WPF: Where do I get a Threadsafe CollectionView?

Question

When updating a collection of business objects on a background thread I get this error message:

This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread.

Ok, that makes sense. But it also begs the question, what version of CollectionView does support multiple threads and how do I make my objects use it?

Answer 1

None of them, just use Dispatcher.BeginInvoke

Answer 2

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

Answer 3

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.