UIActivityIndi​​catorView不会停止

Question

我正在玩iOS中的一些JSON解析,我想添加一个微调器,这很有效,但我无法阻止微调器,我想了解原因.

[spinner stopAnimating]在异步块中调用,我相信问题所在,也许是因为我不能在块中调整旋转器上的方法？我记录了微调器obj,输出是:

<UIActivityIndicatorView: 0x76905f0; frame = (150 230; 20 20); layer = <CALayer: 0x768ffb0>>

也许有人可以让我理解如何在objective-c中处理这种异步方法.我是一个绝对的初学者.

代码:

- (void)viewDidLoad{
  [super viewDidLoad];

  UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
  spinner.center = CGPointMake(160, 240);
  [self.view addSubview:spinner];
  [spinner startAnimating];


  dispatch_async(kBgQueue, ^{

    NSData* data = [NSData dataWithContentsOfURL:
                    kLatestKivaLoansURL];
    [self performSelectorOnMainThread:@selector(fetchedData:)
                           withObject:data waitUntilDone:YES];
     NSLog(@"loans: %@", spinner);
     [spinner stopAnimating];
  });


}

Answer 1

永远不要永远(永远!)与后台线程上的界面交谈.你想要的是跳回主线程 - 你正确怀疑.这很容易:

[spinner startAnimating];
dispatch_async(kBgQueue, ^{
    NSData* data = [NSData dataWithContentsOfURL:
                    kLatestKivaLoansURL];
    // ... do other stuff in the background
    dispatch_async(dispatch_get_main_queue(), ^{
        [spinner stopAnimating];
    });
});

但是,你使用performSelectorOnMainThread:withObject:waitUntilDone:with waitUntilDone:YES也是错误的(或者至少是一种非常难闻的气味),因为你不应该阻止你的后台线程.只需在后台线程上调用一个方法(除非它触及界面),当结果返回时,它会返回.