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Binding to Sorted/Filtered Data

A common UI task that applications need to do is display sorted and/or filtered 'views' of data. In Avalonia this can be accomplished by connecting a SourceCache<TObject, TKey> or a SourceList<T> to a ReadOnlyObservableCollection<T> and binding to that collection

Creating a Source Cache

SourceCache<TObject, TKey> or SourceList<T> come from Dynamic Data in ReactiveUI Example:
// (x => x.Id) property that serves as the unique key for the cache
private SourceCache<TestViewModel, Guid> _sourceCache = new (x => x.Id);
Then the _sourceCache can be populated through the AddOrUpdate method

Creating Sorted Or Filtered Views

Next the ReadOnlyObservableCollection<T> can be bound to the filtered or sorted _sourceCache. The sorting/filtering is done similarly to linq.
private readonly ReadOnlyObservableCollection<TestViewModel> _testViewModels;
public ReadOnlyObservableCollection<TestViewModel> TestViewModels => _testViewModels;
...
public MainWindowViewModel(){
// Populate the source cache via _sourceCache.AddOrUpdate
...
_sourceCache.Connect()
// Sort Ascending on the OrderIndex property
.Sort(SortExpressionComparer<TestViewModel>.Ascending(t => t.OrderIndex))
.Filter(x => x.Id.ToString().EndsWith('1'))
// Bind to our ReadOnlyObservableCollection<T>
.Bind(out _testViewModels)
// Subscribe for changes
.Subscribe();
}

Binding

Now that the _sourceCache is created and populated and the ReadOnlyObservableCollection<T> is created and bound we can go into our view and bind exactly the way we normally would with an ObservableCollection<T>
<Design.DataContext>
<vm:MainWindowViewModel/>
</Design.DataContext>
​
<TreeView Items="{Binding TestViewModels}">
<TreeView.DataTemplates>
!-- DataTemplate Definitions -->
</TreeView.DataTemplates>
</TreeView>