Avoid duplicated event handlers?

Question

How do I avoid an event from being handled twice (if is the same handler?)

Module Module1
  Sub Main()
    Dim item As New Item
    AddHandler item.TitleChanged, AddressOf Item_TitleChanged
    AddHandler item.TitleChanged, AddressOf Item_TitleChanged

    item.Title = "asdf"

    Stop
  End Sub
  Private Sub Item_TitleChanged(sender As Object, e As EventArgs)
    Console.WriteLine("Title changed!")
  End Sub
End Module

Public Class Item
  Private m_Title As String
  Public Property Title() As String
    Get
      Return m_Title
    End Get
    Set(ByVal value As String)
      m_Title = value
      RaiseEvent TitleChanged(Me, EventArgs.Empty)
    End Set
  End Property

  Public Event TitleChanged As EventHandler
End Class

Output:

Title changed!
Title changed!

Desired output:

Title changed!

I want the event manager to detect that this event is already handled by this handler and so it shouldn't rehandle (or readd) it.

Answer 1

You can also just always call RemoveHandler before AddHandler. I have found this practical in specific scenarios.