Unexpected problem when unmounting

[wellguimaraes]

I've got this error reported from an app in production and it seems that it tried to remove view more than once. Maybe a simple try/catch on L138 would solve with no side effects.

Fatal Exception: java.lang.IllegalArgumentException
The observer is null.

android.database.Observable.unregisterObserver (Observable.java:64)
android.widget.BaseAdapter.unregisterDataSetObserver (BaseAdapter.java:42)
android.widget.AbsListView.onDetachedFromWindow (AbsListView.java:2668)
android.view.View.dispatchDetachedFromWindow (View.java:12024)
android.view.ViewGroup.dispatchDetachedFromWindow (ViewGroup.java:2612)
android.view.ViewGroup.dispatchDetachedFromWindow (ViewGroup.java:2610)
android.view.ViewGroup.removeViewsInternal (ViewGroup.java:3792)
android.view.ViewGroup.removeViews (ViewGroup.java:3674)
trikita.anvil.Anvil.unmount (Anvil.java:138)

[helgoboss]

I have a very similar Anvil issue after switching from Android SDK 23 to 25. When unmounting a RecyclerView, a NullPointerException is thrown. Because the RecyclerView was already detached from the window once and Anvil tries to detach it again.

First stack trace:

at android.support.v7.widget.RecyclerView.onDetachedFromWindow(RecyclerView.java:2479)
at android.view.View.dispatchDetachedFromWindow(View.java:14573)
at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3073)
at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3065)
at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3065)
at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4605)
at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4578)
at android.view.ViewGroup.removeView(ViewGroup.java:4509)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1406)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1523)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1598)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2145)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2092)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1998)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:709)
at android.os.Handler.handleCallback(Handler.java:745)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:171)
at android.app.ActivityThread.main(ActivityThread.java:5454)
at java.lang.reflect.Method.invoke(Method.java:-1)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Second stack trace (causing the exception):

  at android.support.v7.widget.RecyclerView.onDetachedFromWindow(RecyclerView.java:2479)
  at android.view.View.dispatchDetachedFromWindow(View.java:14573)
  at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3073)
  at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3065)
  at android.view.ViewGroup.removeViewsInternal(ViewGroup.java:4706)
  at android.view.ViewGroup.removeViews(ViewGroup.java:4570)
  at trikita.anvil.Anvil.unmount(Anvil.java:138)
  at trikita.anvil.RenderableView.onDetachedFromWindow(RenderableView.java:33)
  at android.view.View.dispatchDetachedFromWindow(View.java:14573)
  at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3073)
  at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4605)
  at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4578)
  at android.view.ViewGroup.removeView(ViewGroup.java:4509)
  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1406)
  at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1523)
  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1598)
  at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2145)
  at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2092)
  at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1998)
  at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:709)
  at android.os.Handler.handleCallback(Handler.java:745)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at android.os.Looper.loop(Looper.java:171)
  at android.app.ActivityThread.main(ActivityThread.java:5454)
  at java.lang.reflect.Method.invoke(Method.java:-1)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Seems like Android itself takes care of removing the Anvil views and Anvil tries to do it a second time. Not sure what would be the cleanest solution here.