RE: AddHandler

From: Iouri Simernitski (iouris_at_micro.nospam.soft.com)
Date: 06/01/04 

Date: Tue, 01 Jun 2004 21:20:45 GMT

Great question!

First of all, make sure that you keep a reference to your text boxes as
long as you need your event handler to run.
If you only use a local variable to hold a reference to the text box, your
handler will stop to work after the garbage collector sweeps it away.
Having just one member variable for all the textboxes would not work other.
Store them in an ArrayList.

Now, back to your question. Indeed, the handler for the Change event does
not have the sender parameter.
You can work around this limitation by creating a helper class that holds a
reference to the textbox.
Here's the code snippet (I used a Word project, but Excel is nearly
identical) :

-------------
   
   Private keepAlive As New System.Collections.ArrayList

   ' Called when the document is opened.
    Private Sub ThisDocument_Open() Handles ThisDocument.Open
    ' Stuff here ..........
      Dim tBox As MSForms.TextBox

      tBox = FindControl("TextBox1")
      ' keep a reference to the control to
      ' prevent garbage collection
      keepAlive.Add(tBox)

      'Instead of 'AddHandler tBox.Change, AddressOf ChangeHandler
      AddHandler tBox.Change, New DelegateHelper(tBox).ChangeDelegate
  End sub
End Class

----------------------------
' Helper class

Public Class DelegateHelper
   Public WithEvents sender As MSForms.TextBox

   Friend ReadOnly Property ChangeDelegate() As
MSForms.MdcTextEvents_ChangeEventHandler
      Get
         Return New MSForms.MdcTextEvents_ChangeEventHandler(AddressOf
OnChange)
      End Get
   End Property

   Friend Sub New(ByVal sender As MSForms.TextBox)
      Me.sender = sender
   End Sub

   Private Sub OnChange()
      ' do stuff
      ' MsgBox(Me.sender.Text)
   End Sub

End Class

---------------
Hope this helps,
iouri
 ----------
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