方法未返回调用时应返回的内容

Question

I have a piece of code that returns an object of type Card like so:

-(Card*) drawRandomCard {
    if ([self.cards count]) {
        unsigned index = arc4random() % self.cards.count;
        Card *randomCard = self.cards[index];
        [self.cards removeObjectAtIndex:index];
        NSLog(@"%@", randomCard.description);   **//returns a description and not null**
        return randomCard;
    } else {
        NSLog(@"nil");
        return nil;
    }
}

This actually works fine when I use it in other functions, but there is a problem with this one below:

- (IBAction)addCards:(UIButton *)sender {
    int numberOfCardsToAdd = EXTRA_CARDS_NUMBER;

    if ([[self.collectionView visibleCells] count] == 0) {
        numberOfCardsToAdd = self.startingCardCount;
    }

    for (int i = 0; i < numberOfCardsToAdd; i++) {
        if (!self.game.deck.isEmpty){
            Card *cardToAdd = [self.game.deck drawRandomCard];   
            NSLog(@"%@", cardToAdd.description); **// gives (null)**
                if (cardToAdd) {  **// this does not get called**
                    // do stuff with cardToAdd
               }
            }
        }
        [self.collectionView reloadData];
}

So for some reason it seems my drawRandomCard , when called with the method above, does not work. Does anyone know how to fix this?

Thanks very much!

Edit: my method for initializing the game object that has the deck property:

- (id) initWithNumberOfCards: (int) numberOfCards withDeck: (SetsPlayingDeck *) deck {
    self = [self init];
    self.score = 0;
    _deck = deck;
    _cards = [[NSMutableArray alloc] initWithCapacity:numberOfCards];
    for (int i = 0; i < numberOfCards; i++) {
        [_cards addObject: [_deck drawRandomCard]];
    }
    return self;

}

This method is called right at the start of the program.

Edit #2:

Here is the code that initializes the game object, along with a deck object that is its property:

- (SetsGame *) game {
    if (!_game) {
        SetsPlayingDeck *deck = [[SetsPlayingDeck alloc] init];
        _game = [[SetsGame alloc] initWithCardCount:self.startingCardCount usingDeck:deck];
    }

    NSLog(@"%@", _game.deck.description);  **// this returns null!!**
    return _game;
}

Answer 1

As far as I can see, the issue should lie with the method initWithCardCount:usingDeck: , where you probably forgot to assign the deck argument to the deck property (or for some reason the assignment is not executed):

    _game = [[SetsGame alloc] initWithCardCount:self.startingCardCount usingDeck:deck];

So, please review this or post that method definition.

Answer 2

Maybe the problem is that you're running out of cards. Inside your init method you have the following line inside a for-loop:

[_cards addObject: [_deck drawRandomCard]];

And inside your drawRandomCard method you have the following line:

[self.cards removeObjectAtIndex:index];

I'm assuming that _cards (1st line) and self.cards (2nd line) are different objects.

Probably, by the time you call Card *cardToAdd = [self.game.deck drawRandomCard]; inside your addCards: method you don't have any cards left.

Try to set a breakpoint and step in the for-loop and let me know,

Hope this helps!