android - 快速点击 Android 的概览按钮两次时出现内部异常/崩溃

Question

我有一个名为 CustomArFragment 的 fragment (ArFragment from Sceneform 1.15 的子类)包含在 MainActivity 中。在某个时间点，我通过替换为新实例来重置 fragment 。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，替换一开始似乎工作正常，新 fragment 在替换后照常运行。但是，如果我在调用 reset() 后的任何时间点按 android overview button 快速连续两次 我收到以下错误，这似乎与一些我无法追踪的内部调用有关:

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 fragment 的方式有问题。

我想澄清一下，除非我在替换完成后双击应用程序概览按钮，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，如果我按下概览按钮，然后等待一两秒钟，然后再次按下它以打开应用程序备份，一切都会按预期运行而不会崩溃。

非常感谢您的帮助，我已经想不出是什么原因造成的!

Answer 1

崩溃似乎与某些 ARCore/Sceneform 资源在删除旧 fragment 后保持运行一段时间有关，但仍然引用删除的 fragment (前一段时间我解决了这个问题，所以我不记住确切的原因，但我认为是这个)。

无论如何，为了避免崩溃，我发现唯一可行的方法是将删除的 fragment 添加到后台堆栈。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 fragment 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 fragment 的重置次数会很低，所以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。