Final app (network + database) crashes when scrolling up and down (a lot)

[ianribas]

I'm not sure this is the right place for this issue, but I think it's where it will be clearer to explain.

I first noticed this when navigating on the app after I finished the code lab, but the stack trace below comes from the app generated with the step13-19_network_and_database branch.

Environment:

• Android Studio 4.1.0-alpha10, AGP 4.1.0-beta01, Gradle 6.5-rc-1
• Device: Samsung Galaxy S8, Android 7.0 (API 24)
• Emulator: Pixel 3a, Android 10 (API 29)

Steps to reproduce:

• Run app
• Fling the list down many times
• If still not happening, fling up a few times and then back down.

I also noticed that the list will sometimes scroll to the top when updating from the database while flinging down.

And also, when the error below happens, position is 0.

25609-25609/com.example.android.codelabs.paging E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.android.codelabs.paging, PID: 25609
    java.lang.UnsupportedOperationException: Unknown view
        at com.example.android.codelabs.paging.ui.ReposAdapter.getItemViewType(ReposAdapter.kt:42)
        at androidx.recyclerview.widget.NestedAdapterWrapper.getItemViewType(NestedAdapterWrapper.java:146)
        at androidx.recyclerview.widget.MergeAdapterController.getItemViewType(MergeAdapterController.java:318)
        at androidx.recyclerview.widget.MergeAdapter.getItemViewType(MergeAdapter.java:174)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6283)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6216)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6212)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2314)
        at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
        at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
        at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4215)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3926)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4484)
        at android.view.View.layout(View.java:18874)
        at android.view.ViewGroup.layout(ViewGroup.java:5954)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
        at android.view.View.layout(View.java:18874)
        at android.view.ViewGroup.layout(ViewGroup.java:5954)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:18874)
        at android.view.ViewGroup.layout(ViewGroup.java:5954)
        at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:446)
        at android.view.View.layout(View.java:18874)
        at android.view.ViewGroup.layout(ViewGroup.java:5954)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:18874)
        at android.view.ViewGroup.layout(ViewGroup.java:5954)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
        at android.view.View.layout(View.java:18874)
        at android.view.ViewGroup.layout(ViewGroup.java:5954)
        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:935)
        at android.view.View.layout(View.java:18874)
        at android.view.ViewGroup.layout(ViewGroup.java:5954)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2697)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2413)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1550)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7189)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:959)
        at android.view.Choreographer.doCallbacks(Choreographer.java:734)
        at android.view.Choreographer.doFrame(Choreographer.java:670)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:945)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6776)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

[solamour]

If you comment out the following line, you should at least be able to prevent the crash.

app\src\main\java\com\example\android\codelabs\paging\ui\SearchRepositoriesActivity.kt
    ...
    lifecycleScope.launch {
        @OptIn(ExperimentalPagingApi::class)
        adapter.dataRefreshFlow.collect {
            binding.list.scrollToPosition(0)    <-- This causes crash.
        }
    }

(I think) the idea is to scroll to the top whenever the search term changes (https://codelabs.developers.google.com/codelabs/android-paging/#8), but depending on what's in the list at the moment you scroll through, ReposAdapter might incorrectly try to draw something that doesn't exist yet.

[tunjid]

@ianribas I believe this should no longer be an issue with the latest version of the codelab.