IssueTracker

Component used: Paging Library
Version used: 1.0.0-alpha2
Devices/Android versions reproduced on:
Android O
Unit tests in Android studio

- Sample project to trigger the issue.
- A screenrecord or screenshots showing the issue (if UI related).

We are seeing crashes with the following stack trace:
10-03 09:42:42.633 26917 26917 E AndroidRuntime: FATAL EXCEPTION: main
10-03 09:42:42.633 26917 26917 E AndroidRuntime: Process: com.app.name, PID: 26917
10-03 09:42:42.633 26917 26917 E AndroidRuntime: java.lang.IndexOutOfBoundsException: Inconsistency detected. Invalid view holder adapter positionViewHolder{d08cbcb position=84 id=-1, oldPos=75, pLpos:55 scrap [attachedScrap] tmpDetached no parent} android.support.v7.widget.RecyclerView{804e943 VFED..... ......ID 0,0-1080,795 #7f080071 app:id/group_feed_recycler_view}, adapter:com.app.name.ui.main.GroupFeedRowAdapter@5fbebc0, layout:android.support.v7.widget.LinearLayoutManager@49810f9, context:com.app.name.ui.main.MainActivity@cf99efb
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView$Recycler.validateViewHolderForOffsetPosition(RecyclerView.java:5421)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5603)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5563)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5559)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2229)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1556)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1516)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:618)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3644)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3408)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1710)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.support.v7.widget.RecyclerView$ViewFlinger.run(RecyclerView.java:4806)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.view.Choreographer.doCallbacks(Choreographer.java:723)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.view.Choreographer.doFrame(Choreographer.java:655)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.os.Handler.handleCallback(Handler.java:789)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:98)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.os.Looper.loop(Looper.java:164)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:6541)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
10-03 09:42:42.633 26917 26917 E AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

We also see the same issue when running unit tests using the instant run rule:
@Rule
public TestRule instantRunRule = new InstantTaskExecutorRule();

We think the problem is that the adapter is calling notifyItemRangeInserted before updating the list the adapter is using.
We are currently using a workaround in our code to try and provide the correct list when the adapter is asked for it:

private List<Item> mListSnapshot;
private PagedList<Item> mList;

public void setList(PagedList<Item> list)
{
    mList = list;
    mListSnapshot = list.snapshot();
    super.setList(list);
}

public int getItemCount()
{
    if (mList != super.getCurrentList())
    {
        // The adapter is calculating a diff
        return (mListSnapshot == null) ? 0 : mListSnapshot.size();
    }
    return (mList == null) ? 0 : mList.size();
}

public Item getItem(int index)
{
    if (mList != super.getCurrentList())
    {
        if (mListSnapshot == null)
        {
            throw new IndexOutOfBoundsException("Item count is zero, getItem() call is invalid");
        }

        // No loadAround as the snapshot is not a paged list
        return mListSnapshot.get(index);
    }
    else
    {
        if (mList == null)
        {
            throw new IndexOutOfBoundsException("Item count is zero, getItem() call is invalid");
        }

        mList.loadAround(index);
        return mList.get(index);
    }
}

This code means that the values from the snapshot of the list are returned when notifyItemRangeInserted is called after calculating the diff (rather than the old list). The snapshot is used as that is what the diff was calculated against.

Can you tell me if there is a specific reason the default adapter calls notifyItemRangeInserted before updating the list, and if there are any big problems that may be encountered using the above workaround?