6

我正在尝试在特定函数中实现异步 url 请求，我希望所有这些请求都完成然后执行特定操作，但该操作先于请求，即在请求完成之前调用它。

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 在 myAsyncMultipleURLRequestFunction 完成所有请求之前被调用。也尝试使用 NSOperaitonQueue 进行此操作，但无法执行我真正想要的操作。

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

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

我知道这很简单，但我的时间不多了，感谢您的帮助。

4

3 回答 3

10

@tkanzakic 走在正确的道路上。要使用的正确构造是 dispatch_group_t。但实施有待改进。通过使用信号量，您可以异步启动所有下载，并且仍然确保您没有太多的并发运行。这是一个代码示例，说明了您应该如何使用 dispatch_group_t 以​​及使所有下载并行：

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);
于 2013-04-19T13:30:59.023 回答
3

您可以创建一个dispatch_group_t然后用于dispatch_group_notify在updateUIFunction组的上一个块完成运行时执行，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];
        });
    });
});
于 2013-04-17T07:48:18.747 回答
1

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]];
    }
});

尝试这个

于 2013-04-17T08:07:49.237 回答