调用 Web 服务时对 ActivityIndi​​cator 使用 PerformSelector 的问题 - IOS

Question

我试图让 PerformSelector 在进行 Web 服务调用时在单独的线程上加载活动指示器。问题是“return parsedData;”未在 fetchJSON: 中设置。但是，当我在 getData: 方法中打印 parsedData 时，它会正常返回。我假设 return 是在 PerformSelector 完成获取数据之前执行的。有没有办法让 fetchJSON: 方法在返回 parsedData 之前等待 PerformSelector 完成？

-(void)showActivityIndicator
{ 
    CGRect frame = CGRectMake(0.0, 0.0, 125.0, 125.0);
    loading = [[UIActivityIndicatorView alloc] initWithFrame:frame];
    [loading setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleWhiteLarge];
    [loading hidesWhenStopped];
    //loading.center=[self tableView].center;
    [loading startAnimating];
    [loading sizeToFit];
    loading.autoresizingMask = (UIViewAutoresizingFlexibleLeftMargin |
                                UIViewAutoresizingFlexibleRightMargin |
                                UIViewAutoresizingFlexibleTopMargin |
                                UIViewAutoresizingFlexibleBottomMargin);

    // initing the bar button
    //UIBarButtonItem *loadingView = [[UIBarButtonItem alloc] initWithCustomView:loading];
    //loadingView.target = self;

    [loadingView addSubview:loading];
}


- (NSDictionary *)fetchJSON:(NSString *)urlString
{
    NSMutableString *domain = [[NSMutableString alloc] initWithString:@"http://www.blablabla.com/dev/"];
    [domain appendString:urlString];
    //NSLog(@"%@", domain);
    NSURL *url = [NSURL URLWithString:domain];
    NSURLRequest *req = [NSURLRequest requestWithURL:url];

    [self showActivityIndicator];
    [self performSelector:@selector(getData:) withObject:req afterDelay:0.0];
    //[self performSelectorOnMainThread:@selector(getData:) withObject:req waitUntilDone:YES];

    return parsedData;
}

-(IBAction)getData:(id)sender
{   
    NSURLResponse* response = nil;
    NSData *data = [NSURLConnection sendSynchronousRequest:sender returningResponse:&response error:nil];
    parsedData = [NSJSONSerialization
                  JSONObjectWithData:data
                  options:NSJSONReadingMutableLeaves
                  error:nil];
    NSLog(@"GET DATA %@", parsedData);
    [loading stopAnimating];
    loading = nil;
}

Answer 1

“performSelector 在单独的线程上加载活动指示器”

？？

一般来说，UIKit 不是线程安全的。

在注释掉的代码和令人困惑的方法声明之间（为什么 getData: an IBAction？它是从代码内部调用还是作为控件的操作调用？），我真的缺少有关您在这里尝试执行的操作的上下文。

您能否首先对您想要完成的任务以及该代码如何适应该情况进行高级概述？