View Full Version : [CLOSED] Session NullException

Feb 01, 2012, 7:34 PM

Well. I see it as no your problem, but I would be grateful for any help or hint.

Because a decision out of my scope, our application (run in our own servers) will connect in databases (SQL Server 2000) located in customer webserver. Becaise of this, I need save the connectionString in Session (or HttpContext.Current.Session).

It happens that, when loading or refreshing the grids (gridPanels), when I try to get the connectionstring of the session, it returns me a NullException.
I read somewhere that this is possibly because of asynchronous call.

Have you ever had this problem? is there any workaround?

If there is another hint where I can store my connectionstring for each user and retrieve it at the time to load (and reload) the grids, I would be very grateful.

Thanks for any help.

Feb 01, 2012, 8:44 PM

I think you should just keep Session alive.

If you would google with "session keep alive" you will get many info about it.

Within Ext.NET you could use a TaskManager to "kick" a server:

Every 100 seconds should be enough.

Feb 02, 2012, 1:07 PM
Hi Daniil.. thanks for your answer!

Well... I´m not sure that the problem is a session time-out. I set in my webconfig the session time-out to 20 minutes, and the problem occurss few seconds after the application starts.

it seems to me, the problem occurs after an asynchronous request to load or reload of the gridPanel. My source data is a SQL Server 2008, and my Store Proxy is a WebMethod of my WebService.

I created a test project that exemplifies this bug:
A gridPanel bind to a WebService.
The WebService has two methods. One return a ext.net.Paging and other return a session value.
In default.aspx Page_Load, I set in Session a value.
In default.aspx, there are a button. If you click in this button, trigger a function that consumes the WebService1.GetSessionValue. Its work.
The gridPanel is load with values returned by Webservice1... its work to.
If you mark the checkbox to 'Show Session Value in Webservice1.getData when refresh gridPanel', and click in 'refresh' button of bottonbar of gridPanel, in the getData, a code that try get Session value and Show in a Message box is enable. But this code triggers a Null Exception erro when try get Session value.

I know this is not your responsibility, but if you can take a look and tell me if you have any idea, I'll be very grateful...

Follow the Test Project code:

class Customer

Public Class Customer
Private mvarCode As Long
Private mvarName As String
Private mvarBirthDate As Date

Public Sub New()
mvarCode = 0
mvarName = ""
mvarBirthDate = #1/1/0900#
End Sub

Public Sub New(pCode As Long, pName As String, pBirthDate As Date)
mvarCode = pCode
mvarName = pName
mvarBirthDate = pBirthDate
End Sub

Public Property Code As Long
Return mvarCode
End Get
Set(value As Long)
mvarCode = value
End Set
End Property

Public Property Name As String
Return mvarName
End Get
Set(value As String)
mvarName = value
End Set
End Property

Public Property BirthDate As Date
Return mvarBirthDate
End Get
Set(value As Date)
mvarBirthDate = value
End Set
End Property

End Class


' To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
' <System.Web.Script.Services.ScriptService()> _
<System.Web.Services.WebService(Namespace:="http://tempuri.org/")> _
<System.Web.Services.WebServiceBinding(ConformsTo:= WsiProfiles.BasicProfile1_1)> _
<ToolboxItem(False)> _
Public Class WebService1
Inherits System.Web.Services.WebService

<WebMethod()> _
<ScriptMethod()> _
Public Function GetData(start As Long, limit As Long, sort As String, filter As String) As Paging(Of Customer)
Dim vList As List(Of Customer) = New List(Of Customer)

If filter = "True" Then
End If

vList.Add(New Customer(1, "José Roberto", #1/2/1978#))
vList.Add(New Customer(2, "Fabio Zatta", #4/24/1976#))
vList.Add(New Customer(3, "Kelly Esperança", #5/21/1982#))
vList.Add(New Customer(4, "Veríssimo Rizzi", #6/19/1981#))

Return New Ext.Net.Paging(Of Customer)(vList, vList.Count)

