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 ItemsSource="{Binding TestViewModels}">
    <TreeView.DataTemplates>
        !-- DataTemplate Definitions -->
    </TreeView.DataTemplates> 
</TreeView>