Help in Converting Desktop App to Web App.

QuickBooksDev

I need some help with the fundamentals. I have a VB.Net Desktop app that I am converting to a Web App. I do not understand how the variable are stored/saved, etc. Can something walk me through this? The structure is the following: 1. Visual Studio 2013 2. Startup main page is a C# module. This does screen / view handling and OAuth authentication. 3. It references a class that is written in VB.2013 (this has the main business logic). Call this vbMain. 4. The VB.2013 class invokes another VB.2013 class (call it vbServHandler. This 2nd VB class handles all the real interface to the web services (REST) that was authenticated in the C# module. It seem that the variable in the 1st VB Class (vbMain) are not preserved across requests but those in the 2nd VB class are. I just do not understand this. Can somesome please give me some?

jkirkerx

The best I can do here is this, perhaps someone else can explain it better, but looks like there are no takers on this post. A windows app, is really different. Within a windows app, you have access to so many resources, and can make global buffers, that can be used from form or dialog to form or dialog. A web page, is a 1 time deal. you create the web page, and when done, or the page is unloaded, everything dies with it. When you create another page, you start all over again, and the process repeats. There are ways to store information from page to page, or transfer information from page to page, but that's provided by the web server or through the use of hyperlink query strings. [Sort of an Anwser] Some of the code is reusable, the rest just supports the windows controls and objects. You really need to start from scratch, and design a web based system with the UI first. Now write the navigation part, 1 page to the other, make it look pretty, then start plugging in your logic from the other program, 1 piece at a time until it works correctly. Sounds to me like you have very little experience at building a web application, and mid level experience at building a windows application. It's important to understand the different between the 2 before you try to port the windows app to a web app. There's no magic or easy way to do it.

QuickBooksDev

Thanks I understand that there is no magic and no converter and that each page is new and any variables should be as initialized when built or saved in either viewState, SessionState, ApplicationState a cookie or other external source. This does not explain why variables in the 2nd VB class (vbServHandler) has new data in it while the 1st (vbMain) does not. What would cause this?

Richard Deeming

It sounds like vbServHandler is using Shared fields. You should generally avoid Shared fields in ASP.NET applications unless you really know what you're doing. For example, the data in the fields will be shared across all requests from all users, which means you could easily end up showing data meant for user A to user B by mistake.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

QuickBooksDev

They are NOT shared. I think it may be when a button control is hit on the page that the vbServHander is not getting re-initialized (vbServHandler variables still have data). I have done this: 1. By just click in the upload button on the vbMain button multiple times. 2. Clicking on the C# menu button (Upload) to reload the page. 3. Going back to the main page and clicking on the Upload button to reload the upload page. 4. Even refreshing the main home page via F5. In all cases the constructor for vbMain (i.e. sub new) shows data in the vbServHandler variables. I am programming around this (I actually think it is better) but just do not understand it.

Richard Deeming

If the variables are persisted between requests to your site, and they're not stored in application or session state, then either they're stored in Shared fields, or the instance of the containing class is stored in a Shared field somewhere.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

QuickBooksDev

They are not saved anywhere. If they are in some shared object then I do not know where it could be. Here is the definition of the object I was checking in the Sub new of vbMain. Public AccountCollection As Collection in what I was calling vbServHandler. Real name is QBAPIV3Cl which is part of DLL QBAPIV3VS2013. This is invoked via by vbMain Imports QBOAPIV3VS2013 . . Public aQB As New QBOAPIV3VS2013.QBAPIV3Cl() which is defined in a module within vbMain. . . Which is referenced by the C# Web App using vbMainDLL; In the C# program it is defined as vbMainDLL.vbMain vbMain; vbMain = new vbMain(TheRealmID,TheAccessToken,TheAccessTokenSecret, TheConsumerKey,TheConsumerSecret, TheContext,TheDataService, pOutReason: ref pOutReason); The Sub New for vbMain has aQB.accountcollection.count Referenced object has a value of nothing the first time. then 121 every other time. I would expect a value of nothing each time. The c# program has no references to the aQB class/QBOAPIV3VS2013.QBAPIV3Cl. So what am I missing?

Richard Deeming

QuickBooksDev wrote:

which is defined in a module within vbMain.

A Module is effectively a class in which every member is Shared. If your fields are stored in a Module, they they're Shared by definition.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

QuickBooksDev

Here is the class Public Class QBAPIV3Cl ... No Module Public AccountCollection As Collection AccountCollection is the variable that I am checking for persistence. It is references by the vbMain module as Module Common which is a separate vb source file. Module Common .. Public aCL As New vbMain.QBAPIV3Cl() So what you are saying since MODULE common is a MODULE everything in it is Shared/Static including all of aCL????

Richard Deeming

QuickBooksDev wrote:

So what you are saying since MODULE common is a MODULE everything in it is Shared/Static including all of aCL????

Yes, that's correct.

Module Statement[^]:

A module has the same lifetime as your program. Because its members are all Shared, they also have lifetimes equal to that of the program. ... All members of a module are implicitly Shared.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

QuickBooksDev

So for a web app it last forever??? Is there a way of making a module non-Shared so I do not have to re-organize the program? Or what is the best way to have the module non-Shared?

Richard Deeming

Yes, in a web application it will last until the AppPool recycles. There's no way to make a module non-shared. However, you might be able to get away with changing the field to a property, and adding code to retrieve the value from the current session if the code is running in an ASP.NET application. Something like this should work:

Imports System.Web
Imports System.Web.Hosting

Module Common
' The key for the field in the session - this must be unique:
Private Const SessionKey As String = "Common::aCL"

' Backing field used for non-web applications:
Private aCLNonWeb As vbMain.QBAPIV3Cl

Public ReadOnly Property aCL() As vbMain.QBAPIV3Cl
    Get
        If Not HostingEnvironment.IsHosted Then
            ' Not running in ASP.NET:
            If aCLNonWeb Is Nothing Then
                Set aCLNonWeb = New vbMain.QBAPIV3Cl()
            End If
            
            Return aCLNonWeb
        End If
        
        Dim context As HttpContext = HttpContext.Current
        If context Is Nothing Then
            Throw New InvalidOperationException("No current request.")
        End If
        
        Dim value As vbMain.QBAPIV3Cl = DirectCast(context.Session(SessionKey), vbMain.QBAPIV3Cl)
        If value Is Nothing Then
            value = New vbMain.QBAPIV3Cl()
            context.Session.Add(SessionKey, value)
        End If
        
        Return value
    End Get
End Property

End Module

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

QuickBooksDev

Thanks will give it a try.