How do I update an IValueConverter on CollectionChanged?

Question

Here\'s a basic example to explain my problem. Let\'s say I have

ObservableCollection Numbers {get; set;}

and an IValueConverte

Answer 1

This is actually surprisingly very difficult. An IValueConverter doesn't update, so this does not work as you'd hope.

I wrote a sample on the Microsoft Expression Gallery called Collection Aggregator that shows a working, if convoluted, approach to making this work via a Behavior that does the aggregation (Count, in your case, although I also support Sum, Average, etc) for you, instead of a converter.