Question

Say, I have an ObservableCollection

Class Person
  Name
  Event DidSomething

Class House
  WithEvents People as ObservableCollection(of Person)

  Sub OnPersonDidSomething(p as Person)
    Console.WriteLine("{0} did something", p.Name)

Now, how I should implement the handler of this ObservableCollection?

Private Sub People_CollectionChanged( _ 
  sender As Object, _ 
  e As NotifyCollectionChangedEventArgs) Handles People.CollectionChanged

Select Case e.Action
  Case Specialized.NotifyCollectionChangedAction.Add
    For Each mp As Person In e.NewItems
      RemoveHandler mp.DidSomething, AddressOf OnPersonDidSomething
      AddHandler mp.DidSomething, AddressOf OnPersonDidSomething
    Next mp

  Case Specialized.NotifyCollectionChangedAction.Remove
    For Each mp As Person In e.NewItems
      RemoveHandler mp.DidSomething, AddressOf OnPersonDidSomething
    Next mp
End Select

End Sub

Is it correct? What to to for the Move, Replace, Reset actions?

Answer 1

That is correct.

For Replace, you should remove handlers from the old items and add them to the new items.

For Reset, you should panic, because you cannot know which items were removed or added.