Custom Event - invokation list implementation considerations
- by M.A. Hanin
I'm looking for some pointers on implementing Custom Events in VB.NET (Visual Studio 2008, .NET 3.5).
I know that "regular" (non-custom) Events are actually Delegates, so I was thinking of using Delegates when implementing a Custom Event. On the other hand, Andrew Troelsen's "Pro VB 2008 and the .NET 3.5 Platform" book uses Collection types in all his Custom Events examples, and Microsoft's sample codes match that line of thought.
So my question is: what considerations should I have when choosing one design over the other? What are the pros and cons for each design? Which of these resembles the inner-implementation of "regular" events?
Below is a sample code demonstrating the two designs.
Public Class SomeClass
Private _SomeEventListeners As EventHandler
Public Custom Event SomeEvent As EventHandler
AddHandler(ByVal value As EventHandler)
_SomeEventListeners = [Delegate].Combine(_SomeEventListeners, value)
End AddHandler
RemoveHandler(ByVal value As EventHandler)
_SomeEventListeners = [Delegate].Remove(_SomeEventListeners, value)
End RemoveHandler
RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
_SomeEventListeners.Invoke(sender, e)
End RaiseEvent
End Event
Private _OtherEventListeners As New List(Of EventHandler)
Public Custom Event OtherEvent As EventHandler
AddHandler(ByVal value As EventHandler)
_OtherEventListeners.Add(value)
End AddHandler
RemoveHandler(ByVal value As EventHandler)
_OtherEventListeners.Remove(value)
End RemoveHandler
RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
For Each handler In _OtherEventListeners
handler(sender, e)
Next
End RaiseEvent
End Event
End Class
