What is the correct system design when dealing with third party API?

Question

This blog post by Joubert just opened my eyes. I have dealt with a lot of design patterns in Java and other languages. But Objective-C is a rather unique language.

Let's say that in a project we talk with a third party API, like Dropbox or Facebook. What I've been doing so far is to combine everything that has to do with the third party API into a singleton class. So I can access the class from anywhere in my view controllers. I can just go for example: [[DropboxModel sharedInstance] uploadFile:aFile]

However as the blog post noted, this isn't efficient and leads to spaghetti code and bad unit testing. So what is the best way to design the system so that it's modular and easy to use?

Answer 1

I would dispute the idea that singletons lead to spaghetti code and are inefficient. However, the unit testing problem is legitimate and singletons do reduce modularity since they are really just fancy global variables.

I like Joubert's idea of injecting the singleton instance into the controller(s) from the app delegate (which is itself a singleton, ahem). I think the same approach would work for you.

What I normally do in these situations where I might want to use a different stub object in unit tests is define a protocol to represent the API and make my "real" API object conform to it and also my stub API object. I use the stub in the unit tests and the real object in the app.