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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，它会恢复正常。我假设在 performSelector 完成获取数据之前执行返回。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;
}
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1 回答 1

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“执行选择器在单独的线程上加载活动指示器”

??

UIKit 通常不是线程安全的。

在注释掉的代码和令人困惑的方法声明之间（为什么是 getData: 一个 IBAction？它是从代码内调用还是作为控件的操作调用？），我真的错过了你在这里尝试做的事情的上下文。

您是否可以先简要概述一下您要完成的工作以及此代码如何适合该图片？

于 2012-02-02T01:17:45.140 回答