Dropdownlist SelectedIndexChanged Not Firing in Custom Gridview Server Control - asp.net

Question

I am building a custom ASP.Net gridview server control (not user control) with a custom pager. The custom pager contains a dynamically added dropdownlist which changes the gridview's pagesize (items per page). The dropdownlist is added in the RenderChildren method which I am overriding in the server control's code.
I am basically cloning the default pager row and adding the dropdownlist into the row, then adding the cloned pager row to the gridview and destroying the original.
The problem is that even though the dropdownlist's autopostback property is set to true and I am adding an event handler for it, I cannot get the event to fire when changing the selectedindex. I have tried several different approaches with no luck.
I believe the problem is that the dropdownlist has not yet been rendered by the time the selectedindex is changed in the calling page. But I don't know enough about server controls and the page lifecycle to figure out how to resolve it.
Here is an abbreviated version of the code:
Public Class CustomGridView
Inherits System.Web.UI.WebControls.GridView
Implements IPostBackEventHandler
Protected WithEvents mctlDropdownListPageSize As New DropDownList
Public Event PageSizeChanged(ByVal sender As Object, ByVal e As EventArgs)
Protected Sub dropdownListPageSize_Click(ByVal sender As Object, ByVal e As EventArgs)
RaiseEvent PageSizeChanged(Me.mctlDropdownListPageSize, e)
End Sub
'This sets up paging using the pageddatasource
Protected Overrides Sub InitializePager(row As GridViewRow, columnSpan As Integer, pagedDataSource As PagedDataSource)
pagedDataSource.AllowPaging = True
pagedDataSource.AllowCustomPaging = True
pagedDataSource.VirtualCount = TotalRows
pagedDataSource.CurrentPageIndex = CurrentPageIndex
Me.PageIndex = CurrentPageIndex
MyBase.InitializePager(row, columnSpan, pagedDataSource)
End Sub
Protected Overrides Sub RenderChildren(writer As HtmlTextWriter)
Try
If Me.Controls.Count = 0 Then
' nothing to render, use default
MyBase.RenderChildren(writer)
Return
End If
' select the header row in the grid
Dim gridViewTable As WebControl = DirectCast(Me.Controls(0), WebControl) ' the table
' the table->row(0) if no top paging, otherwise row(1)
Dim pagerRow As GridViewRow = gridViewTable.Controls(0)
'Get the pager cell -- we want only one cell containing all the elements
Dim pagerContainerCell As TableCell = pagerRow.Cells(0)
'Create the new table which will contain the title, results summary and pager
Dim newPagerTable As New Table
newPagerTable.CellPadding = 0
newPagerTable.CellSpacing = 0
newPagerTable.CssClass = "section_headers gridpagertable"
'Create a table row to contain the new cells
Dim newPagerRow As New TableRow
newPagerRow.CssClass = "pagerrow"
'Create 2 cells to hold the new controls + pager
Dim resultsCell As New TableCell
resultsCell.CssClass = "results"
Dim pagerCell As New TableCell
pagerCell.CssClass = "pager"
If Me.AllowPaging Then
'Add the pagesize dropdown and results summary text
'Create the results label
Dim mctlResultsLabelText As New LiteralControl
mctlResultsLabelText.Text = "<span>Results per page </span>"
'Create the pagesize dropdown container div
Dim mctlResultsDropdownListContainerDiv As New HtmlControls.HtmlGenericControl("div")
mctlResultsDropdownListContainerDiv.Attributes("class") = "dropdown_select"
Dim mctlResultsDropdownListLabel As New HtmlControls.HtmlGenericControl("label")
'Create the pagesize dropdownlist
mctlDropdownListPageSize.ID = "dropDownListPageSize"
mctlDropdownListPageSize.Items.Add(New ListItem("100", "100"))
mctlDropdownListPageSize.Items.Add(New ListItem("200", "200"))
mctlDropdownListPageSize.Items.Add(New ListItem("300", "300"))
mctlDropdownListPageSize.AutoPostBack = True
mctlDropdownListPageSize.EnableViewState = True
AddHandler mctlDropdownListPageSize.SelectedIndexChanged, AddressOf Me.dropdownListPageSize_Click
'Add the dropdown tot he dropdown container div
mctlResultsDropdownListLabel.Controls.Add(mctlDropdownListPageSize)
mctlResultsDropdownListContainerDiv.Controls.Add(mctlResultsDropdownListLabel)
'Add the results drpdown label
resultsCell.Controls.Add(mctlResultsLabelText)
'Add the pagesize dropdown
resultsCell.Controls.Add(mctlResultsDropdownListContainerDiv)
'Add the cell to the row
newPagerRow.Controls.Add(resultsCell)
End If
'Add the pager control and action icons
Dim mctlPagerContainerDiv As New HtmlControls.HtmlGenericControl("div")
mctlPagerContainerDiv.Attributes.Add("class", "pagination")
'Add the div to the pager cell
pagerCell.Controls.Add(mctlPagerContainerDiv)
If Me.AllowPaging Then
'Get the existing pager container table with the pager buttons
Dim tblPager As Table
tblPager = pagerContainerCell.Controls(0)
tblPager.CellPadding = 0
'Add the pager to the cell
pagerCell.Controls.Add(tblPager)
End If
'Add the cell to the row
newPagerRow.Controls.Add(pagerCell)
'Add the row to the table
newPagerTable.Controls.Add(newPagerRow)
'Render the new pager row (table+row+3 new cells with controls)
newPagerTable.RenderControl(writer)
If Me.AllowPaging Then
' remove the original (default) pager row, otherwise we have two
gridViewTable.Controls.RemoveAt(0)
End If
'Render the gridview
gridViewTable.RenderControl(writer)
Catch ex As Exception
ControlErrorHandler(ex, "RenderChildren")
End Try
End Sub
Private Sub ControlErrorHandler(ByVal ex As Exception, ByVal methodName As String)
Throw New ApplicationException(Me.GetType().ToString & "." & methodName & " failed due to the inner error - " & ex.Message, ex)
End Sub
<Description("The current page index of the gridview."), DefaultValue(""), Themeable(False), Category("Appearance")> _
Public Property CurrentPageIndex() As Integer
Get
If Not ViewState(VSKeyCurrPageIndex) Is Nothing Then
Return Integer.Parse(ViewState(VSKeyCurrPageIndex))
Else
Return 0
End If
End Get
Set(value As Integer)
ViewState(VSKeyCurrPageIndex) = value
End Set
End Property
End Class
The calling page has this:
Private Sub gridViewResults_PageSizeChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles gridViewResults.PageSizeChanged
'
End Sub
I have looked at almost every related issue here on Stackoverflow, as well as other possible solutions in posts and article online. Any insight or suggestions will be appreciated.