how to get values from asp gridview to code behind to updat

Question

how to get values from asp gridview to code behind to update.

 

label can get values. but text box value  not gettig.   its getting empty from text box.

 

<asp:GridView ID="grvItemDetails" runat="server"

ShowFooter="True" AutoGenerateColumns="False"

CellPadding="4" ForeColor="#333333"

GridLines="None" OnRowDeleting="grvStudentDetails_RowDeleting">

<Columns>

<asp:BoundField DataField="RowNumber" HeaderText="SNo" />

<asp:BoundField DataField="itemid" HeaderText="Item Id" Visible="true" />

<asp:BoundField HeaderText="Item Name"

DataField="itemname"

SortExpression="itemname"></asp:BoundField>

<%--<asp:TemplateField HeaderText="Item Name">

<ItemTemplate>

<asp:TextBox ID="itemname" runat="server"></asp:TextBox>

</ItemTemplate>

</asp:TemplateField>--%>

<asp:TemplateField HeaderText="Weight">

<ItemTemplate>

<asp:TextBox ID="wieght" runat="server"></asp:TextBox>

</ItemTemplate>

</asp:TemplateField>

<asp:TemplateField HeaderText="Price">

<ItemTemplate>

<asp:TextBox ID="price" runat="server" ></asp:TextBox>

</ItemTemplate>

</asp:TemplateField>

<asp:CommandField ShowDeleteButton="True" />

<%-- <asp:Button ID="ButtonAdd" runat="server"

Text="Add Image " />--%>

<%-- <asp:ImageField HeaderText="Picture">

</asp:ImageField>--%>

</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" />

<SortedAscendingCellStyle BackColor="#F5F7FB" />

<SortedAscendingHeaderStyle BackColor="#6D95E1" />

<SortedDescendingCellStyle BackColor="#E9EBEF" />

<SortedDescendingHeaderStyle BackColor="#4870BE" />

</asp:GridView>