refresh gridview after dropdownlist is changed

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C#

ASP.NET4

Hi,

I have gridview and inside that there is a dropdownlist for "items". after choosing the item, i will need to get the rest of the columns filled based on a table in DB.

Gridview:

<asp:GridView ID="grvStudentDetails" runat="server" ShowFooter="True" AutoGenerateColumns="False"
                CellPadding="4" ForeColor="#333333" GridLines="None" OnRowDeleting="grvStudentDetails_RowDeleting"
                Width="97%" Style="text-align: left" 
                onselectedindexchanged="grvStudentDetails_SelectedIndexChanged">
                <Columns>
                    <asp:BoundField DataField="RowNumber" HeaderText="SNo" />
                    <asp:TemplateField HeaderText="Material Description">
                        <ItemTemplate>
                            <asp:dropdownlist ID="txtName" runat="server" MaxLength="200">
                            
                            <asp:ListItem>Select</asp:ListItem>
                            <asp:ListItem >KSPAN5</asp:ListItem>
                            <asp:ListItem >KSPAN6</asp:ListItem>
                            
                            
                            </asp:dropdownlist>
                            
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Units">
                        <ItemTemplate>
                            <asp:TextBox ID="txtAge" runat="server" MaxLength="3" Width="66px"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="txtAge"
                                ErrorMessage="*" SetFocusOnError="True"></asp:RequiredFieldValidator>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Qty">
                        <ItemTemplate>
                            <asp:TextBox ID="txtAddress" runat="server" MaxLength="3" Width="66px"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="txtAddress"
                                ErrorMessage="*" SetFocusOnError="True"></asp:RequiredFieldValidator>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Remarks">
                        <ItemTemplate>
                            <asp:TextBox ID="RBLGender" runat="server" RepeatDirection="Horizontal"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ControlToValidate="RBLGender"
                                ErrorMessage="*" SetFocusOnError="True"></asp:RequiredFieldValidator>
                        </ItemTemplate>
                        <FooterStyle HorizontalAlign="Right" />
                        <FooterTemplate>
                            <asp:Button ID="ButtonAdd" runat="server" Text="Add New Row" OnClick="ButtonAdd_Click" />
                        </FooterTemplate>
                    </asp:TemplateField>
                    <asp:CommandField ShowDeleteButton="True" ControlStyle-Width="100%" />
                </Columns>
                <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                <RowStyle BackColor="#EFF3FB" />
                <EditRowStyle BackColor="#2461BF" />
                <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
                <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
                <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                <AlternatingRowStyle BackColor="White" />
            </asp:GridView>

Where can i write the code if the list changed inside the gridview and if someone can just give me in text what should be done to get the rest of the fields filled after the selection is made?