DropDownList Added In Runtime - Event Handler Not Getting Fired

Protected Sub ddl_selectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
Dim a As String = ""
'this does not get fired
End Sub
<asp:GridView ID="GridViewAssignment" runat="server" BackColor="White" BorderColor="White"
BorderStyle="Ridge" BorderWidth="2px" CellPadding="3" CellSpacing="1" GridLines="None"
Width="100%">
<RowStyle BackColor="#DEDFDE" ForeColor="Black" />
<FooterStyle BackColor="#C6C3C6" ForeColor="Black" />
<PagerStyle BackColor="#C6C3C6" ForeColor="Black" HorizontalAlign="Right" />
<SelectedRowStyle BackColor="#86A4CA" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="#808080" Font-Bold="True" ForeColor="#E7E7FF" />
</asp:GridView>
Protected Sub GridViewAssignment_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridViewAssignment.RowDataBound
Dim dateApplicationCreatedCell As TableCell = e.Row.Cells(0) 'app created on
Dim typeOfReview As TableCell = e.Row.Cells(7) 'type
Dim QCCell As TableCell = e.Row.Cells(8) 'qc
Dim dateReviewAssignedCell As TableCell = e.Row.Cells(9) 'date assigned
Dim reviewerNameCell As TableCell = e.Row.Cells(10) 'reviewer
Dim dateReviewCompletedCell As TableCell = e.Row.Cells(11) 'date completed review
Dim ddl As DropDownList
If e.Row.RowIndex <> -1 Then
If dateReviewAssignedCell.Text.Trim = " " Then
dateReviewAssignedCell.Text = Now.Date
End If
Dim sqlCondition As String = String.Empty
If dateReviewCompletedCell.Text.Trim = " " Then
Dim nameToSelect As String
If reviewerNameCell.Text.Trim <> " " Then
Dim dateReviewAssigned As Date = dateReviewAssignedCell.Text
Dim elapsedSinceAssigned As Long = DateDiff(DateInterval.Day, dateReviewAssigned.Date, Now.Date, Microsoft.VisualBasic.FirstDayOfWeek.Monday, FirstWeekOfYear.Jan1)...............................