How to dynamically populate a dropdownlist in a gridview header row

Question

I have a gridview which contains a dropdownlist in the header row to allow users to filter the data:

<asp:GridView ID="GV_Projects" runat="server" AutoGenerateColumns="False" CssClass="mGrid"
                        PagerStyle-CssClass="pgr" AlternatingRowStyle-CssClass="alt" DataKeyNames="Title"
                        OnRowDataBound="OnRowDataBound" EnableModelValidation="True" Style="width: 95%;
                        float: left;">
                        <AlternatingRowStyle CssClass="alt"></AlternatingRowStyle>
                        <Columns>
                            <asp:BoundField DataField="Title" HeaderText="Title" />
                            <asp:BoundField ItemStyle-Width="150px" DataField="Developer" HeaderText="Developer" />
                            <asp:TemplateField>
                                <HeaderTemplate>
                                    Division<br />
                                    <asp:DropDownList ID="DDL_DivisionFilter" runat="server" AutoPostBack="True">
                                        <asp:ListItem>All</asp:ListItem>
                                    </asp:DropDownList>
                                </HeaderTemplate>
                                <ItemTemplate>
                                    <%# Eval("Division") %>
                                </ItemTemplate>
                            </asp:TemplateField>
                            </Columns>
                        <PagerStyle CssClass="pgr"></PagerStyle>
                    </asp:GridView>

Within my code I attempt to populate this dynamically based on results from a query:

GridViewRow row = GV_Projects.HeaderRow;
DropDownList DDL_Division = new DropDownList();           
DDL_Division = (DropDownList)row.FindControl("DDL_DivisionFilter");

make connection, query add each result to drop down list            

however everytime it gets to "(dropdownlist)row.FindControl("DDL_DivisionFilter") it errors out as a "NullReferenceException" I just can't understand why the variable row is null, I have only recently switched from vb to c# so am not quite there with fixing this.

Answer 1

I was trying to populate the dropdown before I had done a databind on the gridview. I called a sub to populate the drop down (shown above) and then another call to populate the gridview. When I switched these calls around it all ran fine. I believe this is because the gridview wasn't actually there hence the null reference when I tried to initialise row.