Query on structuring project (Classes v Modules)

Stainless_Steel

Hi all,

I am trying to understand when to use Classes v Modules. I'll use an example to illustrate my problem. Language is VB.NET.

Within my Form class, I have a background worker. The worker is kicked off by a button press. Depending on what is displayed on the form, I need to do a specific job. I determine what the job is and pass this info to the worker as an argument.

The background worker is required to allow a user to still use the form as the processes can be quite time consuming.

So, here is the background worker DoWork event;

Private Sub BackgroundWorker1_DoWork
(ByVal sender As System.Object	ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork

   Select Case e.Argument

        Case "job1"
             ProcessingJob_1()
        Case "job2"
             ProcessingJob_2()
 
   End Select

End Sub

The ProcessingJob_x are subs in a module. The jobs run queries etc and load a public DataTable object.

After this, I need to update the GUI (form) with the DataTable results (I cannot do this in ProcessingJob as that would cause a cross-thread issue). As with ProcessingJob_x, what happens exactly depends on the circumstances. So, similarly to the DoWork event, I use the RunWorkerCompleted event like so;

Private Sub BackgroundWorker1_RunWorkerCompleted(....)

    Select Case yyy

       Case "job1"
           ProcessingJob_1_Post()
       Case "job2"
           ProcessingJob_2_Post()

    End Select

End Sub

As before, ProcessingJob_x_Post() are subs within a module.

So...what is my problem....

I guess it all feels a bit...I dunno...wrong! I am using OOP and I don't quite understand when to use classes to create objects.

I am using modules only and it all seems a bit VB6.

I guess I am looking for guidance from the experts on how yee would accomplish implementing the above concept.

Many thanks for your time.

neil_hosey

Modules are a throwback to VB6 where they were essentially static classes in c#/java/etc...

Like a static class, modules should just be used for helper methods only in my opinion. The main problem with modules is if you depend on them highly to house your core business logic, you break the rule "Open for extension, closed for modification" pretty quickly when new additions to business logic comes along. This is because you can't subclass a module.

The advantage of using a class here for each ProcessingJob is that you could use the Factory method pattern to retrieve which class (have one class for each ProcessingJob_x which inherits from a base IProcessingJob interface)

Then you can use delegates and apply the observer pattern to solve your problem of cross thread communication, see here for an example:
http://www.codeproject.com/Articles/5754/Implementing-Observer-Pattern-in-VB-NET

Stainless_Steel

Just getting back to my thread now.

Thanks for that Neil. To be honest it is a bit over my head...I have a lot of reading to do!

Any other feedback appreciated.