VB.NET Beginner design question

VB.NET, VS 2010, .NET 4

Hello,

I've written an application. I've discovered that it is full of circular references. I would like to rewrite portions of my code to improve its design. I have read about tiered programming and want to implement something like it for my application.

Background: My application is a control program for an industrial machine. It parses a recipe (from an Excel file) which contains timing information and setpoints for the various attached devices. There are three main types of devices: Most are connected through Beckhoff terminals and communicate via TwinCAT (Beckhoff's pseudo-PLC software) and two are RS-232 devices, each with a different communication protocol. I can c开发者_开发知识库ommunicate with the Beckhoff devices via a .NET API provided by Beckhoff. I have written parser classes for the two RS-232 devices. Some of the Beckhoff devices are inputs, some are outputs; some are digital, some are (pseudo-)analog.

I think my problem is that I was trying to wrap my head around OOP while writing the application so I created classes willy-nilly without a clear idea of their hierarchy. At some points, I tried to do what I thought was right by, say, making a "Device" class which was inherited by, say, a "TwinCatDevice" class and a "Rs232Device" class. But then I just stuffed all of the communication code in those classes.

What I'm trying now is creating some communication modules (e.g., UtilTwinCat, UtilRs232) that contain abstract methods like "Connect", "Disconnect", "Read", "Write", etc. Then I'm trying to rewrite my "Device" class and subclasses to use these modules so they don't have to contain any of the (sometimes redundant) communication code.

Here's my question: Would it be good design to create separate classes for each type of communication type? i.e., should I have, say, "TwinCatReadOnlyDigital", "TwinCatReadOnlyAnalog", "TwinCatWriteOnlyDigital", "TwinCatWriteOnlyAnalog", "TwinCatReadWriteDigital", "TwinCatReadWriteAnalog", "Rs232ReadOnlyDigital", etc? Or perhaps some interfaces like IReadOnly, IWriteOnly, IDuplex?

This seems like it can't be the right approach in that I imagine someone who is good at programming wouldn't end up with a billion different classes for every eventuality. Is there some way I could selectively implement an interface on a class at run time? I think that's a stupid question... I'm still trying to wrap my head around why one would use an interface. I'm looking for some basic insight on how to grapple with this type of design problem. Specifically, if you have a lot of "things" that differ slightly, is the best approach to create lots of classes that differ slightly?

Thanks a lot in advance, Brian

Edit: I just wanted to add, to be clear, there is a finite number of devices whose parameters are known, so it would be straightforward to write classes for all the types I'd need. I just wonder if there's a better approach.

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That's not really enough information for any concrete answers, but let me make a few suggestions.

"I'm still trying to wrap my head around why one would use an interface."

Mainly because then you can "program to the interface", that is you needn't care if you're working with a Beckhoff or an RS-232 device - you only care that you can send data to it. Just to make it clear: interfaces don't contain implementations. Classes implementing an interface promise to provide concrete implementations for the functions of the interface.

• Instead of IReadOnly, IWriteOnly and IDuplex use two interfaces: IWriteable and IReadable (or whatever names make sense). Duplex classes will implement both interfaces.
• The Strategy or more likely the Template method patterns may help you with the slightly different classes. Maybe even simple subclassing, but keep in mind that there's often a simpler, nicer solution.
• Don't repeat yourself (DRY): try to find one and only one place for every piece of logic.
• Functionality shared by several classes should reside in a superclass or utility classes.

Also, more concrete questions will result in more concrete answers :)