Forms Data Controls :: Get Checkbox Control From Gridview Template Column?

I have a gridview control

i add template column dynamically to gridview

like this in a function in AddColumns button clickevent

gv.Columns.Clear()
Dim chkCol As New TemplateField
chkCol.ItemStyle.Width = 20
chkCol.ItemStyle.HorizontalAlign = HorizontalAlign.Center
gv.Columns.Add(chkCol)

2)

and in row databound event i added checkbox control to this template field. like this

Protected Sub gv_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles gv.RowDataBound
If e.Row.RowType = DataControlRowType.DataRow Then
Dim chkbox As New CheckBox
chkbox.ID = "chkSelect"
e.Row.Cells(0).Controls.Add(chkbox)
End If
End Sub

HERE I WANT TO GET CHEKC BOX IN btnok click event

Protected Sub btnOk_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnOk.Click
Dim linkId As String
Dim summary As String = ""
'Enumerate the GridViewRows
For index As Integer = 0 To Me.gv.Rows.Count - 1
'Programmatically access the CheckBox from the TemplateField
Dim cb As CheckBox = CType(gv.Rows(index).Cells(0).FindControl("chkSelect"), CheckBox)
If cb IsNot Nothing Then
If cb.Checked Then
linkId = Me.gv.DataKeys(index).Value
End If
End If
Next
Me.Page.Title = linkId
End Sub

But here i am not getting Check box even i used find control. how i get checkbox