Question

The CollectionViewSource.GetDefaultView() method is not in Silverlight 3. In WPF I have this extension method:

public static void SetActiveViewModel<ViewModelType>(this ViewModelBase viewModel,
    ViewModelType collectionItem,
    ObservableCollection<ViewModelType> collection) where ViewModelType : ViewModelBase
{
    Debug.Assert(collection.Contains(collectionItem));
    ICollectionView collectionView = CollectionViewSource.GetDefaultView(collection);
    if(collectionView != null) collectionView.MoveCurrentTo(collectionItem);
}

How can this be written in Silverlight 3?

Answer 1

Silverlight does not contain the concept of a Default view. When you ask a control in Silverlight to bind to a collection it really does bind to the collection, it does not bind to a default view.

As result I don’t think there can be a direct and complete port of your extension method. Some re-engineering of your MVVM implementation will be needed. I’ve not come across the concept of a collection of view model instances before so I’m not exactly sure what would be appropriate in your case.

A couple of approaches I’ve seen with CollectionViewSource is to either have the CollectionViewSource defined in the Xaml and bind its Source to something in the ViewModel. Alternatively have a ViewModel expose a CollectionViewSource property and have the View xaml bind to its View proeprty.