Accessing control in a gridview from code behind

Protected Sub GridView1_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles GridView1.PreRender

For Each gvRow In GridView1.Rows
 If gvRow.RowType = DataControlRowType.DataRow Then
   Dim h1 As HyperLink = CType(gvRow.Cells(0).Controls(0), HyperLink)
   h1.NavigateUrl = h1.NavigateUrl & "&H=" & Request.QueryString("H")
 End If
Next

End Sub