为什么这个 UIViewController 在调用 twitter 后没有更新？

Question

我正在尝试构建一个基本的 twitter 客户端作为学习 iOS 开发的练习。到目前为止，我有一个 TabBarController，其中一个选项卡是用户的时间线（工作正常），而这个新选项卡用于用户的个人资料。 twitter 调用下面的大部分结构来自一个在线教程，使用 XCode 5 和 twitter API 1.1 获取用户的时间线。然后我对其进行了修改以在第二个 ViewController 中获取用户的个人资料。在此个人资料视图中，我有一个 UIImageView 用于用户的个人资料图片，并有一个标签表示关注者的数量。

当我第一次点击此选项卡以查看个人资料视图时，imageView 为空白。当我第二次单击另一个选项卡，然后单击此配置文件选项卡时，将加载配置文件图像。关注者标签永远不会更新，但是当我调试它时，我可以看到我正确获取了 numFollowers 值。

那么为什么profileImageView在视图的初始视图上没有更新，为什么numFollowers标签从来没有更新呢？

ViewController的相关位：

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    [self twitterProfile];
}

-(void) twitterProfile {
    ACAccountStore *account = [[ACAccountStore alloc] init];

    // Asks for the Twitter accounts configured on the device

    ACAccountType *accountType = [account accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierTwitter];

    [account requestAccessToAccountsWithType:accountType options:nil completion:^(BOOL granted, NSError *error)
     {
         // if we have access to the Twitter accounts configured on the device we will contact the Twitter API

         if (granted) {
             // Retrieve array of twitter accounts on device
             NSArray *arrayOfAccounts = [account accountsWithAccountType:accountType];
             // if there is at least one account we will contact the Twitter API
             if ([arrayOfAccounts count] > 0) {
                 ACAccount *twitterAccount = [arrayOfAccounts lastObject];
                 NSString *username = twitterAccount.username;
                 // API call that returns a user's profile
                 NSURL *requestAPI = [NSURL URLWithString:@"https://api.twitter.com/1.1/users/show.json" ];
                 // this is where we are getting the data using SLRequest
                 SLRequest *profile = [SLRequest requestForServiceType:SLServiceTypeTwitter requestMethod:SLRequestMethodGET URL:requestAPI parameters:[NSDictionary dictionaryWithObjectsAndKeys:[NSString stringWithFormat:@"%@", username], @"screen_name", @"-1", @"cursor", nil]];
                 profile.account = twitterAccount;
                 // the postRequest: method call now accesses the NSData object returned
                 [profile performRequestWithHandler:^(NSData *response, NSHTTPURLResponse *urlResponse, NSError *error) {

                     NSDictionary *profileData = [NSJSONSerialization JSONObjectWithData:response
                                                                  options:NSJSONReadingMutableContainers
                                                                    error:&error];
                     if (profileData.count > 0) {
                         NSString *profileImageURL = [profileData objectForKey:@"profile_image_url"];
                         NSURL *imageUrl = [[NSURL alloc] initWithString:profileImageURL];
                         UIImage *profileImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageUrl]];
                         _profileImageView.image = profileImage;
                         NSString *numFollowers = [profileData objectForKey:@"followers_count"];
                         _numFollowers.text = numFollowers;
                     }
                 }];
             }
         } else {
             // Handle failure to get account access
             NSLog(@"%@", [error localizedDescription]);
         }
     }];
}

Answer 1

您应该使用以下代码在前台执行更新：

dispatch_async(dispatch_get_main_queue(), ^{
    NSString *profileImageURL = [profileData objectForKey:@"profile_image_url"];
    NSURL *imageUrl = [[NSURL alloc] initWithString:profileImageURL];
    UIImage *profileImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageUrl]];
    _profileImageView.image = profileImage;
    NSString *numFollowers = [profileData objectForKey:@"followers_count"];
    _numFollowers.text = numFollowers;
});