Partial Classes in C#

Question

Are there are good uses of Partial Classes outside the webforms/winforms generated code scenarios? Or is this feature basically to support that?

Answer 1

I just found a use for partial classes. I have a [DataContract] class that I use to pass data to the client. I wanted the client to be able to display the class in a specific way (text output). so I created a partial class and overrode the ToString method.

Answer 2

Code generation was the driving force behind partial classes. The need comes from having a code-generated class that is constantly changing, but allow developers to supply custom code as part of the class that will not be overridden everytime changes are made that force the class to be regenerated.

Take WinForms or Typed-DataSets for example (or any designer for that matter). Everytime you make a change to the designer it serializes the corresponding code to a file. Let's say you need to provide a few additional methods that the generator doesn't know anything about. If you added it to the generated file your changes would be lost the next time it was generated.

A project that I'm currently working on uses code-generation for all the DAL, BLL, and business entities. However, the generator only get's us 75% of the information. The remaining portion has to be hand coded (custom business logic for instance). I can assume that every BLL class has a SelectAll method, so that's easy to generate. However My customer BLL also needs to have a SelectAllByLocation method. I can't put this in my generator because it's not generic to all BLL classes. Therefore I generate all of my classes as partial classes, and then in a separate file I define my custom methods. Now down the road when my structure changes, or I need to regenerate my BLL for some reason, my custom code won't get wiped out.

Answer 3

Where I'm at we have a program that handles incoming files from clients. It's set up so that each client's code is in it's own class library project, which knows how to handle whatever format that client chooses to use.

The main code uses the libraries by defining a fairly extensive interface that a class in the library must implement (probably should be a few distinct interfaces, but it's too late to change it now). Sometimes that involves a lot more code in the same class than we'd normally think prudent. Partial classes allow us to break them up somewhat.

Answer 4

I find partial classes to be extremely helpful. Usually they are used to be able to extend autogenerated classes. I used them in one project with heavy unit tests. My UT classes had complex dependencies and it was not very practical to separate code across multiple classes.Of course it is better to use inheritance\composition but in some cases partial classes can be rally helpful.

Answer 5

maybe its too late but please let me to add my 2 cents too:

*.When working on large projects, spreading a class over separate files allows multiple programmers to work on it simultaneously.

*.You can easily write your code (for extended functionality) for a VS.NET generated class. This will allow you to write the code of your own need without messing with the system generated code

Answer 6

Sometimes you might find terribly old code at work that may make it close to impossible to refactor out into distinct elements without breaking existing code.

When you aren't given the option or the time to create a more genuine architecture, partial classes make it incredibly easy to separate logic where its needed. This allows existing code to continue using the same architecture while you gain a step closer to a more concrete architecture.