Objective-C Gotchas


You’re working in Objective-C land trying to get a product out the door and into the Apple iTunes Store, right? (Don’t argue with me I’m just setting the stage.) You’re feeling the second cup of coffee seep into your bloodstream which creates a certain euphoric sensation as the last 3 times you mashed Cmd+B turned up no errors. Yes, that’s what’s happening in your copy of XCode right now. You then Cmd+Tilde to toggle the other XCode window active (Cmd+Tilde is a nifty Apple shortcut for switching active windows in the current app) and Cmd+B once again when a red flag on the play pops up in some code that had been just fine moments ago? What happened? Hi, I’m Cliff. You’re here because XCode got’cha and you’re not quite sure how/why/where. I’m here because I wanna list as many of these got’chas before I forget them.

Property accessor notation in Earlier SDKs
Here’s one weird gotcha that I just hit again for the first time. If you have a variable typed as a protocol and that protocol has a setter, which takes another protocol type defined then you may get an error when using dot notation in SDKs earlier than 3.0. That is a definition like this:

@protocol MyCoolAbstractType <NSObject>
-(void) setNetworkDataProvider:(id<MyNetworkDataProvider>)aNetworkDataProvider;
@end

…should be coded like this:

@protocol MyCoolAbstractType <NSObject>
@property (nonatomic, retain) id<MyNetworkDataProvider> networkDataProvider;
@end

…before you can do this:

id<MyCoolAbstractType> myObj = //create object from factory
myObj.networkDataProvider = [[MyConcreteNetworkDataProvider alloc] init];

Evidently the “Discover setter is a property” feature is something new Santa delivered with 3.0 and never told me about. Here I thought I had that toy from 2 years ago!

Unit Tests Can’t Be Signed
I added a unit test dependency to my “Application” target the other week in order to streamline my dev cycles. The idea was to ensure any changes I made to satisfy the integrated application bundle did not impact behaviors outlined in my test cases. (I use mini applications to perform my integration testing.) The problem here is that, even though this works well for simulator builds, an on-device build will fail as XCode attempts to sign your unit test target output. I haven’t discovered a work-around for this one yet so I’m gonna just punt and remove the test dependency from any targets meant to run on device.

I’ll trow up more as I find them…

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