Silverlight ListBox with ObservableCollection<T> and dynamic filter

Question

Lets say I have this class:

public class MyData
{
    public bool IsActive{get;set;}
    public String Data1 {get;set;}
    public String Data2 {get;set;}
}

and an

ObservableCollection<MyData> data = new ObservableCollection<MyData>;
ListBox.ItemsSource = data;

Adding items to the ObservableCollectionworks as expected; however, I want to make sure that my listbox only displays items where IsActive is set to 'true' -- I can't use a Linq query to set the ItemsSource because then its not an ObservableCollection, its IEnumerable and does not do any update notifications to the listbox.

Answer 1

Your answer is CollectionViewSource. Instead of binding to the list, bind to an instance of CollectionViewSource.

A slightly degenerate example follows (I am not sure if you're using ViewModels, Locators, etc to resolve your data and your list.)

Assume in your markup you have a CollectionViewSource declared in your resources as follows:

<phone:PhoneApplicationPage.Resources>
    <CollectionViewSource x:Key="src"/>
</phone:PhoneApplicationPage.Resources>

Then your list binding looks like:

<ListBox x:Name="MyListBox" ItemsSource="{Binding Source={StaticResource src}}">

Finally, in code you can marry your list and your collection view source:

        var collectionView = this.Resources["src"] as CollectionViewSource;
        // Check for null, etc.
        collectionView.Source = observableCollectionThatIAmBindingTo;
        collectionView.View.Filter=new Predicate<Object>(o => ((ItemType)o).IsActive );

Additionally, you may want to check out Bea Stollnitz' articles on the topic at:

http://bea.stollnitz.com/blog/?p=31

http://bea.stollnitz.com/blog/?p=392