When Clearing an ObservableCollection, There are No Items in e.OldItems

Question

I have something here that is really catching me off guard.

I have an ObservableCollection of T that is filled with items. I also have an event handler attached to t

Answer 1

Okay, I know this is a very old question but I have come up with a good solution to the issue and thought I would share. This solution takes inspiration from a lot of the great answers here but has the following advantages:

• No need to create a new class and override methods from ObservableCollection
• Does not tamper with the workings of NotifyCollectionChanged (so no messing with Reset)
• Does not make use of reflection

Here is the code:

 public static void Clear(this ObservableCollection collection, Action> unhookAction)
 {
     unhookAction.Invoke(collection);
     collection.Clear();
 }

This extension method simply takes an Action which will be invoked before the collection is cleared.