NSURLConnection的异步不工作 [英] NSURLConnection async not working

问题描述

我试图做一个异步请求NSURL，但我发现所有的假。

I'm trying to make an asynchronous NSURL Request, but I'm getting all "FALSE."

-(BOOL)checkConnectionForHost:(NSString*)host{

   BOOL __block isOnline = NO;
   NSURLRequest *request = [[NSURLRequest alloc]initWithURL:[NSURL URLWithString:host] cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:1];
   [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
      if([(NSHTTPURLResponse*)response statusCode]==200){
         isOnline = TRUE;
      }
   }];
   NSLog(@"%i",isOnline);
   return isOnline;
}

此外，这code是被称为6时候，实际上，我只是用它了：

Also, this code is being called "6" times when I'm actually just using it with a:

-(UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath

和只有3个细胞，或在我的数据源3项。第一次处理在Objective-C异步和回调，所以详细的答复将是非常美联社preciated！谢谢！

and there are only 3 cells, or 3 items in my data source. First time dealing with async and callbacks in Objective-C, so a detailed answer would be much appreciated! Thanks!

推荐答案

您应该认识到这个问题的本身的异步的。您的与同步的方法不能的解决这个问题。也就是说，你接受的解决方案只是一个阐述和次优封装程序最终被最终异步反正。

You should realize that this problem is inherently asynchronous. You can't solve it with a synchronous approach. That is, your accepted solution is just an elaborated and suboptimal wrapper which ends up being eventually asynchronous anyway.

更好的方法是使用一个异步方法，完成处理程序，例如：

The better approach is to use an asynchronous method with a completion handler, e.g.:

typedef void (^completion_t)(BOOL isReachable);

-(void)checkConnectionForHost:(NSString*)host completion:(completion_t)completionHandler;

您可以实现如下（即使该请求是不是最佳的检查可达性）：

You can implement is as follows (even though the request isn't optimal for checking reachability):

-(void)checkConnectionForHost:(NSString*)host 
                   completion:(completion_t)completionHandler 
{
   NSURLRequest* request = [[NSURLRequest alloc]initWithURL:[NSURL URLWithString:host]];
   [NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
      if (completionHandler) {
          completionHandler(connectionError == nil && [(NSHTTPURLResponse*)response statusCode]==200);
      }
   }];
}

请注意：

• 请不要设置为短于原来的code超时。


• 完成处理程序将被要求私人线程。

用法：

[self checkConnectionForHost:self.host completion:^(BOOL isReachable){
    dispatch_async(dispatch_get_main_queue(), ^{
        self.reachableLabel.text = isReachable ? @"" : @"Service unavailable";
    });    
}];

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