VB.Net Tutorial/Event/AddressOf

AddHandler and AddressOf

<source lang="vbnet">Option Strict On imports System imports System.Drawing imports System.Windows.Forms public class MouseEnterHoverLeave : inherits Form

 private btn as Button
 public sub New()
   Size = new Size(400,400)
   btn = new Button()
   btn.Parent = me
   btn.Location = new Point(50,50)
   btn.Size = new Size(150,25)
   AddHandler btn.MouseEnter, AddressOf btn_MouseEnter
   AddHandler btn.MouseHover, AddressOf btn_MouseHover
   AddHandler btn.MouseLeave, AddressOf btn_MouseLeave
 end sub
 public shared sub Main() 
   Application.Run(new MouseEnterHoverLeave())
 end sub
 private sub btn_MouseEnter(ByVal sender as object,ByVal e as EventArgs)
   btn.Text = "MouseEnter"
   Console.WriteLine("Button MouseEnter")
 end sub
 private sub btn_MouseHover(ByVal sender as object,ByVal e as EventArgs)
   btn.Text = "MouseHover"
   Console.WriteLine("Button MouseHover")
 end sub
 private sub btn_MouseLeave(ByVal sender as object,ByVal e as EventArgs)
   btn.Text = "MouseLeave"
   Console.WriteLine("Button MouseLeave")
 end sub
 protected overrides sub OnMouseEnter(ByVal e as EventArgs)
   myBase.OnMouseEnter(e)
   Console.WriteLine("Form MouseEnter")
 end sub
 protected overrides sub OnMouseHover(ByVal e as EventArgs)
   myBase.OnMouseHover(e)
   Console.WriteLine("Form MouseHover")
 end sub
 protected overrides sub OnMouseLeave(ByVal e as EventArgs)
   myBase.OnMouseLeave(e)
   Console.WriteLine("Form MouseLeave")
 end sub

end class</source>

AddressOf operator

<source lang="vbnet">Module Module1

   Delegate Sub GreetingMethod()
   Dim Greeting As New GreetingMethod(AddressOf MorningEnglish)
   Sub MorningEnglish()
       Console.WriteLine("Good morning")
   End Sub
   Sub AfternoonEnglish()
       Console.WriteLine("Good afternoon")
   End Sub
   Sub EveningEnglish()
       Console.WriteLine("Good evening")
   End Sub
   Sub MorningSpanish()
       Console.WriteLine("Buenas dias")
   End Sub
   Sub AfternoonSpanish()
       Console.WriteLine("Buenos tardes")
   End Sub
   Sub EveningSpanish()
       Console.WriteLine("Buenos noches")
   End Sub
   Sub Main()
       Greeting = AddressOf MorningEnglish
       Greeting = AddressOf AfternoonEnglish
       Greeting = AddressOf EveningEnglish
       Greeting = AddressOf MorningSpanish
       Greeting = AddressOf AfternoonSpanish
       Greeting = AddressOf EveningSpanish
       Greeting.Invoke()
   End Sub

End Module</source>

Buenos noches

Use EventHandler with AddressOf

<source lang="vbnet">Module Module1

 Sub AHandler(ByVal o As Object, ByVal e As System.EventArgs)
   Console.WriteLine("handler")
 End Sub

 Sub Main()
   Dim TodayDate As DateTime = Today()
   Console.WriteLine(TodayDate)
   Dim MyArray() As Double = {3.159, System.Math.Sqrt(2)}
   Console.WriteLine(MyArray(1))
   Dim MyHandler As EventHandler " = AddressOf AHandler
   MyHandler(Nothing, Nothing)
   Try
     Dim MyException As Exception = New Exception("Raise an exception!")
     Throw MyException
   Catch e As Exception
     Console.WriteLine(e.StackTrace())
   End Try
 End Sub

End Module</source>

11/05/2007 12:00:00 AM
1.4142135623731
Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an ob
ject.
   at Module1.Main()