Question

We currently have all of our tracking / analytic code in a usercontrol (ascx). We like this because, using our CMS, we can just drop the control on any page that needs tracking.

The issue is now it is possible for a user to inadvertently drop a control on a page that may already have it included. For example : We include the control on a master page – then again on a page that inherits from this master.

What would be the best way to insure the user control is used only once when rendering the page?

Answer 1

There is no way than to loop all controls and their parents/childs.

For example:

Public Module ExtensionMethods

    <Runtime.CompilerServices.Extension()> _
    Public Function FindControlRecursively(ByVal parentControl As System.Web.UI.Control, ByVal controlType As Type) As System.Web.UI.Control

        If parentControl.GetType = controlType Then
            Return parentControl
        End If

        For Each c As System.Web.UI.Control In parentControl.Controls
            Dim child As System.Web.UI.Control = FindControlRecursively(c, controlType)
            If child IsNot Nothing Then
                Return child
            End If
        Next

        Return Nothing

    End Function

End Module

and you can check it so:

If Not FindControlRecursively(Me.Page.Master, GetType(UC_Status)) Is Nothing Then
   'thow exception or whatever'
End If

Note: all untested