I worte code for edit,update,delete but by clicking edit button the table is disapeared

<asp:GridView ID="gvdetails" runat="server" AutoGenerateColumns="false"
            AllowPaging="true" PageSize="5"
             OnRowEditing="gvdetails_RowEditing" OnRowDeleting="gvdetails_RowDeleting" OnRowUpdating="gvdetails_RowUpdating" DataKeyNames="UserId,UserName"
              OnRowCancelingEdit="gvdetails_RowCancelingEdit"  OnPageIndexChanging="gvdetails_PageIndexChanging">

        <PagerSettings Mode="NumericFirstLast" PageButtonCount="5" FirstPageText="Firstpage" NextPageText="Nextpage" />
        <Columns>
        <asp:TemplateField>
        <EditItemTemplate>
        <asp:ImageButton ID="imgbtnUpdate" CommandName="Update" runat="server" ImageUrl="~/Images/update.jpg" ToolTip="Update" Height="20px" Width="20px" />
        <asp:ImageButton ID="imgbtnCancel" CommandName="Cancel" runat="server" ImageUrl="~/Images/Button cancel Icon.jpg" ToolTip="Cancel" Height="20px" Width="20px" />
        </EditItemTemplate>
        <ItemTemplate>
        <asp:ImageButton ID="imgbtnEdit" CommandName="Edit" runat="server" ImageUrl="~/Images/Edit Icon.jpg" ToolTip="Edit" Height="20px" Width="20px" />
        <asp:ImageButton ID="imgbtnDelete" CommandName="Delete" runat="server" ImageUrl="~/Images/Delete.jpg" ToolTip="Delete" Height="20px" Width="20px" />
        </ItemTemplate>
        </asp:TemplateField>

       <asp:TemplateField HeaderText="UserName">
       <ItemTemplate>
       <asp:Label ID="lblitmusr" runat="server" Text='<%#Eval("UserName")%>'></asp:Label>
       </ItemTemplate>
       <EditItemTemplate>
<%--         <asp:Label ID="Label1" runat="server" Text='<%#Eval("UserName") %>'></asp:Label> // line Comment by sanwar--%>
       <asp:TextBox ID="lbleditusr" runat="server" Text='<%#Eval("UserName") %>'></asp:TextBox>  <%--// line add by sanwar--%>
       </EditItemTemplate>
       </asp:TemplateField>
       <asp:TemplateField HeaderText="City">
       <ItemTemplate>
       <asp:Label ID="lblitmcity" runat="server" Text='<%#Eval("City") %>' ></asp:Label>
       </ItemTemplate>
       <EditItemTemplate>
<%--  <asp:Label ID="Label1" runat="server" Text='<%#Eval("City") %>'></asp:Label>      // line Comment by sanwar--%>
       <asp:TextBox ID="lbleditcity" runat="server" Text='<%#Eval("City") %>'></asp:TextBox>        <%--// line add by sanwar--%>

       </EditItemTemplate>
       </asp:TemplateField>
       <asp:TemplateField HeaderText="Designation">
       <ItemTemplate>
       <asp:Label ID="lblitmdesignation" runat="server" Text='<%#Eval("Designation")%>'></asp:Label>
       </ItemTemplate>
       <EditItemTemplate>
       <%--         <asp:Label ID="lbleditdesignation" runat="server" Text='<%#Eval("Designation") %>'></asp:Label> // line Comment by sanwar--%>
       <asp:TextBox ID="lbleditdesignation" runat="server" Text='<%#Eval("Designation") %>'></asp:TextBox>  <%--// line add by sanwar--%>
       </EditItemTemplate>
       </asp:TemplateField>

        </Columns>

        </asp:GridView>
        <asp:Label ID="lblresult" runat="server"></asp:Label>

protected void Page_Load(object sender, EventArgs e)
   {
       if (!IsPostBack)
       {
           BindGridView();
       }



   }
   protected void BindGridView()
   {
       con.Open();
       SqlCommand cmd = new SqlCommand("select * from GridDetails", con);
       SqlDataAdapter da = new SqlDataAdapter(cmd);
       DataSet ds = new DataSet();
       da.Fill(ds);
       con.Close();
       if (ds.Tables[0].Rows.Count > 0)
       {
           gvdetails.DataSource = ds;
           gvdetails.DataBind();
       }
       else
       {
           ds.Tables[0].Rows.Add(ds.Tables[0].NewRow());
           gvdetails.DataSource = ds;
           gvdetails.DataBind();
           int columncount = gvdetails.Rows[0].Cells.Count;
           gvdetails.Rows[0].Cells.Clear();
           gvdetails.Rows[0].Cells.Add(new TableCell());
           gvdetails.Rows[0].Cells[0].ColumnSpan = columncount;
           gvdetails.Rows[0].Cells[0].Text = "No Records Found";

       }


   }

   protected void gvdetails_RowUpdating(object sender, GridViewUpdateEventArgs e)
   {
       GridViewRow row = (GridViewRow)gvdetails.Rows[e.RowIndex]; // line add by sanwar
       int userid = Convert.ToInt32(gvdetails.DataKeys[e.RowIndex].Value.ToString());
       string username = gvdetails.DataKeys[e.RowIndex].Values["UserName"].ToString();
       TextBox txtcity = (TextBox)row.FindControl("lbleditcity");// line add by sanwar
       // TextBox txtcity = (TextBox)gvdetails.Rows[e.RowIndex].FindControl("txtcity"); // line Comment by sanwar
       TextBox txtDesignation = (TextBox)row.FindControl("lbleditdesignation");// line add by sanwar
       //TextBox txtDesignation = (TextBox)gvdetails.Rows[e.RowIndex].FindControl("txtDesignation");// line Comment by sanwar
       con.Open();
       //SqlCommand cmd = new SqlCommand("update from GridDetails set City='" + txtcity.Text + "',Designation='" + txtDesignation.Text + "' where Userid=" + userid, con);
       SqlCommand cmd = new SqlCommand("update  GridDetails set City='" + txtcity.Text + "',Designation='" + txtDesignation.Text + "' where Userid=" + userid, con); // line Modify by sanwar

       cmd.ExecuteNonQuery();
       con.Close();
       lblresult.Text = username + "Details Updated Successfully";
       gvdetails.EditIndex = -1;
       BindGridView();




   }

   protected void gvdetails_RowEditing(object sender, GridViewEditEventArgs e)
   {
       gvdetails.EditIndex = e.NewEditIndex;
       // gvdetails.DataBind(); // line Comment by sanwar  Note: your table not display because your table data has been lost ,No Bind the data  this region
       BindGridView(); // line add by sanwar
   }

   protected void gvdetails_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
   {
       gvdetails.EditIndex = -1;
       BindGridView();
   }
   protected void gvdetails_RowDeleting(object sender, GridViewDeleteEventArgs e)
   {


       int userid = Convert.ToInt32(gvdetails.DataKeys[e.RowIndex].Values["UserId"].ToString());
       string username = gvdetails.DataKeys[e.RowIndex].Values["UserName"].ToString();
       con.Open();
       SqlCommand cmd = new SqlCommand("delete from GridDetails where UserId=" + userid, con);
       int result = cmd.ExecuteNonQuery();
       con.Close();
       if (result == 1)
       {
           BindGridView();
           lblresult.Text = username + "Details deleted successfully";

       }
   }
   protected void gvdetails_PageIndexChanging(object sender, GridViewPageEventArgs e)
   {
       gvdetails.PageIndex = e.NewPageIndex;
       BindGridView();
   }