widget.CompoundButton.onRestoreInstanceState(CompoundButton.java:619)
at android.view.View.dispatchRestoreInstanceState(View.java:18884)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3936)
at android.view.View.restoreHierarchyState(View.java:18862)
at com.android.internal.policy.PhoneWindow.restoreHierarchyState(PhoneWindow.java:2248)
at android.app.Activity.onRestoreInstanceState(Activity.java:1153)
at android.app.Activity.performRestoreInstanceState(Activity.java:1108)
at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1266)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2930)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032)
at android.app.ActivityThread.-wrap11(Unknown Source)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6944)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
  • 不幸的是，我无法复制它。
  • 我检查了CompoundButton是Switch的基类，并且我在主页上有两个开关。
  • 我只有一项主要 Activity 。
  • 我使用Xamarin.Forms，但Xamarin.Android中没有任何自定义布局。
  • 对于状态保存/恢复，我没有任何自定义操作。
  • 我检查了Xamarin.Forms的SwitchRenderer源代码及其基类，但也看不到任何状态保存代码。

    • 在有关Stack Overflow的许多问题中，都声称该问题可能是由重复的android:id引起的，但是如上所述，我没有自定义布局。

    更新

    我决定进行更深入的调查，并开始验证整个状态的保存机制。以下是我的发现:
  • 我发现整个 View 层次结构以对(viewId, state)的形式存储。事实证明，所有 View 都将状态保留为AbsSavedState，而CompoundButton存储CompoundButton.SavedState。因此，我的猜测是使用某种不正确的状态来还原CompoundButton。样本状态:
    • {Bundle[{  android:viewHierarchyState=Bundle[{android:views=
{1=android.view.AbsSavedState$1@e738983,2=android.view.AbsSavedState$1@e738983,
3=android.view.AbsSavedState$1@e738983, 4=android.view.AbsSavedState$1@e738983,
5=android.view.AbsSavedState$1@e738983, 6=android.view.AbsSavedState$1@e738983,
7=android.view.AbsSavedState$1@e738983, 8=android.view.AbsSavedState$1@e738983,
9=android.view.AbsSavedState$1@e738983, 10=android.view.AbsSavedState$1@e738983,
11=android.view.AbsSavedState$1@e738983, 12=android.view.AbsSavedState$1@e738983,
13=android.view.AbsSavedState$1@e738983, 14=android.view.AbsSavedState$1@e738983,
15=android.view.AbsSavedState$1@e738983, 16=android.view.AbsSavedState$1@e738983,
17=android.view.AbsSavedState$1@e738983, 18=android.view.AbsSavedState$1@e738983,
19=android.view.AbsSavedState$1@e738983, 20=android.view.AbsSavedState$1@e738983,
21=android.view.AbsSavedState$1@e738983, 22=android.view.AbsSavedState$1@e738983,
23=android.view.AbsSavedState$1@e738983, 24=CompoundButton.SavedState{26e683d checked=false},
25=android.view.AbsSavedState$1@e738983, 26=CompoundButton.SavedState{8f32832 checked=true},
27=android.view.AbsSavedState$1@e738983, 28=android.view.AbsSavedState$1@e738983,
29=android.view.AbsSavedState$1@e738983, 30=android.view.AbsSavedState$1@e738983,
31=android.view.AbsSavedState$1@e738983, 32=android.view.AbsSavedState$1@e738983,
33=android.view.AbsSavedState$1@e738983, 34=android.view.AbsSavedState$1@e738983,
35=android.view.AbsSavedState$1@e738983, 36=android.view.AbsSavedState$1@e738983,
37=android.view.AbsSavedState$1@e738983,
16908290=android.view.AbsSavedState$1@e738983,
2131558525=android.view.AbsSavedState$1@e738983,
2131558526=android.view.AbsSavedState$1@e738983}}],
android:lastAutofillId=1073741825,
android:fragments=android.app.FragmentManagerState@969a700}]}
    1. I've got CompoundButtons (base class for Switch) on two pages: MainPage and modal page. After all I thought that maybe this possible mismatch while restoring state is caused by duplicated ids somehow. I decided to write a piece of code to print whole hierarchy with ids. Below you can see MainPage and modal page, in total 3 switches. However, there is no duplication here.
    -- 16908290 - ContentFrameLayout
---- -1 - RelativeLayout
------ -1 - PlatformRenderer
-------- 1 - PageRenderer
---------- -1 - DefaultRenderer
------------ -1 - DefaultRenderer
-------------- 2 - ImageRenderer
------------ -1 - CustomScrollViewRenderer
-------------- -1 - ScrollViewContainer
---------------- -1 - DefaultRenderer
------------------ -1 - DefaultRenderer
-------------------- -1 - DefaultRenderer
---------------------- -1 - DefaultRenderer
------------------------ 3 - ImageRenderer
---------------------- 4 - LabelRenderer
---------------------- 5 - LabelRenderer
---------------------- -1 - DefaultRenderer
------------------------ 6 - ImageRenderer
------------------ -1 - DefaultRenderer
-------------------- -1 - DefaultRenderer
---------------------- 7 - LabelRenderer
