如何將UIImage添加到NSMutableArray

Question

我正在嘗試使用以下代碼將來自Web服務的UIImage添加到我的NSMutableArray中：

for (int i=0; i<[totalRowCountString intValue]; i++)
{    
    NSString *criticsRatingString = [[JSON valueForKeyPath:@"movies.ratings.critics_rating"] componentsJoinedByString:@" "];
    NSLog(@"criticsRatingString: %@", criticsRatingString);

    if ([criticsRatingString isEqualToString:@"Certified Fresh"])
    {
        self.ratingImage = [UIImage imageNamed:@"rt_certified_fresh.png"];
    }
    else if ([criticsRatingString isEqualToString:@"Fresh"])
    {
        self.ratingImage = [UIImage imageNamed:@"rt_fresh.png"];
    }
    else if ([criticsRatingString isEqualToString:@"Rotten"])
    {
        self.ratingImage = [UIImage imageNamed:@"rt_rotten.png"];
    }
    else if ([criticsRatingString isEqualToString:@"Spilled"])
    {
        self.ratingImage = [UIImage imageNamed:@"rt_spilled.png"];
    }
    else if ([criticsRatingString isEqualToString:@"Upright"])
    {
        self.ratingImage = [UIImage imageNamed:@"rt_upright.png"];
    }

    [tomatorRatingImages addObject:self.ratingImage];
    NSLog(@"tomatoRatingImages: %@", tomatorRatingImages);
}

但是我的NSLog for TomatoRatingImages返回NULL。 任何想法為什么它返回NULL？

更新：我的NSMutableArray已在我的viewWillAppear方法中初始化。

Answer 1

您必須先初始化數組，然后才能向其中添加對象。

NSMutableArray *tomatorRatingImages = [[NSMutableArray alloc] init];

Answer 2

NSMutableArray * tomatorRatingImages =[[NSMutableArray alloc]init];

[tomatorRatingImages  addObject:[UIImage imageNamed:@"rt_spilled.png"]];

[tomatorRatingImages  addObject:[UIImage imageNamed:@"rt_spilled1.png"]];

[tomatorRatingImages  addObject:[UIImage imageNamed:@"rt_spilled2.png"]];

您可以在NSMutableArray中輸入多個圖像。

Answer 3

像這樣初始化

NSMutableArray * tomatorRatingImages =[[NSMutableArray alloc]initWithCapacity:3];

Answer 4

如果您具有NSMutableArray實例的屬性，則最好編寫getter對其進行初始化。 它只負責初始化變量，也僅在需要時才加載。

   -(NSMutableArray *) tomatorRatingImages {
         if(_tomatorRatingImages == nil) {
               _tomatorRatingImages = [NSMutableArray alloc] init];
         }
         return _tomatorRatingImages;
    }