如何使用GCD的NSURLRequest队列？ [英] How to make a queue of NSURLRequest using GCD?

问题描述

我有一个 NSMutableArray 包含7个互联网 URL ，从中我需要抓住 HTTP 头。

我使用这些方法来使异步所有工作完美）：

   - （void）connection：（NSURLConnection *）connection didReceiveResponse：（NSURLResponse *）response $ b $ （NSURLConnection *）连接didFailWithError：（NSError *）错误
  - （void）connectionDidFinishLoading（NSURLConnection *）连接didReceiveData：（NSData *）data 
  - ：（NSURLConnection *）connection 
  

问题是我需要下载每个 URL 遵循 NSMutableArray 的顺序，但由于异步连接的性质订单搞乱了。

我不想使用同步连接，因为它们阻塞了主线程。

如何使用 GCD > Main Thread 以确保下载将遵循我的 NSMutableArray 的索引从0到6的顺序，其中包含7 URL

感谢您的帮助！

解决方案>

你不需要GCD。您可以从第一次下载开始，并在 connectionDidFinishLoading 或 didFailWithError 中开始下一次下载。您只需要保留当前下载的索引，以便您知道是否已完成或下一步要开始下载。

以下只是一个草图这个想法：

  //开始第一个下载：
 self.currentDownload = 0; 
 request = [NSURLRequest requestWithURL：[self.myURLArray objectAtIndex：0]]; 
 connection = [NSURLConnection connectionWithRequest：request delegate：self]; 
 
 //和在connectionDidFinishLoading / didFailWithError：
 self.currentDownload ++; 
 if（self.currentDownload< self.myURLArray.count）{
 request = [NSURLRequest requestWithURL：[self.myURLArray objectAtIndex：self.currentDownload]]; 
 connection = [NSURLConnection connectionWithRequest：request delegate：self]; 
} else {
 //所有下载完成。 
} 
  

I have a NSMutableArray containing 7 internet URLs from which I need to grab the HTTP headers.

I'm using these methods to make asynchronous connections (and all works perfectly):

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
- (void)connectionDidFinishLoading:(NSURLConnection *)connection

The problem is that I need to download each URL following the order of the NSMutableArray, but due to the nature of the asynchronous connection the order gets messed up.

I don't want to use synchronous connections because they block the Main Thread.

How do I make a queue using GCD on the Main Thread to ensure that the downloads will follow the order of indexes from 0 to 6 of my NSMutableArray containing the 7 URLs?

Thanks for your help!

解决方案

You do not need GCD for that. You can start with the first download, and in connectionDidFinishLoading or didFailWithError start the next download. You would only need to maintain an index of the current download, so that you know if you are finished or which download to start next.

The following is just a sketch of this idea:

// Start the first download:
self.currentDownload = 0;
request = [NSURLRequest requestWithURL:[self.myURLArray objectAtIndex:0]];
connection = [NSURLConnection connectionWithRequest:request delegate:self];

// and in connectionDidFinishLoading/didFailWithError:
self.currentDownload++;
if (self.currentDownload < self.myURLArray.count) {
    request = [NSURLRequest requestWithURL:[self.myURLArray objectAtIndex:self.currentDownload]];
    connection = [NSURLConnection connectionWithRequest:request delegate:self];
} else {
     // All downloads finished.
}

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