formview asp.net items return null edit mode

<asp:FormView ID="fvAdminPro" runat="server" OnModeChanging="fvAdminPro_ModeChanging" Height="277px" OnItemUpdated="fvAdminPro_ItemUpdated" OnItemUpdating="fvAdminPro_ItemUpdating" OnPageIndexChanging="fvAdminPro_PageIndexChanging" Width="88px">

<EditItemTemplate>

  <asp:TextBox ID="fNametxt" runat="server" Text='<%# Bind("FirstName") %>'></asp:TextBox>
    </EditItemTemplate>
    </asp:FormView>


    code behinde


     protected void fvAdminPro_ItemUpdating(object sender, FormViewUpdateEventArgs e)
    {



            string test = ((TextBox)(fvAdminPro.Row.FindControl("fNametxt"))).Text;

             //test always return null
            }