Gridview in checkbox asp net update panel

Hello everyone, my problem is that I'm exporting the gridview to another gridview with the selected checkbox data. But if I use an update panel this does not work. How can I solve this problem.

Code Behind

  protected void chcsec_CheckedChanged(object sender, EventArgs e)
        {


            if ((sender as CheckBox).Checked)
            {
                if (ViewState["CheckedRow"] == null)
                {
                    DataTable dt = CheckedData();
                    ViewState["CheckedRow"] = dt;
                }
                else
                {
                    DataTable previousCheckedRows = ViewState["CheckedRow"] as DataTable;
                    DataTable dtCurrentCheckedRows = CheckedData();
                    dtCurrentCheckedRows.Merge(previousCheckedRows);
                    ViewState["CheckedRow"] = dtCurrentCheckedRows;
                }
            }
            else
            {
                GridViewRow row = ((sender as CheckBox).NamingContainer as GridViewRow);
                Label lblUrun = (row.FindControl("lblUrun") as Label);
                Label lblStok = (row.FindControl("lblStok") as Label);

                DataTable deleteRow = (ViewState["CheckedRow"] as DataTable).DefaultView.ToTable(true);
                DataRow[] dr = deleteRow.Select("UrunAd = '" + lblUrun.Text + "' AND Stok = '" + lblStok.Text + "'");
                foreach (DataRow d in dr)
                {
                    deleteRow.Rows.Remove(d);
                }
                ViewState["CheckedRow"] = deleteRow;
            }
            gvSiparis.DataSource = (ViewState["CheckedRow"] as DataTable).DefaultView.ToTable(true);
            gvSiparis.DataBind();

        }


        private DataTable CheckedData()
        {
            DataTable dt = new DataTable();
            dt.Columns.AddRange(new DataColumn[] { new DataColumn("UrunAd"), new DataColumn("Stok", typeof(int)) });
            foreach (GridViewRow rw in example.Rows)
            {

                if (rw.RowType == DataControlRowType.DataRow)
                {

                    CheckBox chk = (CheckBox)rw.Cells[0].FindControl("chcsec");
                    if (chk.Checked)
                    {
                        //HiddenField hdID = (HiddenField)rw.Cells[0].FindControl("hdID");
                        Label lb = (Label)rw.Cells[1].FindControl("lblUrun");
                        Label lb1 = (Label)rw.Cells[2].FindControl("lblStok");


                        int stok = Convert.ToInt32(lb1.Text);



                        dt.Rows.Add(lb.Text, lb1.Text);

                        chk.Checked = false;
                    }

                }
            }

            return dt;
        }

Html Code

<asp:UpdatePanel runat="server" UpdateMode="Conditional"><ContentTemplate><asp:GridView ID="example" CssClass="table table-striped table-bordered table-hover" AutoGenerateColumns="false" DataKeyNames="ID" runat="server" ClientIDMode="Static"><Columns><asp:TemplateField HeaderText="Ürün Seç" ItemStyle-Width="10%"><ItemTemplate><asp:CheckBox ID="chcsec" CssClass="form-control" runat="server" AutoPostBack="true" OnCheckedChanged="chcsec_CheckedChanged" /></ItemTemplate></asp:TemplateField><%--   <asp:TemplateField HeaderText="Ürün ID" ItemStyle-Width="100"><ItemTemplate><asp:HiddenField ID="hdID" runat="server" Text='<%# Eval("ID") %>'/><asp:HiddenField ID="hdID" runat="server" Value='<%# Eval("ID") %>' /></ItemTemplate></asp:TemplateField>--%><asp:TemplateField HeaderText="Ürün Ad" ItemStyle-Width="20%"><ItemTemplate><asp:Label ID="lblUrun" runat="server" Text='<%# Eval("UrunAd") %>'></asp:Label></ItemTemplate><EditItemTemplate><asp:TextBox ID="txturunad" runat="server" Text='<%# Eval("UrunAd") %>'></asp:TextBox></EditItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Stok" ItemStyle-Width="10%"><ItemTemplate><asp:Label ID="lblStok" Style="padding: 3px 5px;" runat="server" Text='<%# Eval("Stok") %>'></asp:Label></ItemTemplate><EditItemTemplate><asp:TextBox ID="txtstok" Style="padding: 3px 5px;" runat="server" Text='<%# Eval("Stok") %>'></asp:TextBox></EditItemTemplate></asp:TemplateField><%--   <asp:TemplateField HeaderText="Fiyat" ItemStyle-Width="50"><ItemTemplate><asp:TextBox ID="txtfiyat" Style="padding: 3px 5px; width: 100%" CssClass="form-control" runat="server"></asp:TextBox></ItemTemplate><EditItemTemplate><asp:TextBox ID="txtfiyat" Style="padding: 3px 5px; width: 100%" runat="server" CssClass="form-control"></asp:TextBox></EditItemTemplate></asp:TemplateField>--%><%--     <asp:TemplateField HeaderText="Adet" ItemStyle-Width="50"><ItemTemplate><asp:TextBox ID="txtAdet" Style="padding: 3px 5px; width: 100%" CssClass="form-control" runat="server"></asp:TextBox></ItemTemplate><EditItemTemplate><asp:TextBox ID="txtAdet" runat="server" Style="padding: 3px 5px; width: 100%" CssClass="form-control"></asp:TextBox></EditItemTemplate></asp:TemplateField>--%><%--    <asp:TemplateField HeaderText="Eleman Seç" ItemStyle-Width="100"><ItemTemplate><asp:DropDownList ID="drpEleman" CssClass="form-control" runat="server"></asp:DropDownList></ItemTemplate></asp:TemplateField>--%><%--  <asp:TemplateField HeaderText="Eleman Adet" ItemStyle-Width="50"><ItemTemplate><asp:TextBox ID="txtElemanAdet" Style="padding: 3px 5px; width: 100%" CssClass="form-control" runat="server"></asp:TextBox></ItemTemplate><EditItemTemplate><asp:TextBox ID="txtElemanAdet" runat="server" Style="padding: 3px 5px; width: 100%" CssClass="form-control"></asp:TextBox></EditItemTemplate></asp:TemplateField>--%><%--              <asp:TemplateField HeaderText="Eleman Fiyat" ItemStyle-Width="50"><ItemTemplate><asp:TextBox ID="txtElemanFiyat" Style="padding: 3px 5px; width: 100%" CssClass="form-control" runat="server"></asp:TextBox></ItemTemplate><EditItemTemplate><asp:TextBox ID="txtElemanFiyat" runat="server" Style="padding: 3px 5px; width: 100%" CssClass="form-control"></asp:TextBox></EditItemTemplate></asp:TemplateField>--%><%--   <asp:CommandField ButtonType="Link" ShowEditButton="true" ShowDeleteButton="true" ItemStyle-Width="150" />--%></Columns></asp:GridView></ContentTemplate></asp:UpdatePanel>