使用NSURLSession下载数据并进行异步处理

Question

I am using NSURLSession to download xml files and then I want to do different processing to this files, like parsing them:

-(void)parseFeed:(NSURL *)url
{
    NSMutableURLRequest* request = [NSMutableURLRequest requestWithURL:url];

    NSURLSessionDataTask* task = [FeedSessionManager.sharedManager.session dataTaskWithRequest:request completionHandler:^(NSData* data, NSURLResponse* response, NSError* error)
                                  {
                                      Parser* parser = [[Parser alloc] initWithData:data];

                                      [self.feeds addObjectsFromArray:[parser items]];

                                  }];

    [task resume];
}

Parser object will parse the xml file using NSXMLParser . The parseFeed:(NSURL*)url is called from the ViewController :

Downloader* downloader = [[Downloader alloc] init];
[downloader parseFeed:[NSURL URLWithString:@"http://www.engadget.com/tag/features/rss.xml"]];
NSArray* items = [downloader feeds];

And this is how I create the NSURLSession object:

-(id)init
{
    if(self = [super init])
    {
        _session = [NSURLSession sessionWithConfiguration:FeedSessionConfiguration.defaultSessionConfiguration delegate:self delegateQueue:nil];
    }

    return self;
}

Of course this approach doesn't work for me. Inside parseFeed method I want to wait until all data is downloaded and processed. Only then I want to access the self.feeds array in the ViewController .

Can someone point me into the right direction into doing this ? Or maybe point me to a different approach ?

Answer 1

I have used ASIHTTPRequest but now no longer maintained but you can use AFHTTPClient's operation queue

AFHTTPClient *client = [[AFHTTPClient alloc] initWithBaseURL:nil];

// Important if only downloading one file at a time
[client.operationQueue setMaxConcurrentOperationCount: 1];

NSArray *videoURLs; // An array of strings you want to download

for (NSString * videoURL in videoURLs) {

    // …setup your requests as before

    [client enqueueHTTPRequestOperation:downloadRequest];
}