How to modify an NSMutableDictionary using setValue or setObject?

Question

In the header file:

@property (strong, nonatomic) NSMutableArray *vocabs;
@property (strong, nonatomic) NSMutableDictionary *vocab;

in the .m file:

-(void) loadFile {
    NSString* filepath = [[NSBundle mainBundle]pathForResource:@"vocabs" ofType:@"json"];

    NSData *data = [NSData dataWithContentsOfFile:filepath];

    vocabs = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];



}

-(void) renderVocabs {
    //NSLog(@"json file = %@", vocabs);
    if ([vocabs count] == 0) {

    } else {

        vocab =  [vocabs objectAtIndex:vocabIndex];
        //NSLog(@"%d", vocabIndex);
        //NSLog(@"%d", [vocabs count]);
        NSString *word = [vocab objectForKey:@"word"];

        labelWord.text = word;

        tvDefinitions.text = [NSString stringWithFormat:@"(%@) %@" , [vocab objectForKey:@"subject"], [vocab objectForKey:@"definitions"]];

        NSString *imgName = [NSString stringWithFormat:@"%@.jpg",word];
        NSLog(@"%@", imgName);
        [imageVocab setImage: [UIImage imageNamed:imgName]];

        NSString *remembered = [vocab objectForKey:@"remembered"];

        if ([remembered isEqualToString:@"0"]) {

            self.btnRemember.hidden = FALSE;

        } else {

            self.btnRemember.hidden = TRUE;

        }

    [self setDisplayFontSize];

    }
}
- (IBAction)btnTick:(UIButton *)sender {
    [vocab setObject:@"1" forKey:@"remembered"];
}

and I got

** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object'
*** First throw call stack:

What did I do wrong? Can anyone point me to the right direction? Thanks in advance.

Answer 1

Your array most likely contains only NSDictionary instances, not NSMutableDictionary instances, therefore you can't modify them. If you send NSJSONReadingMutableContainers to your JSONObjectWithDataCall you should get back mutable objects.

self.vocabs = [NSJSONSerialization JSONObjectWithData:data options: NSJSONReadingMutableContainers error:nil];

Answer 2

The problem is that calling something an NSMutableDictionary (or array) doesn't make it one.

Basically this code is irrelevant:

@property (strong, nonatomic) NSMutableArray *vocabs;
@property (strong, nonatomic) NSMutableDictionary *vocab;

What matters is what object you assigned to those properties.

Answer 3

This line...

vocab =  [vocabs objectAtIndex:vocabIndex];

Needs to be...

self.vocab = [NSMutableDictionary dictionaryWithDictionary:[vocabs objectAtIndex:vocabIndex]];