Embedding a Xamarin.Forms fragment in a fragment causing "child already has a parent" crash

Question

I'm working on a library that would allow you to use Xamarin.Forms Pages with the native navigation service provided by MvvmCross.

The Android implementation has an issue when using Fragments. If you look at the library / sample project a crash occurs when you press the back button after loading the second fragment.

Steps to Reproduce:

1. Launch App
2. Press "Fragment Navigation Stack"
3. Press "Next"
4. Press the back button.

I've been pulling my hair out trying to figure out how to stop this error from occurring.

The app crashes with this error.

Java.Lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
  --- End of managed Java.Lang.IllegalStateException stack trace ---
java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
    at android.view.ViewGroup.addViewInner(ViewGroup.java:5106)
    at android.view.ViewGroup.addView(ViewGroup.java:4935)
    at android.view.ViewGroup.addView(ViewGroup.java:4875)
    at android.view.ViewGroup.addView(ViewGroup.java:4848)
    at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:326)
    at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1199)
    at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1368)
    at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1446)
    at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1509)
    at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)
    at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2181)
    at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2004)
    at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1959)
    at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1861)
    at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:2641)
    at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:2589)
    at androidx.fragment.app.Fragment.performActivityCreated(Fragment.java:2723)
    at androidx.fragment.app.FragmentStateManager.activityCreated(FragmentStateManager.java:346)
    at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1200)
    at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1368)
    at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1446)
    at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1509)
    at androidx.fragment.app.BackStackRecord.executePopOps(BackStackRecord.java:510)
    at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2178)
    at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2004)
    at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1959)
    at androidx.fragment.app.FragmentManager.popBackStackImmediate(FragmentManager.java:670)
    at androidx.fragment.app.FragmentManager.popBackStackImmediate(FragmentManager.java:581)
    at androidx.fragment.app.FragmentManager.handleOnBackPressed(FragmentManager.java:553)
    at androidx.fragment.app.FragmentManager$1.handleOnBackPressed(FragmentManager.java:350)
    at androidx.activity.OnBackPressedDispatcher.onBackPressed(OnBackPressedDispatcher.java:192)
    at androidx.activity.ComponentActivity.onBackPressed(ComponentActivity.java:314)
    at android.app.Activity.onKeyUp(Activity.java:3641)
    at android.view.KeyEvent.dispatch(KeyEvent.java:2825)
    at android.app.Activity.dispatchKeyEvent(Activity.java:3958)
    at androidx.core.app.ComponentActivity.superDispatchKeyEvent(ComponentActivity.java:122)
    at androidx.core.view.KeyEventDispatcher.dispatchKeyEvent(KeyEventDispatcher.java:84)
    at androidx.core.app.ComponentActivity.dispatchKeyEvent(ComponentActivity.java:140)
    at androidx.appcompat.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:569)
    at androidx.appcompat.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:59)
    at androidx.appcompat.app.AppCompatDelegateImpl$AppCompatWindowCallback.dispatchKeyEvent(AppCompatDelegateImpl.java:3054)
    at com.android.internal.policy.DecorView.dispatchKeyEvent(DecorView.java:367)
    at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:5413)
    at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:5281)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4788)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4841)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4807)
    at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4947)
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4815)
    at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:5004)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4788)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4841)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4807)
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4815)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4788)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4841)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4807)
    at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4980)
    at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:5141)
    at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:3064)
    at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:2607)
    at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:2598)
    at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:3041)
    at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:143)
    at android.os.MessageQueue.nativePollOnce(Native Method)
    at android.os.MessageQueue.next(MessageQueue.java:336)
    at android.os.Looper.loop(Looper.java:174)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

Answer 1

等待大神答复