How do I update an ObservableCollection via a worker thread?

Question

I\'ve got an ObservableCollection a_collection; The collection contains \'n\' items. Each item A looks like this:

public class A : INot         


        

Answer 1

Technically the problem is not that you are updating the ObservableCollection from a background thread. The problem is that when you do so, the collection raises its CollectionChanged event on the same thread that caused the change - which means controls are being updated from a background thread.

In order to populate a collection from a background thread while controls are bound to it, you'd probably have to create your own collection type from scratch in order to address this. There is a simpler option that may work out for you though.

Post the Add calls onto the UI thread.

public static void AddOnUI(this ICollection collection, T item) {
    Action addMethod = collection.Add;
    Application.Current.Dispatcher.BeginInvoke( addMethod, item );
}

...

b_subcollection.AddOnUI(new B());

This method will return immediately (before the item is actually added to the collection) then on the UI thread, the item will be added to the collection and everyone should be happy.

The reality, however, is that this solution will likely bog down under heavy load because of all the cross-thread activity. A more efficient solution would batch up a bunch of items and post them to the UI thread periodically so that you're not calling across threads for each item.

The BackgroundWorker class implements a pattern that allows you to report progress via its ReportProgress method during a background operation. The progress is reported on the UI thread via the ProgressChanged event. This may be another option for you.