Where do I get a thread-safe CollectionView?

Use:

System.Windows.Application.Current.Dispatcher.Invoke(
    System.Windows.Threading.DispatcherPriority.Normal,
    (Action)delegate() 
    {
         // Your Action Code
    });

This post by Bea Stollnitz explains that error message and why it's worded the way it is.

EDIT: From Bea's blog

Unfortunately, this code results in an exception: “NotSupportedException – This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread.” I understand this error message leads people to think that, if the CollectionView they’re using doesn’t support cross-thread changes, then they have to find the one that does. Well, this error message is a little misleading: none of the CollectionViews we provide out of the box supports cross-thread collection changes. And no, unfortunately we can not fix the error message at this point, we are very much locked down.

Found one.

public class MTObservableCollection<T> : ObservableCollection<T>
{
   public override event NotifyCollectionChangedEventHandler CollectionChanged;
   protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   {
      var eh = CollectionChanged;
      if (eh != null)
      {
         Dispatcher dispatcher = (from NotifyCollectionChangedEventHandler nh in eh.GetInvocationList()
                 let dpo = nh.Target as DispatcherObject
                 where dpo != null
                 select dpo.Dispatcher).FirstOrDefault();

        if (dispatcher != null && dispatcher.CheckAccess() == false)
        {
           dispatcher.Invoke(DispatcherPriority.DataBind, (Action)(() => OnCollectionChanged(e)));
        }
        else
        {
           foreach (NotifyCollectionChangedEventHandler nh in eh.GetInvocationList())
              nh.Invoke(this, e);
        }
     }
  }
}

http://www.julmar.com/blog/mark/2009/04/01/AddingToAnObservableCollectionFromABackgroundThread.aspx

You can get wpf to manage cross thread changes to a collection by enabling collection synchronization like so:

BindingOperations.EnableCollectionSynchronization(collection, syncLock);
listBox.ItemsSource = collection;

This tells WPF that the collection may be modified off the UI thread so it knows it has to marshal any UI changes back to the appropriate thread.

There is also an overload to provide a synchronization callback if you don't have a lock object.

None of them, just use Dispatcher.BeginInvoke