Handles vs. AddHandler

Question

Is there an advantage to dynamically attaching/detaching event handlers?

Would manually detaching handlers help ensure that there isn't a reference remaining to a disposed object?

Answer 1

I'm pretty sure that the Handles clause is just syntactic sugar and inserts an AddHandler statement into your constructor. I tested using this code and disabled the application framework so the constructor wouldn't have extra stuff:

Public Class Form1

    Public Sub New()
        ' This call is required by the Windows Form Designer. '
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call. '
        AddHandler Me.Load, AddressOf Form1_Load
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim breakpoint As Integer = 4
    End Sub
End Class

The IL ended up like this:

  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  call       instance void [System.Windows.Forms]System.Windows.Forms.Form::.ctor()
  IL_0007:  nop
  IL_0008:  ldarg.0
  IL_0009:  ldarg.0
  IL_000a:  dup
  IL_000b:  ldvirtftn  instance void WindowsApplication1.Form1::Form1_Load(object,
                                                                           class [mscorlib]System.EventArgs)
  IL_0011:  newobj     instance void [mscorlib]System.EventHandler::.ctor(object,
                                                                          native int)
  IL_0016:  call       instance void [System.Windows.Forms]System.Windows.Forms.Form::add_Load(class [mscorlib]System.EventHandler)

 '... lots of lines here '

  IL_0047:  ldarg.0
  IL_0048:  callvirt   instance void WindowsApplication1.Form1::InitializeComponent()
  IL_004d:  nop
  IL_004e:  ldarg.0
  IL_004f:  ldarg.0
  IL_0050:  dup
  IL_0051:  ldvirtftn  instance void WindowsApplication1.Form1::Form1_Load(object,
                                                                           class [mscorlib]System.EventArgs)
  IL_0057:  newobj     instance void [mscorlib]System.EventHandler::.ctor(object,
                                                                          native int)
  IL_005c:  callvirt   instance void [System.Windows.Forms]System.Windows.Forms.Form::add_Load(class [mscorlib]System.EventHandler)
  IL_0061:  nop
  IL_0062:  nop
  IL_0063:  ret
} // end of method Form1::.ctor

Notice two identical blocks of code around IL_000b and IL_0051. I think it's just syntactic sugar.