NSURLConnection异步无法正常工作

Question

我正在尝试创建一个异步NSURL请求,但我得到了所有"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,当我实际上只使用它时,此代码被称为"6"次:

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

并且我的数据源中只有3个单元格或3个项目.第一次在Objective-C中处理异步和回调,所以非常感谢详细的答案!谢谢!

Answer 1

异步调用将并行执行,其结果将在完成块中接收.在您的情况下,将在完成异步请求之前执行return语句.这将永远是错误的.

您应该为此使用同步请求,并处理不阻止UI.

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

    BOOL isOnline = NO;
    NSURLRequest *request = [[NSURLRequest alloc]initWithURL:[NSURL URLWithString:host] cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:1];
    NSHTTPURLResponse *response;
    NSError *error;

    NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

    NSLog(@"Response status Code : %d",response.statusCode);
    isOnline = response.statusCode == 200;

    return isOnline;    
}

您可以在调度队列中使用该方法,

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul);
dispatch_async(queue, ^{
    BOOL status = [self checkConnectionForHost:@"http://google.com"];
    NSLog(@"Host status : %@",status ? @"Online" : @"Offline");
});