working with selected index change event of dropdown INSIDE GRIDVIEW

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C#

Gridview

drop-down

ASP.NET4

i have a grid view which consists of a DROPDOWN and 2 textboxes in each row. after clicking a button (at the footer) the data in the first row should be inserted to DATABASE tables and new row must be created. also whenever the selected index is changed in the DDL the corresponding textboxes in the row must be populated with the selected value of the item selected in the DDL.how should it be done for each new row created inside the grid.
the code for gridview is as follows.

<asp:GridView ID="GridView1" ShowFooter="True" AutoGenerateColumns="False" 
                    runat="server" >
                    <Columns>
                        <asp:TemplateField HeaderText="Products/Services">
                            <ItemTemplate>
                                <asp:DropDownList ID="DropDownProducts" Width="150px" runat="server" CssClass="RegistryDrop"
                                  AutoPostBack="true" OnSelectedIndexChanged="DropDownProducts_SelectedIndexChanged" DataSourceID="datasourceProducts" DataTextField="Name" DataValueField="ProdId">
                                </asp:DropDownList>
                                <asp:SqlDataSource ID="datasourceProducts" runat="server" ConnectionString="<%$ ConnectionStrings:EasyCut %>"
                                    SelectCommand="SELECT [Name], [ProdId] FROM [tbl_ProdServ]"></asp:SqlDataSource>
                            </ItemTemplate>
                        </asp:TemplateField>
                        <asp:TemplateField HeaderText="Price">
                            <ItemTemplate>
                                <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
                            </ItemTemplate>
                        </asp:TemplateField>
                        <asp:TemplateField HeaderText="Quantity">
                            <ItemTemplate>
                                <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
                            </ItemTemplate>
                            <FooterStyle HorizontalAlign="Right" />
                            <FooterTemplate>
                                <asp:Button ID="ButtonAdd" OnClick="btn_add_Click" runat="server" Text="Submit" />
                            </FooterTemplate>
                        </asp:TemplateField>
                    </Columns>
                </asp:GridView>

I tried following approach in the code behind but it doesnt seem to work

protected void DropDownProducts_SelectedIndexChanged(object sender, EventArgs e)
        {
            
            TextBox box1=(TextBox)GridView1.Rows[e.currentrow].Cells[2].FindControl("TextBox2");
            DropDownList dl=(DropDownList)GridView1.Rows[e.currentrow].Cells[2].FindControl("DropDownProducts");

            box1.Text = dl.SelectedValue.ToString();
        }