---------------------- 8 - LabelRenderer
---------------------- -1 - DefaultRenderer
------------------------ 9 - ImageRenderer
------------------ -1 - DefaultRenderer
-------------------- -1 - DefaultRenderer
---------------------- -1 - DefaultRenderer
------------------------ -1 - GaugeChartRenderer
------------------------ 10 - LabelRenderer
------------------------ 11 - LabelRenderer
------------------------ -1 - GaugeChartRenderer
------------------------ 12 - LabelRenderer
------------------------ 13 - LabelRenderer
------------------ -1 - DefaultRenderer
-------------------- 14 - LabelRenderer
-------------------- 15 - LabelRenderer
------------------ -1 - LinearChartRenderer
-------------------- 16 - LinearChart
------------------ -1 - DefaultRenderer
-------------------- -1 - CustomButtonRenderer
---------------------- 17 - Button
-------------------- -1 - CustomButtonRenderer
---------------------- 18 - Button
-------------------- -1 - CustomButtonRenderer
---------------------- 19 - Button
-------------------- -1 - CustomButtonRenderer
---------------------- 20 - Button
-------------------- -1 - CustomButtonRenderer
---------------------- 21 - Button
-------------------- -1 - CustomButtonRenderer
---------------------- 22 - Button
------------------ -1 - DefaultRenderer
------------------ -1 - DefaultRenderer
-------------------- -1 - DefaultRenderer
---------------------- 23 - LabelRenderer
---------------------- 24 - LabelRenderer
---------------------- 25 - LabelRenderer
---------------------- 26 - LabelRenderer
---------------------- 27 - LabelRenderer
-------------------- -1 - DefaultRenderer
---------------------- -1 - DefaultRenderer
------------------------ -1 - DefaultRenderer
-------------------------- 33 - LabelRenderer
-------------------------- 34 - LabelRenderer
-------------------------- 35 - LabelRenderer
------------------ -1 - DefaultRenderer
-------------------- -1 - CustomSwitchRenderer
---------------------- 28 - Switch
-------------------- 29 - LabelRenderer
-------------------- -1 - DefaultRenderer
---------------------- 36 - ImageRenderer
------------------ -1 - DefaultRenderer
-------------------- -1 - CustomSwitchRenderer
---------------------- 30 - Switch
-------------------- 31 - LabelRenderer
------------------ -1 - DefaultRenderer
-------------------- 37 - ImageRenderer
-------------------- -1 - CustomButtonRenderer
---------------------- 32 - Button
-------- 44 - ModalContainer
---------- -1 - View
---------- 38 - PageRenderer
------------ -1 - DefaultRenderer
-------------- -1 - DefaultRenderer
---------------- -1 - DefaultRenderer
------------------ 39 - LabelRenderer
------------------ -1 - DefaultRenderer
-------------------- 45 - ImageRenderer
---------------- -1 - SearchBarRenderer
------------------ 40 - SearchView
-------------------- 16909226 - LinearLayout
---------------------- 16909225 - AppCompatTextView
---------------------- 16909227 - AppCompatImageView
---------------------- 16909229 - LinearLayout
------------------------ 16909231 - AppCompatImageView
------------------------ 16909232 - LinearLayout
-------------------------- 16909233 - AutoCompleteTextView
-------------------------- 16909228 - AppCompatImageView
------------------------ 16909321 - LinearLayout
-------------------------- 16909230 - AppCompatImageView
-------------------------- 16909235 - AppCompatImageView
-------------- -1 - DefaultRenderer
---------------- -1 - ListViewRenderer
------------------ -1 - SwipeRefreshLayout
-------------------- 41 - ListView
---------------------- -1 - Container
---------------------- -1 - Container
------------------------ -1 - DefaultRenderer
-------------------- -1 - ImageView
-------------- -1 - DefaultRenderer
---------------- -1 - DefaultRenderer
------------------ -1 - CustomSwitchRenderer
-------------------- 42 - Switch
------------------ 43 - LabelRenderer
    1. Later I thought that maybe Xamarin's id generation mechanism fails after state restoration. But I checked it and after restoration it is properly increased. I even checked source code in Xamarin.Forms/Platform.cs: 
    internal static int GenerateViewId()
{
    if ((int)Build.VERSION.SdkInt >= 17)
        return global::Android.Views.View.GenerateViewId();
    if (s_id >= 0x00ffffff)
        s_id = 0x00000400;
    return s_id++;
}

