快速点击Android的概述按钮两次时出现内部异常/崩溃

Question

我在 MainActivity 中包含一个名为 CustomArFragment(来自 Sceneform 1.15 的 ArFragment 的子类(的片段。在某个时间点，我通过替换为新实例来重置片段。我通过在 MainActivity 中调用以下方法来执行此操作：

fun reset() {
val oldFragment = (supportFragmentManager.findFragmentById(R.id.custom_ar_fragment)) as? CustomArFragment ?: return
val newArFragment = CustomArFragment()
val transaction = supportFragmentManager.beginTransaction()
transaction.remove(oldFragment)
transaction.add(R.id.custom_ar_fragment, newArFragment)
transaction.commit()
}

现在，正如我所说，替换起初似乎工作正常，并且新片段在更换后照常运行。但是，如果我在调用reset()后的任何时间点快速连续两次按下android概述按钮，我会收到以下错误，该错误似乎与我无法跟踪的一些内部呼叫有关：

java.lang.NullPointerException: throw with null exception
at com.google.ar.sceneform.utilities.Preconditions.checkNotNull(SourceFile:3)
at com.google.ar.sceneform.SceneView.onLayout(SourceFile:41)
at com.google.ar.sceneform.ArSceneView.onLayout(SourceFile:79)
at android.view.View.layout(View.java:20729)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:757)
at android.view.View.layout(View.java:20729)
at android.view.ViewGroup.layout(ViewGroup.java:6198)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2859)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2386)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1524)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7398)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1092)
at android.view.Choreographer.doCallbacks(Choreographer.java:888)
at android.view.Choreographer.doFrame(Choreographer.java:819)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1078)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:201)
at android.app.ActivityThread.main(ActivityThread.java:6815)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)

现在，我不确定这是与Sceneform相关的错误，还是我替换片段的方式有问题。

我想澄清一下，除非我在替换发生后双击应用程序概述按钮，否则替换工作正常，并且我没有在 CustomArFragment 的生命周期方法中执行任何可能干扰替换的操作。因此，如果我按下概述按钮，然后等待一两秒钟，然后再次按下它以打开应用程序备份，则一切都按预期工作而不会崩溃。

非常感谢帮助，我已经用完了可能导致这种情况的想法！

Answer 1

崩溃似乎与以下事实有关：某些 ARCore/Sceneform 资源在删除旧片段后保持运行一段时间，但仍引用已删除的片段(不久前我解决了这个问题，所以我不记得确切的原因，但我认为是这个(。

无论如何，为了避免崩溃，我发现唯一有效的方法是将删除的片段添加到后堆栈中。这样，sceneform/ARCore 就不会遇到空指针。

val oldFragment = (supportFragmentManager.findFragmentById(R.id.custom_ar_fragment)) as? CustomArFragment ?: return
oldFragment.arSceneView.pause()
val newArFragment = CustomArFragment()
val transaction = supportFragmentManager.beginTransaction().remove(oldFragment).add(R.id.sceneform_fragment, newArFragment).addToBackStack(null)
transaction.commit()
supportFragmentManager.executePendingTransactions()

当然，将旧片段保存到后台堆栈并不理想，因为我从不打算返回它们。但是，由于我假设片段的重置次数会很低，因此它对我来说已经足够好了。但是，如果您找到重置ArFragment的更好解决方案，请告诉我。