Proposal: allow incremental loading for grouped collections

[FrayxRulez]

Proposal: allow incremental loading for grouped collections

Currently CollectionViewSource will ignore ISupportIncrementalLoading interface if the item source is a grouped list. Even implementing the behavior would lead into catastrophic failures at runtime (Not sure if this is still the case, actually, but it was last time I tried).
Developers usually have to end up with (not really optimal) workaround solutions, such as feeding the ListView with a ObservableCollection<object> collection and including group headers directly in it, having to deal with ItemTemplateSelectors, ItemContainerStyleSelectors, and so on, and other stuff, such multiple/single selection handling. This would also end up with a lot of compromises in terms of UI, as in the following example, that are kind of confusing for the users:

Summary

ISupportIncrementalLoading interface should be supported by grouped CollectionViewSource and ListView.

Rationale

• Lists grouped by date and retrieved by a remote endpoint need this.
• Current possibilities require too many workarounds.
• Migrating to ItemsRepeater would require too much work in many scenarios (Especially as it doesn't support incremental loading as well).

Scope

Capability	Priority
This proposal will allow developers to implement incremental loading in grouped CollectionViewSources	Must

Important Notes

Open Questions

[anawishnoff]

@FrayxRulez, thanks for submitting this. My apologies that it's taken so long to get a reply!

@ranjeshj is there a reason that grouped CollectionViewSources don't allow for incremental loading?

[Difegue]

In a similar fashion, CollectionViewSources don't implement IItemsRangeInfo, which is classically used in random access data virtualization.

Both ISupportIncrementalLoading and IItemsRangeInfo are usually the go-tos for data virtualization in ListViews, and they're rather hard to use in grouped collections without workarounds as mentioned.

I stumbled into this problem today, but some digging reveals it's been a pain point with WinRT dev for a while:
https://stackoverflow.com/questions/14186478/how-to-style-groups-of-data-as-they-are-loaded-incrementally-in-winrt
microsoft/Windows-universal-samples#803
https://stackoverflow.com/questions/34705422/does-iitemsrangeinfo-support-collectionviewsource
https://stackoverflow.com/questions/60317701/implement-deferred-item-loading-in-a-grouped-icollectionview

[ranjeshj]

Both ISupportIncrementalLoading and IItemsRangeInfo seem targeted towards flat collections, not collection of collections, so I'm not entirely sure how these map in grouped cases. @MikeHillberg any ideas ?