How to get data from templet field in gridview - asp.net

Question

Currently i'm working on my final year project.
In a webpage which loads data in gridview, each row has on button which will popup a window and ask for error to write inside **textbox** and submit that error on server.
On the serverside i require two values, first one is the primary key of that row and the error that is written inside **textbox**. It is easy to get primary key value but i'm unable to get value in side the textbox.
I'm attaching the code of .aspx file:
<asp:GridView ID="gvPODetails" runat="server" DataSourceID="Inspection_SqlDataSource"
EnableModelValidation="True" AllowSorting="True" AutoGenerateColumns="False"
BackColor="#CCCCCC" BorderColor="Black" BorderStyle="Solid" BorderWidth="3px" CellPadding="4" ForeColor="Black" CellSpacing="2">
<Columns>
<asp:BoundField DataField="ProductCode" HeaderText="ProductCode" SortExpression="ProductCode" />
<asp:BoundField DataField="MaterialCode" HeaderText="MaterialCode" SortExpression="MaterialCode" />
<asp:TemplateField>
<ItemStyle BorderStyle="None" BorderColor="Transparent" BorderWidth="0px" />
<ItemTemplate>
<asp:LinkButton ID="lnkbtnOk" OnClick="Ok_Click" CommandArgument='<%# Eval("Identity")%>'
runat="server" Text="Ok"></asp:LinkButton>
<asp:LinkButton ID="lnkbtnReject" runat="server" Text="Reject"></asp:LinkButton>
<asp:Panel ID="popUp_Data" runat="server" CssClass="modelPopup" Style="display: none;">
<table style="padding: 10px 10px 10px 10px; width: 100%;">
<tr>
<td>
</td>
<td align="right">
<input id="close_popup" type="image" src="../Images/closebox.gif" />
</td>
</tr>
<tr valign="top">
<td align="right">
<asp:Label ID="lblError" Text="Error" runat="server" CssClass="fontStyle"></asp:Label>
</td>
<td align="left">
<asp:TextBox ID="txtError" runat="server" CssClass="ta"
TextMode="MultiLine"></asp:TextBox>
</td>
</tr>
<tr>
<td>
</td>
<td align="left">
<asp:Button ID="btnSubmit" runat="server" CssClass="sbmt" Text="Reject Item" OnClick="Reject_Click"
CommandArgument='<%# Eval("Identity")%>' />
</td>
</tr>
</table>
</asp:Panel>
<asp:ModalPopupExtender ID="popUp_Data_ModalPopupExtender" runat="server" DynamicServicePath=""
Enabled="True" BackgroundCssClass="modelBackground" PopupControlID="popUp_Data"
TargetControlID="lnkbtnReject" CancelControlID="close_popup">
</asp:ModalPopupExtender>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<EmptyDataTemplate>
<asp:Label runat="server" ID="lblNoDataFound" Text="No Machine Found."></asp:Label>
</EmptyDataTemplate>
</asp:GridView>
What i want is the data inside textbox with id txtError.

Answer 1

Since it is a repeating item, you cannot access it directly using its id. You can use FindControl instead as follows:
var textBoxAux = gridView.Rows[index].FindControl("txtError") as TextBox;
You need to find the index of the row in the event you are handling.
EDIT: finding the index...
Pass the DataItemIndex in the CommandArgument ( instead of the identity ) if applicable.
CommandArgument='<%# Container.DataItemIndex %>'
Ref: ASP.NET GridView RowIndex As CommandArgument