protected void DropDownList23_SelectedIndexChanged(object sender, EventArgs e)
    {
        DropDownList method = (DropDownList)sender;
        Label7.Text = method.SelectedValue;
    }
    protected void DropDownList23_DataBound(object sender, EventArgs e)
    {
        DropDownList method = (DropDownList)sender;
        Label7.Text = method.SelectedValue;
    }

<asp:TemplateField HeaderText="Параметры метода" SortExpression="riname">
                                                <EditItemTemplate>
                                                    <asp:DropDownList ID="DropDownList24" runat="server" DataSourceID="SqlDataSource100" DataTextField="fullname" DataValueField="ID" SelectedValue='<%# Bind("RI_ID", "{0}") %>' AutoPostBack="True">
                                                    </asp:DropDownList>
                                                    <asp:SqlDataSource ID="SqlDataSource100" runat="server" ConnectionString="<%$ ConnectionStrings:Math %>" SelectCommand="SELECT [fullname], [ID] FROM [RI] WHERE ([methodID] = @methodID)">
                                                     <SelectParameters>
                                                                 <asp:ControlParameter ControlID="Label7" DefaultValue="" Name="methodID" PropertyName="Text" Type="Int32" />
                                                     </SelectParameters>
                                                    </asp:SqlDataSource>
                                                </EditItemTemplate>
                                                <ItemTemplate>
                                                    <asp:Label ID="Label2" runat="server" Text='<%# Bind("riname") %>'></asp:Label>
                                                </ItemTemplate>
                                            </asp:TemplateField>

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if(e.Row.RowState == DataControlRowState.Edit) {
             System.Data.DataRowView dv = (System.Data.DataRowView)e.Row.DataItem;
             
             DropDownList p= (DropDownList)e.Row.FindControl("DropDownList24");
             p.DataBind();
             p.SelectedValue = dv["RI_ID"].ToString();   
        }
    }