Find Controls in <EditItemTemplate> in GridView web control, ASP.NET 2.0

Hi experts,

I'm have GridView control in my ASP.NET page. Within  <EditItemTemplate> in one of the GridView's columns, there is a Textbox. I'm just wondering, is it possible / how to get a reference of the textbox control so I can do something with it (i.e. When user enter editing mode, set the width of the textbox base on the length of text string)

 I tried the following, but it gives me NullReference exception

Private Sub GridView1_RowEditing(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewEditEventArgs) Handles GridView1.RowEditing
        Dim mytxt As TextBox = Me.GridView1.Rows(e.NewEditIndex).FindControl("txtLastName")
        mytxt.Columns = GridView1.Rows(e.NewEditIndex).Cells(3).Controls.Item(1)      ' This is the text supposed to be  in the textbox
End Sub