UIBarButtonItem 图像未设置

Question

我有一个很奇怪的问题。我正在 AFNetworking 的完成块内初始化一些 UI 元素，其中只有一个 (UIBarButtonItem) 未初始化。这是我的代码，位于viewDidLoad:

AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];

[m_httpClient registerHTTPOperationClass:[AFHTTPRequestOperation class]];

[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {

     NSError* error;
     self.m_pointData = [NSJSONSerialization
                        JSONObjectWithData:responseObject
                        options:kNilOptions
                        error:&error];

     [self InitializeFields];
 }
 failure:^(AFHTTPRequestOperation *operation, NSError *error)
 {
     NSLog(@"Error in get point response: %@", error);
 }];

[operation start];

}

我在 InitializeFields 中进行初始化，代码如下：

self.m_placeName.text = [self.m_pointData objectForKey:@"name"];

self.m_placeLocation.text = [self.m_pointData objectForKey:@"city"];

NSArray* comments = [self.m_pointData objectForKey:@"comments"];

const int commentsCount = [comments count];

self.m_commentsCount.text = [NSString stringWithFormat:@"%d", commentsCount];

self.m_scrollView.m_address.text = [self.m_pointData objectForKey:@"address"];
self.m_scrollView.m_email.text = [self.m_pointData objectForKey:@"email"];
self.m_scrollView.m_phone.text = [self.m_pointData objectForKey:@"tel"];
self.m_scrollView.m_link.text = [self.m_pointData objectForKey:@"website"];

self.m_rightBtn.image = [UIImage imageNamed:@"favorite_star_inactive.png"];

只有最后一行 - self.m_rightBtn.image = [UIImage imageNamed:@"favorite_star_inactive.png"]; - 不起作用。当我将其移至viewDidLoad 时，它可以工作。有完成块的东西，但我不知道是什么。

Answer 1

我可以假设这个块不在主线程中。 尝试在主线程中执行此操作：

dispatch_async(dispatch_get_main_queue(), ^{
        //update button
    });

下一个假设是，当您在块中访问图像时，图像尚未初始化。 添加检查：

if (!self.m_rightBtn.Image) {
    self.m_rightBtn.Image = [UIImage new];
}

Answer 2

UI 事情应该发生在主线程上，而不是辅助线程上（可能是完成块）。

在这个里面做 UI 的东西：

dispatch_async(dispatch_get_main_queue(), ^{
    // This block will be executed asynchronously on the main thread.
});

一切都会好起来的。有更多细节可以找到in this related question & answer。