Question

I’m developing an iOS 4 application.

I have a class with a NSMutableDictionary property:

@interface CardHelper : NSObject <NSXMLParserDelegate>{
    ...

    NSMutableDictionary* cards;

    ...
}

@property (nonatomic, readonly) NSMutableDictionary* cards;

- (id)initWithXMLFile:(NSString *)xmlFileName andLanguage:(NSString *)language;
...

I create that NSMutableDictionary here:

...
#define kNumCards 22
...

- (id)initWithXMLFile:(NSString *)xmlFileName andLanguage:(NSString *)language
{
    if (self = [super init])
    {
        userLanguage = [NSString stringWithString:language];

        cards = [NSMutableDictionary dictionaryWithCapacity: kNumCards];

        [self parseXMLFile:[self GetResourcePathFor:xmlFileName OfType:@"xml"]];

        return self;
    }
    else
        return nil;
}

And I add elements on it here:

- (void) parser:(NSXMLParser *)parser
  didEndElement:(NSString *)elementName
   namespaceURI:(NSString *)namespaceURI
  qualifiedName:(NSString *)qName
{
    NSLog(@"DidEndElement: %@", elementName);
    if ([elementName isEqualToString:@"card"])
    {
        [cards setObject:currentCard forKey:currentCard.Number];
        [currentCard release];
        currentCard = nil;

        return;
    }

    ...
}

CardHelper object is created on a class called ViewController (the main view controller for my app). From this view controller I show another one:

- (IBAction)oneCardCliked:(id)sender
{
    oneViewController = [[OneCardViewController alloc] init];
    oneViewController.cardHelper = cardHelper;

    [self presentModalViewController:oneViewController animated:YES];
}

CardHelper defined in ViewController:

@interface ViewController : UIViewController {
    ...
    CardHelper* cardHelper;
    ...
}
...

I pass cardHelper to OneCardViewController to use there.

But, on OneCardViewController I try to get a card from cards, I get that cards has converted from NSMutableDictionary to NSCFString.

OneCardViewController interface:

@interface OneCardViewController : UIViewController {
    CardHelper* cardHelper;
    ...
}

@property (nonatomic, retain) CardHelper* cardHelper;

I get the exception here:

- (void) setUpTarotGame
{
    int arcaneNumber;
    arcaneNumber = [cardHelper GenerateArcaneNumber];
    NSString* number = [NSString stringWithFormat:@"%d", arcaneNumber];
    if (cardHelper == nil) {
        NSLog(@"cardHelper nil");
        return;
    }
    if (cardHelper.cards == nil)
    {
        NSLog(@"cards nil");
        return;
    }
    else
        NSLog(@"cards count = %d", [cardHelper.cards count]);
    currentCard = [cardHelper.cards objectForKey:number];

    [self setCardImageWithArcane:arcaneNumber];
}

The exception is thrown in this line:

currentCard = [cardHelper.cards objectForKey:number];

Do you know why?

Answer 1

It’s not being converted, it’s being dealloced and the memory is being used for something else.

In your init method you are not retaining these objects :

userLanguage = [NSString stringWithString:language];
cards = [NSMutableDictionary dictionaryWithCapacity: kNumCards];

Try

userLanguage = [language copy];
cards = [NSMutableDictionary alloc] initWithCapacity:kNumCards];

instead.