I believe What you’re looking for is already part of the API in the ObservableCollection(T) class. Example:
ObservableCollection<int> myList = new ObservableCollection<int>();
myList.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(
delegate(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
{
MessageBox.Show("Added value");
}
}
);
myList.Add(1);