Objective-C – ASINetworkQueue执行添加的请求两次？

Question

我正在使用 ASINetworkQueue 对我的请求进行排队。而我添加了 12 个请求，最终它下载了 24 次，每个请求下载两次？这是为什么？我该如何预防呢？

在调用队列上的 go 之前，我检查已添加到队列中的请求数 (NSLog(@"%@",[[self queue] actions]);) 并显示 12 个 ASIHTTPRequest。

编辑：添加了我的代码。我没有打开准确进度。

代码：

- (void)setupQueue {

    DLog(@"setupQueue running");

    // Stop anything already in the queue before removing it
    [[self queue] cancelAllOperations];

    // Creating a new queue each time we use it means we don't have to worry about clearing delegates or resetting progress tracking
    [self setQueue:[ASINetworkQueue queue]];
    [[self queue] setDelegate:self];

    [[self queue] setRequestDidStartSelector:@selector(requestStarted:)];
    [[self queue] setRequestDidFinishSelector:@selector(requestFinished:)];
    [[self queue] setRequestDidFailSelector:@selector(requestFailed:)];
    [[self queue] setQueueDidFinishSelector:@selector(queueFinished:)];

}

- (NSArray *)parseMapsThumbsUrls {

    DLog(@"parseMapsThumbsUrls running");

    NSDictionary *results = [[self officesJSON] JSONValue];

    NSArray *offices = [results objectForKey:@"offices"];

    NSMutableArray *mapsThumbsUrls = [[[NSMutableArray alloc] init] autorelease];

    for (NSDictionary *office in offices) {

        NSString *mapThumbImageString = [NSString stringWithFormat:@"http://maps.google.com/maps/api/staticmap?zoom=11&markers=color:0xFF7300|%@,%@&size=70x70&sensor=true", [office objectForKey:@"latitude"], [office objectForKey:@"longitude"]];

        // Make the string HTML-compatible
        NSString *url = [mapThumbImageString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

        [mapsThumbsUrls addObject:url];

    }

    return mapsThumbsUrls; // returns an array of 6 urls
}

- (void)downloadMapsThumbs {

    DLog(@"downloadMapsThumbs running");

    [self setupQueue]; 

    NSArray *mapsThumbsUrls = [self parseMapsThumbsUrls];

    for (NSString *mapThumbUrl in mapsThumbsUrls) {

        NSURL *url = [NSURL URLWithString:mapThumbUrl];
        ASIHTTPRequest *mapThumbRequest = [ASIHTTPRequest requestWithURL:url];

        [mapThumbRequest setTag:2];

        [mapThumbRequest setDelegate:self];

        [[self queue] addOperation:mapThumbRequest];
    }
}

- (void)download {

    [self downloadMapsThumbs];

    DLog(@"%@",[[self queue] operations]);
    [[self queue] go];
}

- (void)requestFinished:(ASIHTTPRequest *)request {


    if (request.tag == 2) { // Process thumbs

        DLog(@"%@",[[request originalURL] description]);

        // Use when fetching binary data
        NSData *responseData = [request responseData];
        [[self mapThumbs] addObject:responseData];

    }

}

Answer 1

我注意到我正在为队列和单个请求设置委托，这就是请求下载两次的原因。

Answer 2

引用文档：

当您启动一个启用了精确进度的队列时，它会首先对队列中的所有 GET 请求执行 HEAD 请求，以获取要下载的数据的总大小。一旦掌握了总大小，就可以准确显示总进度，真正的请求就会开始。

这将导致队列中的每个条目都有两个 HTTP 请求，因此它也许可以解释您所看到的内容？