Vb.net - using session variables set to objects

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Hi all,

I am trying to set and retrieve session variables. These are actually a memorystream and stream writer.

I set them in global.aspx thus -

VB.NET

Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
    Dim memoryStream As New System.IO.MemoryStream()
    Dim textWriter As System.IO.TextWriter = New System.IO.StreamWriter(memoryStream)
    Dim bytesInStream As Byte()
End Sub

this seems to work. No errors anyway.

What I have tried:

In an in a function in an aspx.vb page I call on those session variables -

Session("textWriter").WriteLine("test")

No errors on preview, but when I run it, it throws the exception - "Object variable or With block variable not set."

It's not within a loop or with block, so I guess it's not seeing the Session Variable ???? But only when you run the code? As I said, it's not showing up as an error in the code itself.

Really stuck, any ideas? Or for that matter, how I could set these objects once even on another .aspx page_load sub and be able to see them in a function in a different .aspx page?

I can't set them in the page that the function resides because the aspx.vb page loads many times when client AJAX calls it and it has to keep appending to the memorystream.

Posted 3-Aug-16 8:43am

Member 12637386

Updated 3-Aug-16 10:28am

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jkirkerx 3-Aug-16 15:56pm

WriteLine? WriteLine to where? to write a line on the webpage, the text has to be in the response output of HTML like Response.Write("Text")

What are you trying to store, like an image?

Member 12637386 3-Aug-16 16:00pm

The writeline writes text to a memory stream that I will later download as a text file. See the code above in the application_start block (which should actually be session_start)

Dim memoryStream As New System.IO.MemoryStream()
Dim textWriter As System.IO.TextWriter = New System.IO.StreamWriter(memoryStream)

jkirkerx 3-Aug-16 16:14pm

Yeah but a session is an object that the web server controls, and is just a string or primitive object. Asp.net provides access to the session on the web server called Session.

You may be able to save a base64 string of bytes in the session. Make a byte array and convert it to a base64 string and vice versus.

2 solutions

Solution 2

In Global.asax, I know you can set a property, like the one when you right click the project, and then click on the resource tab, in which you can set a string resource. But it's not a Session object. It's a reflection Object.

I also know that you can write to the resource or create new ones as well, but my VS2015 is malfunctioning at the moment, and I can't show an example of it.

protected void Application_Start()
{
     AreaRegistration.RegisterAllAreas();
     FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
     RouteConfig.RegisterRoutes(RouteTable.Routes);                     
}

public static string GetWebsiteName()
{
    string pValue = Properties.Settings.Default.WebsiteName;
    return pValue;
}

To access the string, MvcApplication is the class of the Project, not sure what yours will be.

string websiteName = MvcApplication.GetWebsiteName();

Posted 3-Aug-16 10:28am

jkirkerx

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Richard Deeming · Accepted Answer · 2016-08-03T10:08:00

Solution 1

You have created three local variables in the Application_Start method, but you haven't stored them anywhere. You certainly haven't added them to the session.

To store the variable in the session, you need to add it to the session. To do that, you would need to use the Session_OnStart event:

C#

Sub Session_OnStart(ByVal sender As Object, ByVal e As EventArgs)
    Dim memoryStream As New System.IO.MemoryStream()
    HttpContext.Current.Session.Add("memoryStream", memoryStream)
    
    Dim textWriter As New System.IO.StreamWriter(memoryStream)
    HttpContext.Current.Session.Add("textWriter", textWriter)
End Sub

You can't use Application_Start, because that only fires once when your application starts up. The Session_OnStart event[^] fires when a new session is created, which will happen multiple times whilst your application is running, as different users connect to it.

ASP.NET Application Life Cycle Overview[^]

Posted 3-Aug-16 10:08am

Richard Deeming

Updated 3-Aug-16 10:26am

v2

Comments

Member 12637386 3-Aug-16 16:24pm

Richard,

I added -

Sub Session_OnStart(ByVal sender As Object, ByVal e As EventArgs)
Dim memoryStream As New System.IO.MemoryStream()
HttpContext.Current.Session.Add("memoryStream", memoryStream)

Dim textWriter As New System.IO.TextWriter(memoryStream)
HttpContext.Current.Session.Add("textWriter", textWriter)
End Sub

New System.IO.TextWriter(memoryStream) shows an error - 'New cannot be declared on a class that is declared MustInherit

It appears that Session("memoryStream") is available across the session though. Thanks

Richard Deeming 3-Aug-16 16:26pm

Sorry, that should be StreamWriter, not TextWriter. I've updated the answer.

Member 12637386 3-Aug-16 16:41pm

Ahh. Got it. thanks again

Member 12637386 3-Aug-16 16:33pm

And if I remove the 'New' the error is now at memoryStream in the line -
Dim textWriter As System.IO.TextWriter(memoryStream)

Error reads - Array bounds cannot appear in type separators.

Member 12637386 3-Aug-16 16:39pm

I got it. I changed it to -
Dim textWriter As System.IO.TextWriter = New System.IO.StreamWriter(memoryStream)

Going to accept your answer Richard. it helped a lot. Thanks

jkirkerx 3-Aug-16 17:00pm

I didn't know there was a Session_OnStart event.
Plus I thought only primitives could be stored in a session. hmm
Good job Richard!

Richard Deeming 4-Aug-16 7:56am

If you're using one of the out-of-process session state modes, then the types you store have to be serializable. But for the default in-process mode, you can store (almost) any type in the session.

jkirkerx 4-Aug-16 13:12pm

Thanks Richard!
Say I have question or just curious about a formula I'm working on that I would like to run by yo choose to entertain the question or formula, could you pm me? if not that's cool

Richard Deeming 4-Aug-16 13:46pm

Wouldn't it be better to post it as a question? That way, other people can help too. :)

jkirkerx 4-Aug-16 14:45pm

Alright