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List object in session C# .NET 3.5

I'm new to .NET but not to web app development. I'm going to ask a question about how I am trying to do something. If you could, please help me answer that question - even if there is a better way to do what I'm doing. It will accomplish what I need and help to educate me.

Then if there's a better way, I'm all ears :) But as I'm still learning, even learning it the non-optimal way will benefit me.

It's a rather simple problem. I'm using MVC and in my controllers I want to be able to add feedback messages to an object in Session. Then I have a shared view which I'm including in the views I want to render the messages to the user. So the flow is like this:

- In global, at startup, I create a new List<string> object and put it in Session:
List<string> messageList = new List<string>();
Session["messages"] = messageList;

- Run the site
- Call to controller
- Controller does its thing (say... delete a database record)
- Controller puts "X Deleted Successfully" into a List<string> object in session:
((List<string>)Session["messages"]).Add("You succesfully deleted record " + id);

- Controller redirects to view
- View includes the shared MessageProcessor view (control)
- MessageProcessor tries to grab the list object from session, check if there are messages, and if yes... render them.
<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
<%
// Get the messages array from the session object.
List<string> messageList = (List<string>)Session["messages"];
if (messageList.Count() > 0)
{
// Process messages by displaying them
foreach(var message in messageList)
{
Response.Write("<li>" + message);
}
}
%>
</asp:Content>

I'm getting the following exception:

Exception Details: System.ArgumentNullException: Value cannot be null.
Parameter name: source

Source Error:

Line 5: // Get the messages array from the session object.
Line 6: List<string> messageList = (List<string>)Session["messages"];
Line 7: if (messageList.Count() > 0)
Line 8: {
Line 9: // Process messages by displaying them

Which says to me, the object is not coming out of session correctly. Is my Line 6 code to pull out the object from session fubared in some subtle way?

Thanks for any help!

// In global:

List<string> messageList = new List<string>();
Session["messages"] = messageList;

// In controller:
((List<string>)Session["messages"]).Add("You succesfully deleted record " + id);

// In control (shared view)
<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
<%
    // Get the messages array from the session object.
    List<string> messageList = (List<string>)Session["messages"];
    if (messageList.Count() > 0)
    {
        // Process messages by displaying them
        foreach(var message in messageList)
        {
            Response.Write("<li>" + message);
        }
    }
 %>	
</asp:Content>

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Bob Learned

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Ayman Aboualnour

you can use the debugger to get what is stored in session object also followup the calling of your code in the session startup.
List<string> messageList = new List<string>();
Session["messages"] = messageList;

you should close the browser after every trial to remove the session

SOLUTION

Ayman Aboualnour

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trippy1976

ASKER

I know how to use a debugger ;)

Anyway, what turned out to be the issue was I tried to initialize the session variable in the Application_Start() method. At this point there is apparently no session. You can add a Session_Start() method into the global file and initialize any session variables there instead and *then* it all works dandy. Thanks for the help everyone.