NSURLSessionDataTask不能在子线程中工作

Question

作为标题 NSData *data = [NSData dataWithContentsOfURL:URL];现在我想用NSURLSessionDataTask替换它。但是我有一个问题，就是NSURLSessionDataTask没有成功返回数据 我试图打破断点并发现它在主线程中运行，但它没有运行。

//1 on main thread
NSURLSessionDataTask *loadDataTask = [session dataTaskWithURL:URL completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    // don't work
    dataU = data;

    TFHpple *hpple = [[TFHpple alloc] initWithHTMLData:dataU];initWithHTMLData:dataU];

    NSString *pathQueryString = @"//div[@class='newslist l']/ul/li/a"; //
    NSArray *Nodes = [hpple searchWithXPathQuery:pathQueryString];

    for (TFHppleElement *element in Nodes) {

        MKNewsItem *newsItem = [[MKNewsItem alloc] init];

        // 6
        newsItem.title = [element text];
        newsItem.time = [[element firstChildWithTagName:@"span"] content];
        NSMutableString *tempTime = [NSMutableString stringWithFormat:@"%@", newsItem.time];
        [tempTime replaceCharactersInRange:NSMakeRange(0, 1) withString:@""];
        [tempTime replaceCharactersInRange:NSMakeRange(10, 1) withString:@""];
        newsItem.time = tempTime;

        newsItem.url = [NSURL URLWithString:[element objectForKey:@"href"]];

        NSMutableString *tempUrl = [NSMutableString stringWithFormat:@"http://www.ayit.edu.cn%@",newsItem.url.absoluteString];
        [tempUrl deleteCharactersInRange:NSMakeRange(22, 2)];  //删除那两个..
        newsItem.url = [NSURL URLWithString:tempUrl];
        [newsGroup addObject:newsItem];
    }
    _news = nil;
    _news = newsGroup;

}];

//2  
[loadDataTask resume];

实施NSURLSessionDataTask

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