CODEWITHSUNDEEP
objective-crestasynchronouswrappersynchronous
RyanM
RyanM

Reputation: 4584

How to write an Objective-C REST API wrapper

I’m working of writing an Objective-C wrapper for a REST API. A lot of what I’m reading says not to use synchronous NSUrlConnection requests to avoid blocking the main thread. This makes sense, but I am wondering, what is the best way to make an API wrapper in Objective-C?

For example, we have an API method that takes a session ID and returns whether or not the session is valid. Ideally the wrapper method prototype would look like the following:

- (BOOL) sessionIsValid:(NSString *)sessionId;

So, that method could be called and the return value could be used to decide what to do next. But how would this work if the API call is asynchronous? It seems like the caller would need to set itself as the wrapper's delegate, make a request, and then process the response from the delegate method. Seems pretty ugly for such a simple API call. Is there a good way to achieve this?

Upvotes: 1

Views: 552

Answers (2)

CouchDeveloper
CouchDeveloper

Reputation: 19098

Whether a session is valid or expired, should be an implementation detail of the underlying network layer. Thus, you would rarely have this method in a Objective-C API. Rather you would have an API that looks more like this:

typedef void (^completion_t)(id result, NSError* error);

- (void) fetchAllPostsWithUser:(ID)userID completion:(completion_t)completionHandler;

This is an asynchronous method. The call-site will be notified about the completion through calling the completion handler, which passes the result of the operation and possibly an error object. What result is actually, is entirely up to you: it may be an NSArray of custom objects of class Post or it may be JSON (either serialized or as objects), or whatever. In any case it must be clearly defined in the documentation.

Your "session problem" is part of the authentication scheme. In many cases, NSURLSession, respectively NSURLConnection can already handle authentication completely transparent for you. If not, there are a few delegate methods which can be overridden where you can tailor the behavior. A client (a developer using this API as a library) of that Objective-C API should never be concerned with such "abstract" and "obscure" notions like "session". He/she, knows just passwords, users, posts, etc. ;)

Upvotes: 1

Wain
Wain

Reputation: 119031

If you wanted to return a BOOL you would need to have already setup the session and cached the validity (expiry date) - which isn't always going to be possible. A delegate pattern is a good option. Don't forget that you can implement the delegate pattern using blocks (which give you the option of having multiple different delegates all using the API at the same time).

Upvotes: 0

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