Persist data inside Modalpopupextender

I have the following code and I want to persist data inside each textbox control when Cancel button is activated?

<asp:Panel ID="PnlAddress" runat="server"  align="center" style = "display:none" CssClass="modalPopup"><h2 id="PopupHeader" class="PopupHeader">
                                                Item address location</h2><table id="address"  border="0"><tr><th>
                                                        Street Address:</th><td><asp:TextBox ID="TxtAddress" runat="server" MaxLength="100"></asp:TextBox></td></tr><tr><th>
                                                        City/Town:</th><td><asp:TextBox ID="TxtCity" runat="server" MaxLength="20"></asp:TextBox></td></tr><tr><th>
                                                        Region:</th><td><asp:TextBox ID="TxtRegion" runat="server" MaxLength="30"></asp:TextBox></td></tr><tr class="Controls"><td><asp:Button ID="BtnClose" runat="server" Text="Finish"
                                                    ValidationGroup="ADDRESS" /></td><td><asp:Button ID="BtnCancel" runat="server" Text="Cancel" /></td></tr></table></asp:Panel><ajaxToolkit:ModalPopupExtender ID="ModalPopupExtenderAddress" runat="server"  BackgroundCssClass="modalBackground"
                                         CancelControlID="BtnCancel" DropShadow="true"
                                        OkControlID="BtnClose" OnCancelScript="CanAddress()" OnOkScript="performCheck()" PopupControlID="PnlAddress"
                                        TargetControlID="AddressChange" />