Adding to an ObservableCollection from a background thread

One annoying thing about ObservableCollection<T> is that it doesn’t support modifications from background threads. That is to say, the CollectionChanged notification doesn’t marshal to the proper thread when it is raised and it causes the exception “This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread”.

I ran into this problem a while back and searched out to see if someone else had solved it. I found a solution from Tamir Khason (a fellow WPF disciple), he wrote a thread-safe version, but I didn’t want to add the locking into the collection itself (I want to manage it at a higher level myself). Really, all I want is to do the notification on the proper (Dispatcher) thread.

It turns out to be pretty easy, here’s my solution:

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);  
            }  
        }
    }
}