List goes blank after reset event

[nielsenko]

When an item source raises a CollectionChanged event with action NotifyCollectionChangedAction.Reset, then _dataSource is simply cleared.

case NotifyCollectionChangedAction.Reset:
  _dataSource.Clear();
  parentView.GetRecycledViewPool().Clear();
  NotifyDataSetChanged();
  break;

Hence the list view goes blank, instead of actually re-evaluating the ItemsSource, at least for me.

Platform used during testing

• OS: Android
• Device: Nexus 5x, Honeywell EDA51
• Sdk version: Android SDK 21+
• Xamarin.Forms: 4.1.0-sr3

[roubachof]

I don't think I will support the semantic you gave about the Reset action (re-evaluating vs clearing), because:

1. ObservableCollection only sends Reset action when the collection has been cleared.

protected override void ClearItems()
    {
      this.CheckReentrancy();
      base.ClearItems();
      this.OnCountPropertyChanged();
      this.OnIndexerPropertyChanged();
      this.OnCollectionReset();
    }

2. Offical doc

Reset	4	The content of the collection was cleared.

If your ItemsSource changed a lot, just raise the property changed from your view model, and the view source / recycler adapter will be refreshed.

[nielsenko]

I think this actually changed with .NET 4.5. I'm old enough to remember different semantics for Reset, aka lots has happened, please re-evaluate your binding :-)

Anyway, fx DynamicData.Binding.ObservableCollectionExtended will simply raise a Reset after notification has been suspended. Similar using DynamicData.IObservable<IChangeSet<T>>.Bind has a resetThreshold argument (that defaults to 25) for how many changes to track before simply raising a reset event, instead of creating an storm of Adds, Removes etc. So to play nice with DynamicData you might consider to reconsider? I would love to be able to use it together with Sharpnado.

[nielsenko]

I tried using your suggested workaround, ie. raising a PropertyChanged event on the property that ItemsSource is bound to, just after the CollectionChanged Reset event, but the control stays blank :-/

[roubachof]

Ok you won :)
Since the old semantic is backward compatible with the new one.

[nielsenko]

🙏 Thank you. Do you have a target date for your next release? No promises, just a vague idea?

[roubachof]

It will be published in September.

[roubachof]

fixed in v1.3.0