里面dispatch_async异步请求的url(Asynchronous url requests

我想实现特定功能异步URL请求，我希望所有这些请求完成，然后做一个具体的行动，但行动之前的要求，即，它是越来越完整的请求之前调用。

dispatch_queue_t fetchQ = dispatch_queue_create("Featured Doc Downloader", NULL);
        dispatch_async(fetchQ, ^{
            [self myAsyncMultipleURLRequestFunction];
            dispatch_sync(dispatch_get_main_queue(), ^{
                [self updateUIFunction];
            });
        });

-(void)myAsyncMultipleURLRequestFunction
   {
    for (int i=0; i<count; i++) 
     {
     NSURLConnection *loginConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];          
     }
   }

现在updateUIFunction被称为myAsyncMultipleURLRequestFunction完成所有请求之前。 也试图与NSOperaitonQueue，但不能做我真正想要的。

[_operationQ addOperationWithBlock: ^ {
     for (int i=0; i<count; i++)
      {
     NSURLConnection *loginConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];          
      }
    }

[[NSOperationQueue mainQueue] addOperationWithBlock: ^ {
         // updating UI
         [self updateUIFunction];
    }];
}];

我知道这是简单的，但我运行失控时间，任何帮助表示赞赏。

Answer 1:

@tkanzakic是在正确的道路上。 使用正确的构造是dispatch_group_t。 但执行还有待改进。 通过使用一个信号量，你可以异步启动所有下载内容，仍然确保你没有太多的同时运行。 这是说明你应该如何使用dispatch_group_t以及使你的所有下载并行代码示例：

dispatch_queue_t fetchQ = dispatch_queue_create("Featured Doc Downloader", NULL);
dispatch_group_t fetchGroup = dispatch_group_create();

// This will allow up to 8 parallel downloads.
dispatch_semaphore_t downloadSema = dispatch_semaphore_create(8);

// We start ALL our downloads in parallel throttled by the above semaphore.
for (int i=0; i<count; i++) {
    dispatch_group_async(fetchGroup, fetchQ, ^(void) {
        dispatch_semaphore_wait(downloadSema, DISPATCH_TIME_FOREVER);
        NSURLConnection *loginConnection = [[NSURLConnection alloc] initWithRequest:requestArray[i] delegate:self];
        dispatch_semaphore_signal(downloadSema);
    });
}

// Now we wait until ALL our dispatch_group_async are finished.
dispatch_group_wait(fetchGroup, DISPATCH_TIME_FOREVER);

// Update your UI
dispatch_sync(dispatch_get_main_queue(), ^{
    [self updateUIFunction];
});

// Release resources
dispatch_release(fetchGroup);
dispatch_release(downloadSema);
dispatch_release(fetchQ);

Answer 2:

您可以创建一个dispatch_group_t然后用dispatch_group_notify执行updateUIFunction当组完成运行后的前一个块，例如：

dispatch_queue_t fetchQ = dispatch_queue_create("Featured Doc Downloader", NULL);
dispatch_async(fetchQ, ^{
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        [self myAsyncMultipleURLRequestFunction];
    });
    dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
        dispatch_async(dispatch_get_main_queue(), ^{
            [self updateUIFunction];
        });
    });
});

Answer 3:

首先配置运行循环。

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSURLRequest* request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
    [NSURLConnection connectionWithRequest:request delegate:self];
    while(!self.finished) {
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
    }
});

试试这个

文章来源: Asynchronous url requests inside dispatch_async