恢复Android状态时崩溃 - 无法强制转换AbsSavedState

Question

恢复Android状态时崩溃 - 无法强制转换AbsSavedState

Woj*_*lik 10 android xamarin xamarin.forms

我从Crashlytics收到有关我的Xamarin.Forms项目中的以下崩溃的通知:

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)

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不幸的是,我无法重现它.
我检查过这CompoundButton是一个基类,Switch我的主页上有两个开关.
我只有一个主要活动.
我在Xamarin.Android中没有任何自定义布局使用Xamarin.Forms.
我对状态保存/恢复没有任何自定义操作.
我检查了Xamarin.Forms源代码SwitchRenderer及其基类,我也没有看到任何状态保存代码.

在Stack Overflow的许多问题中,声称问题可能是由重复引起的android:id,但正如我上面提到的,我没有自定义布局.

更新

我决定深入调查,开始验证整个州的保全机制.以下是我的发现:

我发现整个视图层次结构都是成对存储的(viewId, state).事实证明,所有视图都将状态保留为AbsSavedState仅CompoundButton存储CompoundButton.SavedState.因此,我的猜测是,某种程度上错误的状态用于恢复CompoundButton.样品状态:

{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}]}

我有两个页面的CompoundButtons基类Switch:MainPage和模态页面.毕竟我认为这可能是这种可能的不匹配,而恢复状态是由重复的ID以某种方式引起的.我决定写一段代码用ids打印整个层次结构.下面你可以看到MainPage和模态页面,总共3个开关.但是,这里没有重复.

-- 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

后来我认为,在状态恢复后,Xamarin的id生成机制可能会失败.但我检查了它,并在恢复后适当增加.我甚至检查了Xamarin.Forms/Platform.cs中的源代码:

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;

它看起来很好,除非有一些竞争条件.我的想法已经不多了.

更新2

我将Switch控制和覆盖OnRestoreSavedInstance以及奇怪的东西分类,它从未在我的设备上调用过.然而,OnSaveInstanceState被称为.请注意,我正确地模拟了状态恢复(它被调用MainActivity,但不会传播到Switch).

我找到了它以这种方式表现的原因.请看一下Android的实现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()");
            }
        }
    }
}

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Xamarin.Forms通过增加计数器自动设置ID.因此,在创建页面后,它会将ID设置1为n.在另一次娱乐之后(例如在旋转屏幕之后),它将ID设置n+1为2n+1.因此,任何控件都无法恢复其状态,因为在保留状态时它将保存为状态id=x,但是在重新创建后,Activity此控件将具有不同的ID.

因此,不应该发生这种崩溃,因为没有状态恢复......

更新3

我注意到Android的实现中也有一些奇怪的东西.CompoundButton有这个实现:

@Override
public void onRestoreInstanceState(Parcelable state) {
    SavedState ss = (SavedState) state;
    super.onRestoreInstanceState(ss.getSuperState());
    setChecked(ss.checked);
    requestLayout();
}

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然而,TextView(CompoundButton's祖先)有这个实现:

@Override
public void onRestoreInstanceState(Parcelable state) {
    if (!(state instanceof SavedState)) {
        super.onRestoreInstanceState(state);
        return;
    }
    SavedState ss = (SavedState) state;
    super.onRestoreInstanceState(ss.getSuperState());

    // ...
}

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如您所见,TextView首先验证此演员表是否成功,CompoundButton不是.也许这是Android的缺陷.但是我仍然没有看到状态如何被错配并且AbsSavedState已经被传递给CompoundButton了CompoundButton.SavedState.

Answer 1

Woj*_*lik 2

毕竟，看起来必须有重复的 id 处于保留状态，但是我没有看到任何合理的解释。我也无法在我的设备上重现它。正如我上面所描述的：

Xamarin.Forms 通过增加计数器自动设置 ids。因此，在创建页面后，它将 id 设置1为n。在另一次游戏后（例如旋转屏幕后），它将 id 设置n+1为2n+1。因此，没有控件能够恢复其状态，因为在保留状态时，它将被保存为 id=x 的状态，但是在重新创建 Activity 后，该控件将具有不同的 id。

尽管如此，我还是找到了一种解决方法来阻止崩溃。

using Android.Content;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(Switch), typeof(MyApp.Droid.CustomRenderers.CustomSwitchRenderer))]
namespace MyApp.Droid.CustomRenderers
{
    public class CustomSwitchRenderer : SwitchRenderer
    {
        public CustomSwitchRenderer(Context context) : base(context)
        {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<Switch> e)
        {
            base.OnElementChanged(e);

            if (this.Control != null)
            {
                this.Control.Id = -1;
                this.Control.SaveEnabled = false;
            }
        }
    }
}

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它禁用所有控件的状态保存Switch。以防万一我还设置Id = -1覆盖 Xamarin 分配的 id。-1是 Android 中的常量，表示“无 id”。

此解决方法不会破坏中的状态保存Xamarin.Forms，因为Page重新创建后的状态依赖于您的绑定，而不是 Android 的机制。

但是，如果您想让它在不禁用状态保存的情况下工作。您可以设置一些大 ID，该 ID 在运行之间保持不变。当然，您需要为每个设置不同的 ID Switch，因此您可能需要创建一个自定义Switch并添加一些属性，例如AndroidId. 请注意，id 应小于0x00ffffff且足够大，以避免与 Xamarin 自动生成的 id 发生冲突。

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