End Function

<WebMethod()> _
<ScriptMethod()> _
Public Function GetSessionValue() As String
Return HttpContext.Current.Session("MySessionValue")
End Function

End Class


<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="WebApplication1._Default" %>
<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Session.Add("MySessionValue", "This is my Session Value!")
End Sub

Protected Sub ShowSession(sender As Object, e As DirectEventArgs)
Dim vmsg As Ext.Net.MessageBox = New Ext.Net.MessageBox
Dim ws As WebApplication1.WebService1 = New WebApplication1.WebService1
vmsg.Alert("Session Value", ws.GetSessionValue)
End Sub


<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Session NullException</title>

<script type="text/javascript">

function getFilter() {
var sFilter = "0";

sFilter = Session.Test.chkReadSessionValue.getValue();

return sFilter;


<ext:ResourceManager ID="resManager1" runat="server" Locale="pt-BR" Namespace="Session.Test"/>
<ext:Panel runat="server" X="5" Y="5" Layout="AbsoluteLayout" Height="400" Width="600">
<ext:Button runat="server" id="btnShowSessionValue" text="Show Session Value" x="50" y="5" width="300" heigth="50">
<Click OnEvent="ShowSession" />
<ext:Checkbox runat="server" ID="chkReadSessionValue" x="50" Y="30"/>
<ext:DisplayField ID="DisplayField1" runat="server" Text="Show Session Value in Webservice1.getData when refresh gridPanel" x="80" Y="30" Width="400"/>
<ext:GridPanel runat="server" ID="grid1" Title="Customers" Frame="true" Layout="FitLayout" IconCls="icon-sugestoes" ButtonAlign="Right" x="50" Y="50" Width="500" Height="300">
<ext:Store ID="Store1" runat="server" RemoteSort="true" PageSize="10">
<ext:AjaxProxy Json="true" Url="~/WebService1.asmx/GetData">
<ActionMethods Read="POST" />
<ext:JsonReader Root="d.Data" TotalProperty="d.TotalRecords" />
<ext:Parameter Name="start" Value="0" Mode="Raw" />
<ext:Parameter Name="limit" Value="10" Mode="Raw" />
<ext:StoreParameter Name="filter" Value="getFilter()" Mode="Raw" />
<ext:Model runat="server" IDProperty="Code" ID="ctl10">
<ext:ModelField Name="Code" />
<ext:ModelField Name="Name" />
<ext:DataSorter Property="Code" Direction="DESC" />
<ColumnModel runat="server" ID="columnmodel1">
<ext:Column runat="server" Text="ID" DataIndex="Code" Width="75px" Sortable="true" />
<ext:Column runat="server" ID="Name" Text="Name" DataIndex="Name" Width="400px" Sortable="true" />
<ext:PagingToolbar ID="tbPagingSugestoes" runat="server" DisplayInfo="true"
DisplayMsg="List {0} - {1} of {2}" EmptyMsg="No records">
<ext:Label ID="Label1" runat="server" Text="Page Size:" />
<ext:ToolbarSpacer runat="server" Width="10" />
<ext:ComboBox ID="cmbPageSize" runat="server" Width="80">
<ext:ListItem Text="5" />
<ext:ListItem Text="10" />
<ext:ListItem Text="15" />
<ext:ListItem Text="20" />
<ext:ListItem Text="25" />
<ext:ListItem Text="30" />
<ext:ListItem Value="10" />
<Select Handler="#{grid1}.store.pageSize = parseInt(this.getValue(), 10); #{grid1}.store.load({params:{start:0}});" />


Feb 02, 2012, 4:51 PM
By default, Session is disabled for WebService.

It works during DirectEvent, because, we think, a WebMethod is called from the page context.

Please set up the following attribute for WebMethod.

[WebMethod(EnableSession = true)]

Feb 02, 2012, 5:01 PM
Here is the good article about using Session in WebService.

Feb 02, 2012, 5:24 PM
Daniil, you're the guy!!!

I am very grateful for your help!
Thanks a lot!