Can not operate ObservableCollection in multi threads

Question

It seems the ObservableCollection only support add, remove, clear operation from the UI thread, It throw Not Support Exception if it is operated by a NO UI thread. I tried t

Answer 1

You might want to investigate my answer to this perhaps -but please note that the code came from here and cannot be credited to me. Though I tried to implement it in VB. : Original Site

I've used this to populate a WPF listbox from a class that has an ObservableCollectionEx populated asynchronously from an access database. It does work.

public class ObservableCollectionEx : ObservableCollection
{
   // Override the event so this class can access it
   public override event System.Collections.Specialized.NotifyCollectionChangedEventHandler    
 CollectionChanged;

   protected override void OnCollectionChanged    (System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
   {
  // Be nice - use BlockReentrancy like MSDN said
  using (BlockReentrancy())
  {
     System.Collections.Specialized.NotifyCollectionChangedEventHandler eventHandler = CollectionChanged;
     if (eventHandler == null)
        return;

     Delegate[] delegates = eventHandler.GetInvocationList();
     // Walk thru invocation list
     foreach (System.Collections.Specialized.NotifyCollectionChangedEventHandler handler in delegates)
     {
        DispatcherObject dispatcherObject = handler.Target as DispatcherObject;
        // If the subscriber is a DispatcherObject and different thread
        if (dispatcherObject != null && dispatcherObject.CheckAccess() == false)
        {
           // Invoke handler in the target dispatcher's thread
           dispatcherObject.Dispatcher.Invoke(DispatcherPriority.DataBind, handler, this, e);
        }
        else // Execute handler as is
           handler(this, e);
     }
  }
}
}