static int s_id = 0x00000400;

    It looks fine, unless there is some race condition. I'm running out of ideas.

    Update 2

    I subclassed Switch control and overrode OnRestoreSavedInstance and strange thing that it's never called on my devices. However, OnSaveInstanceState is called. Please mind that I properly simulated state restoration (it is called in MainActivity, but doesn't propagate to Switch).

    I found the reason why it behaves in this way. Please take a look at Android's implementation for View.dispatchRestoreState:

    protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container)
{
    if (mID != NO_ID) {
        Parcelable state = container.get(mID);  // <--- HERE
        if (state != null) {
            // Log.i("View", "Restoreing #" + Integer.toHexString(mID)
            // + ": " + state);
            mPrivateFlags &= ~SAVE_STATE_CALLED;
            onRestoreInstanceState(state);
            if ((mPrivateFlags & SAVE_STATE_CALLED) == 0) {
                throw new IllegalStateException(
                        "Derived class did not call super.onRestoreInstanceState()");
            }
        }
    }
}

    Xamarin.Forms通过增加计数器自动设置ID。因此，在创建页面后，它将ids从1设置为n。再次娱乐(例如，旋转屏幕后)后，它将ids从n+1设置为2n+1。因此，没有一个控件能够恢复其状态，因为在保留状态时，它将被另存为id=x的状态，但是，在重新创建Activity之后，此控件将具有不同的id。

    因此，由于没有状态恢复，永远不会发生此崩溃。

    更新3

    我还注意到Android实现中的一些奇怪之处。 CompoundButton具有以下实现:
    @Override
public void onRestoreInstanceState(Parcelable state) {
    SavedState ss = (SavedState) state;
    super.onRestoreInstanceState(ss.getSuperState());
    setChecked(ss.checked);
    requestLayout();
}

    但是，TextView(CompoundButton的祖先)具有以下实现:
    @Override
public void onRestoreInstanceState(Parcelable state) {
    if (!(state instanceof SavedState)) {
        super.onRestoreInstanceState(state);
        return;
    }
    SavedState ss = (SavedState) state;
    super.onRestoreInstanceState(ss.getSuperState());

    // ...
}

    如您所见，TextView首先验证此转换是否成功，CompoundButton无效。也许这是Android中的缺陷。但是我仍然看不到状态不匹配以及AbsSavedState传递给CompoundButton而不是CompoundButton.SavedState的可能性。

    最佳答案

    这不能解决您的总体问题，但是我相信我可以为您的 Update 3 部分提供一些帮助。

    首先让我重申一下您的问题:为什么TextView和CompoundButton具有两种不同的实现onRestoreInstanceState()的策略？

    TextView根据传递给它的特定Parcelable执行条件逻辑:



    尽管CompoundButton不会:



    原因是TextView和CompoundButton具有两种不同的实现onSaveInstanceState()的策略，因此每个类都有相应的策略来恢复状态。

    TextView可以从onSaveInstanceState()返回两种不同的类型:



    只有在SavedState调用无法保存所需的所有内容的情况下(例如，当TextView被要求卡住其文本或具有选择内容时)，TextView才会返回其自己的自定义super类。在所有其他情况下，它仅委托(delegate)给super调用并直接返回该调用。

    由于onRestoreInstanceState()将接收返回的任何onSaveInstanceState()，因此TextView在接收super返回值或自己的SavedState时需要能够工作。

    另一方面，CompoundButton只能从onSaveInstanceState()返回一种类型:



    因为我们知道传入的state对象将始终为SavedState类型，所以我们不必执行任何条件逻辑。我们可以将其抛弃。

    希望此答案为其他回答者可以建立的基础，并可能最终回答您的主要问题。

    关于android - 恢复Android状态时崩溃-无法转换AbsSavedState，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/53497612/

    10-12 02:00
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