從“ NSMutableArray *”分配給“ NSString *”的指針類型不兼容

Question

我目前正在上一個iOS開發課程，並且在課程中遇到的這一行代碼會產生以下警告：不兼容的指針類型從'NSMutableArray *'分配給'NSString *'。

media.comments = randomComments;

在此行中創建數組：

NSMutableArray *randomComments = [NSMutableArray array];

我嘗試將mutableCopy添加到randomComments數組的末尾以使警告靜音，如本網站上其他地方所建議的那樣，但警告仍然存在：

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

有人有其他建議如何平息我遇到的不兼容的指針類型警告嗎？

這是完整的方法：

- (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

您的基本問題是嘗試將一種對象類型（ NSMutableArray ）分配給另一種對象類型（ NSString ）。 您需要確定哪個是正確的類型，然后使兩個對象都鍵入該類型。

假設您要創建一個對象數組（ BLCMedia ），每個對象都有一個NSString類型的comments屬性，則以下內容將解決您的問題：

- (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;
}

但是，如果一個BLCMedia 對象預期有一個陣列NSString對象作為它的comments屬性，下面將解決您的問題：

// 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;
}