ios - 单例不返回任何图像

Question

我正在尝试从 FB 获取个人资料图像并使用单例类保存它，但是当我尝试在 UIImageView 中显示它时它似乎没有保存任何图像。我已经测试了正在获取 facebook 个人资料图像的代码并且它可以正常工作。为什么它不能使用单例工作？

FBSingleton.h

@implementation FBSingleton

static FBSingleton *sharedInstance = nil;

// Get the shared instance and create it if necessary.
+ (FBSingleton *)sharedInstance {
    if (sharedInstance == nil) {
        sharedInstance = [[super allocWithZone:NULL] init];
    }

    return sharedInstance;
}


- (id)init
{
    self = [super init];

    if (self) {
        // Work your initialising magic here as you normally would

        self.userImage = [[UIImage alloc] init];
    }

    return self;
}

@end

FBSingleton.h

@interface FBSingleton : NSObject

@property (nonatomic, strong) UIImage *userImage;

+ (instancetype)sharedInstance;
@end

ViewController.h - 保存 UIImage

    UIImage *theImage = [[FBSingleton sharedInstance] userImage];

    if (!theImage) {
        // download the image from Facebook and then save it into the singleton



        [FBRequestConnection
         startForMeWithCompletionHandler:^(FBRequestConnection *connection, id result, NSError *error) {
             if (!error) {
                 NSString *facebookId = [result objectForKey:@"id"];

             FBSingleton *sharedSingleton = [FBSingleton sharedInstance];

                UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"https://graph.facebook.com/%@/picture?type=large", facebookId ]]]];

                 sharedSingleton.userImage = image;

             }
         }];




    }

AnotherViewController.m - 获取表单单例类

FBSingleton *sharedSingleton = [FBSingleton sharedInstance];
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(tableView.frame.size.width/2-75, 50.0f, 100.0f, 100.0f)];
    [imageView setImage:sharedSingleton.userImage];

    [self.view addSubview:imageView];

Answer 1

你在单例类初始化中错过了@synchronized(self)

FBSingleton *sharedInstance = nil;

// Get the shared instance and create it if necessary.

    + (FBSingleton *)sharedInstance {
        @synchronized(self){
            if (sharedInstance == nil) {
                sharedInstance = [[super allocWithZone:NULL] init];
            }
        }
        return sharedInstance;
    }