Xcode project works in Simulator, not on device

Question

Still working on my flash card-themed app. Completely baffled. Lots of possibly salient info.

I have a version which works flawlessly, both in simulator and on multiple devices. But, I made a mistake when submitting to the App Store (wrong Bundle ID and Name), so I created a new project and copied and pasted the code and storyboard. (I didn't just move the files; I recreated them and copied the code.)

First problem was that it wouldn't build because "duplicate symbol _answers in" RootViewController.o and DescendantViewController.o. And there were 3 such duplicate symbols.

Yes, I have declared NSMutableArray *answers in the implementation of both my RootVC and DescedantVC, so I concede that's suspect, except.... it's the exact same code as in the version that works.

Nevertheless, I saw an opportunity to clean up my code, so I created a @property (weak, nonatomic) NSMutableArray *answers in my RootVC and changed the code in the root and descendant View Controllers to reference self.answers . It compiles without any problems.

It runs in the simulator perfectly. As I've just copied the entire code base to a new project, I test everything - no problems. I'm very excited, so I do all the steps to submit to the App Store, except the last one "Submit for Review."

I want to show off to my friend, so I attach my iPhone 6, compile it, run it and when I select "Play" - crash!

The following line is the culprit.

answers = [self pickWrongAnswersIgnoringCard:questionCard];

Both in the simulator and on the device, the last line of the this method is:

return wrongAnswers;

In both cases, wrongAnswers is an array with 3 items.

In the simulator, answers also has 3 items. On my iPhone, answers is nil.

Does anyone have any idea what this could be? The only thing I can think of is that I created the project that works over a year ago and the one that fails today, so maybe some of the Apple settings in the two projects are different? Otherwise, I'm stumped.

Edit

The function, as requested:

-(NSMutableArray *)pickWrongAnswersIgnoringCard:(FlashCard *)questionCard {
  NSMutableArray *wrongAnswers = [[NSMutableArray alloc] init];

  FlashCard *randomCard;

  for (int i=1; i<4; i++) {
    do {
      randomCard = [self pickARandomCardFromDeck:wrongAnswersSource];
    } while ([randomCard.name isEqualToString:questionCard.name] || [wrongAnswers containsObject:randomCard]);
    
    [wrongAnswers addObject:randomCard];
  }

  return wrongAnswers; // device or simulator, wrongAnswers.count = 3
}

Answer 1

I figured it out, even if I don't fully understand.

I changed from @property (weak, nonatomic) to @property (strong, nonatomic) .

That solved it for me.

Works on both simulator and device now.