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

I was just going through some of the charting code in the Silverlight and WPF toolkits and noticed that they also solved this problem (in a kind of similar way) ... and I thought I would go ahead and post their solution.

Basically, they also created a derived ObservableCollection and overrode ClearItems, calling Remove on each item being cleared.

Here is the code:

/// 

/// An observable collection that cannot be reset.  When clear is called
/// items are removed individually, giving listeners the chance to detect
/// each remove event and perform operations such as unhooking event 
/// handlers.
/// 
/// The type of item in the collection.
public class NoResetObservableCollection : ObservableCollection
{
    public NoResetObservableCollection()
    {
    }

    /// 

    /// Clears all items in the collection by removing them individually.
    /// 
    protected override void ClearItems()
    {
        IList items = new List(this);
        foreach (T item in items)
        {
            Remove(item);
        }
    }
}