Incompatible pointer types assigning to 'NSString *' from 'NSMutableArray *'

Question

I'm presently taking an iOS development course and this line of the code I've encountered in the course generates this warning: Incompatible pointer types assigning to 'NSString *' from 'NSMutableArray *'.

media.comments = randomComments;

The array is created in this line:

NSMutableArray *randomComments = [NSMutableArray array];

I tried adding mutableCopy to the end of randomComments array to silence the warning, as suggested elsewhere on this site, but the warning remains:

// Doesn't silence warning    
NSMutableArray *randomComments = [[NSMutableArray array]mutableCopy];

Does anyone have another suggestion how to quell the incompatible pointer type warning I've encountered?

Here is the complete method:

- (void) addRandomData {
    NSMutableArray *randomMediaItems = [NSMutableArray array];

    for (int i = 1; i <= 10; i++) {
        NSString *imageName = [NSString stringWithFormat:@"%d.jpg", i];
        UIImage *image = [UIImage imageNamed:imageName];

        if (image) {
            BLCMedia *media = [[BLCMedia alloc] init];
            media.user = [self randomUser];
            media.image = image;

            NSUInteger commentCount = arc4random_uniform(10);
            NSMutableArray *randomComments = [NSMutableArray array];

            for (int i  = 0; i <= commentCount; i++) {
                BLCComment *randomComment = [self randomComment];
                [randomComments addObject:randomComment];
            }

            media.comments = randomComments;

            [randomMediaItems addObject:media];
        }
    }

    self.mediaItems = randomMediaItems;
}

Answer 1

Your basic problem is trying to assign one object type ( NSMutableArray ) to a different object type ( NSString ). You need to decide which is the correct type and make both objects that type.

Assuming that you're creating an array of objects ( BLCMedia ) each of which has a comments property, of type NSString , the following should fix your issue:

- (void) addRandomData {
    NSMutableArray *randomMediaItems       = [NSMutableArray array];
    for (int i = 1; i < 11; i = i + 1) {
        NSString *imageName                = [NSString stringWithFormat:@"%d.jpg", i];
        UIImage *image                     = [UIImage imageNamed:imageName];
        if (image != nil) {
            BLCMedia *media                = [[BLCMedia alloc] init];
            media.user                     = [self randomUser];
            media.image                    = image;
            NSUInteger commentCount        = arc4random_uniform(10);
            for (int i = 0; i < commentCount; i = i + 1) {
                BLCComment *randomComment  = [self randomComment];
                media.comments             = randomComment;
            }
            [randomMediaItems addObject:media];
        }
    }
    self.mediaItems = randomMediaItems;
}

If, however, a BLCMedia object is intended to have an array of NSString objects as its comments property, the following would fix your issue:

// In BLCMedia.h/.m
// Change this:
@property (copy  , nonatomic) NSString       *randomComments;
// To this:
@property (strong, nonatomic) NSMutableArray *randomComments;


- (void) addRandomData {
    NSMutableArray *randomMediaItems           = [NSMutableArray array];
    for (int i = 1; i < 11; i = i + 1) {
        NSString *imageName                    = [NSString stringWithFormat:@"%d.jpg", i];
        UIImage *image                         = [UIImage imageNamed:imageName];
        if (image != nil) {
            BLCMedia *media                    = [[BLCMedia alloc] init];
            media.user                         = [self randomUser];
            media.image                        = image;
            NSUInteger commentCount            = arc4random_uniform(10);
            NSMutableArray *randomComments     = [NSMutableArray array];
            for (int i = 0; i <= commentCount; i = i + 1) {
                BLCComment *randomComment      = [self randomComment];
                [randomComments addObject:randomComment];
            }
            media.comments = randomComments;
            [randomMediaItems addObject:media];
        }
    }
    self.mediaItems = randomMediaItems;
}