XAML Binding to a CollectionViewSource property on a ViewModel

Question

I have a simple ViewModel like:

public class MainViewModel {
    ObservableCollection<Project> _projects;
    public MainViewModel() {
        // Fill _projects from DB here...
        ProjectList.Source = _projects;
        ProjectList.Filter = ...;
    }

    public CollectionViewSource ProjectList { get; set; }
}

I set the window's DataContext to a new instance of that ViewModel in the constructor:

public MainWindow() {
    this.DataContext = new MainViewModel();
}

Then in the Xaml I am attempting to bind the ItemsSource of a ListBox to that ProjectList property.

Binding just ItemsSource like so doesn't work:

<ListBox ItemsSource="{Binding ProjectList}" ItemTemplate="..." />

But if I first rebase the DataContext this works:

<ListBox DataContext="{Binding ProjectList}" ItemsSource="{Binding}" ItemTemplate="..." />

Shouldn't the first method work properly? What might I be doing wrong?

Jasmin

Are you getting your data from the DB synchronously or asynchronously ? – Peppermint

synchronously, beside if it was a race condition then the second method would not work either... – Jasmin

Answer 1

If you are using CollectionViewSource you need to bind ItemsSource to ProjectList.View instead of ProjectList. That should solve your problem.

Workable

So I guess I can't duplicate my problem like that either... I've updated the question with what the ViewModel "really" looks like. – Jasmin

See my updated answer. I'm not exactly sure why CollectionViewSource works this way, but its the way I've always had to work with them. – Workable

Thank you, that's very helpful. This is the first time I've used a CollectionViewSource. I ended up making the property type ICollectionView and in the getter I return the View property from a private CollectionViewSource. That way I don't need to worry about binding to .View which would break if I change the collection type of that ViewModel property in the future. – Jasmin

Answer 2

From what you provided the first method should perfectly work. Devil lurks somewhere in details.

PS: Maybe you didn't specify implementation of INotifyPropertyChanged interface in sake of post size, but be careful in production. It's very easy to get a memory leak if you don't implement it.

Dyna

Yes, it actually does implement that interface. Call it a test case if you will. – Jasmin