Textbox in the GridView footer template returns null when clicking linkbutton

Hi All,
I cannot get the textbox value in the footer template of GridView control when clicking on the linkbutton. I have no idea when the problem is. Below is my code:
.aspx page code
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"             ondatabound="GridView1_DataBound" ShowFooter ="True"             EmptyDataText="No record" >             <Columns>                 <asp:TemplateField HeaderText="Form Name">                     <EditItemTemplate>     &nbs ...