Question

I am designing a user control that attempts to create a filter bar with various TextBox or DropDownList elements on the page according to the sample markup below:

<gf:GridFilterBar runat="server">
    <filters>
        <filter Label="Field1" Type="TextBox" />
        <filter Label="Field2" Type="DropDownList" />
    </filters>
</gf:GridFilterBar>

Using inspiration from another post, I have created code behind that properly parses this markup and reads in the properties of each intended child control. The issue I am having is when it comes time to actually render this information on the screen. Every control I initialize from within the “New” sub of the “Filter” class never appears on the screen. When I place a breakpoint in the “New” sub and follow what is happening, I can see the Filter.New sub being traversed twice and the values being read in, but nothing else I initialize from within that sub has any effect on the page even though, as far as I can tell, it is all being created successfully. Here is a sample of the code with just the Label property being read:

Imports System
Imports System.Collections
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls


Public Class GridFilterBar
Inherits System.Web.UI.UserControl

Private _Filters As New FiltersClass(Me)

<PersistenceMode(PersistenceMode.InnerProperty)> _
Public ReadOnly Property Filters() As FiltersClass
    Get
        Return _Filters
    End Get
End Property

Private Sub Page_Init(sender As Object, e As System.EventArgs) Handles Me.Init
    DDL.Visible = True
End Sub
End Class

Public Class FiltersClass
Inherits ControlCollection

Public Sub New(ByVal owner As Control)
    MyBase.New(owner)
End Sub

Public Overrides Sub Add(ByVal child As System.Web.UI.Control)
    MyBase.Add(New Filter(child))
End Sub

End Class

Public Class Filter
Inherits HtmlGenericControl

Public Sub New(ByVal GenericControl As HtmlGenericControl)
    Label = GenericControl.Attributes("Label")
    Dim lit As New Literal
    lit.Text = Label.ToString
    Me.Controls.Add(lit)
End Sub

Public Property Label As String = String.Empty

Public Overrides Function ToString() As String
    Return Me.Label
End Function

End Class

Can anyone spot what I’m doing wrong?

Answer 1

I was able to answer my question. I added an override sub for CreateChildControls in my main class and used a For Each loop to grab the properties set from each newly initialized “Filter”

Protected Overrides Sub CreateChildControls()

    For Each filter In Filters

        Dim lit As New Literal
        lit.Text = filter.Label
        Controls.Add(lit)

    Next filter

End Sub

This relegated the Filter.New sub to simply grabbing the properties:

Public Sub New(ByVal GenericControl As HtmlGenericControl)
    Label = GenericControl.Attributes("Label")
End Sub