[Feature]Implement ICollectionView.CollectionGroups in AdvancedCollectionView

[ianier]

It would be great for AdvancedCollectionView to implement ICollectionView.CollectionGroups, based on item's IGrouping, just like the default view implementation of CollectionViewSource does.

This would allow using groping and incremental loading together, which CollectionViewSource doesn't support.

Currently I'm working on inheriting from AdvancedCollectionView and redefining CollectionGroups, to see how far I can go with this scenario.

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This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

[skendrot]

@ianier Have you been able to investigate this addition?

[ianier]

I finally inherited from IncrementalLoadingCollection and implemented ICollectionViewFactory.CreateView() to do my own grouping (ICollectionView.CollectionGroups), inheriting from AdvancedCollectionView. Grouping is done with a simple delegate, which proved easier to do than my original idea.
At the moment I don't have time to work on a PR, but here's the code of my collection view in cased someone wants to have a look:

public class AdvancedCollectionViewEx : AdvancedCollectionView, ICollectionView
{
    private class CollectionViewGroup : ICollectionViewGroup
    {
        public ObservableVector<object> Items { get; }

        public object Group { get; }

        public IObservableVector<object> GroupItems => Items;

        public CollectionViewGroup(object group)
        {
            Group = group;
            Items = new ObservableVector<object>();
        }
    }

    public Func<object, object> Group { get; }

    private ObservableVector<object> _collectionGroups;

    // The CollectionGroups property is of type IObservableVector;, but these objects should implement ICollectionViewGroup.
    IObservableVector<object> ICollectionView.CollectionGroups
    {
        get { return _collectionGroups; }
    }

    public AdvancedCollectionViewEx(IList source, Func<object, object> group) : base(source)
    {
        if (group != null)
        {
            Group = group;
            _collectionGroups = new ObservableVector<object>();
            RebuildGroups();
            VectorChanged += HandleViewChanges;
        }
    }

    private void RebuildGroups()
    {
        _collectionGroups.IsVectorChangedDeferred = true;
        try
        {
            _collectionGroups.Clear();

            if (Source != null)
            {
                foreach (var item in Source)
                {
                    AddGroupedItem(item);
                }
            }
        }
        finally
        {
            // trigger any changes for children
            foreach (CollectionViewGroup col in _collectionGroups)
            {
                col.Items.IsVectorChangedDeferred = false;
            }
            // then trigger any changes for self
            _collectionGroups.IsVectorChangedDeferred = false;
        }
    }

    private void AddGroupedItem(object item)
    {
        // classify the item
        object key = GetItemGroup(item);
        // find the group the item belongs to
        var col = _collectionGroups.Cast<CollectionViewGroup>().FirstOrDefault(g => Comparer.Default.Compare(g.Group, key) == 0);
        // if not found, create the item
        if (col == null)
        {
            col = new CollectionViewGroup(key);
            _collectionGroups.Add(col);
        }
        // propagate change deferral
        col.Items.IsVectorChangedDeferred = _collectionGroups.IsVectorChangedDeferred;
        // add the item to the collection
        col.GroupItems.Add(item);
    }

    private void RemoveGroupedItem(object item)
    {
        foreach (CollectionViewGroup g in _collectionGroups)
        {
            // propagate change deferral
            g.Items.IsVectorChangedDeferred = _collectionGroups.IsVectorChangedDeferred;
            // actually remove the item
            g.Items.Remove(item);
        }
    }

    private object GetItemGroup(object item)
    {
        return Group?.Invoke(item);
    }

    private void HandleViewChanges(IObservableVector<object> sender, IVectorChangedEventArgs args)
    {
        int ndx = (int)args.Index;
        switch (args.CollectionChange)
        {
            case CollectionChange.ItemChanged:
                RemoveGroupedItem(this[ndx]);
                AddGroupedItem(this[ndx]);
                break;
            case CollectionChange.ItemInserted:
                AddGroupedItem(this[ndx]);
                break;
            case CollectionChange.ItemRemoved:
                RebuildGroups();
                break;
            case CollectionChange.Reset:
                RebuildGroups();
                break;
        }
    }
}

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.

This issue has been marked as "needs attention 👋" due to no activity for 15 days. Please triage the issue so the fix can be established.