NSURLSession for HTTP data task(NSURLSessionDataTask)是否在后台线程中运行,或者我们必须提供队列？

Question

我现在开始使用NSURLSession,NSURLConnection因为它是Apple提供的一种新的优雅API.以前,我曾经NSURLRequest在GCD块中调用来在后台执行它.以下是我过去的做法:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    NSURLRequest *request = [NSURLRequest requestWithURL:
                             [NSURL URLWithString:@"www.stackoverflow.com"]];
    NSURLResponse *response;
    NSError *error;
    NSData *data = [NSURLConnection sendSynchronousRequest:request 
                                         returningResponse:&response 
                                                     error:&error];
    if (error) {
        // handle error
        return;
    }
    dispatch_async(dispatch_get_main_queue(), ^{
        // do something with the data
    });
});

现在,我的使用方法NSURLSession如下:

- (void)viewDidLoad 
{
    [super viewDidLoad];

    /*-----------------*
        NSURLSession
     *-----------------*/

    NSURLSession *session = [NSURLSession sharedSession];

    NSURLSessionDataTask *dataTask = [session dataTaskWithURL:
                                  [NSURL URLWithString:@"https://itunes.apple.com/search?term=apple&media=software"] 
                                     completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) 
{
    NSDictionary *json = [NSJSONSerialization 
                          JSONObjectWithData:data options:0 error:nil];
    NSLog(@"%@", json);
}];
}

我想知道,我的请求是否会在后台线程本身执行,或者我必须以同样的方式提供我自己的机制NSURLRequest？

Answer 1

不,您不需要使用GCD将其分配给后台队列.事实上,因为完成块在后台线程上运行,所以完全相反,如果你需要在该块中运行任何东西(例如,模型对象的同步更新,UI更新等),那么手动将其自行调度到主队列.例如,让我们假设您要检索结果列表并更新UI以反映这一点,您可能会看到如下内容:

- (void)viewDidLoad 
{
    [super viewDidLoad];

    NSURLSession *session = [NSURLSession sharedSession];

    NSURLSessionDataTask *dataTask = [session dataTaskWithURL:[NSURL URLWithString:@"https://itunes.apple.com/search?term=apple&media=software"] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        // this runs on background thread

        NSError *error;
        NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];

        // detect and handle errors here

        // otherwise proceed with updating model and UI

        dispatch_async(dispatch_get_main_queue(), ^{
            self.searchResults = json[@"results"];    // update model objects on main thread
            [self.tableView reloadData];              // also update UI on main thread
        });

        NSLog(@"%@", json);
    }];

    [dataTask resume];
}