.NET Framework 4.6 and 4.5
When overridden in a derived class, performs additional work before the Insert or Add method adds an item to the collection.
protected virtual void OnInsert(
Collections derived from StateManagedCollection can override the OnInsert method to perform any additional work before an item is added to the collection using the Add or Insert method.
Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0