title: AFNetworking + download images in queue + cancel operations
body: <p>I need to download a queue of images.
  I created my operations first, then add them with the "enqueue" method of AFNetworking.</p>
  
  <p>I have 2 problems : 
  1) I didn't have the progress bar working for the queue (and I have it working with a custom operation queue)
  2) I didn't find the solution to stop the queue when I want</p>
  
  <p>I created first operations to batch and add theme in a array:</p>
  
  <pre><code>  while ((dict = [enumerator nextObject]))
    {    
      NSMutableURLRequest *request = [[MyHTTPClient sharedClient] requestWithMethod:@"GET" path:@"ws/webapp/services/pull_image" parameters:dict];
  
      AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:request
  imageProcessingBlock:nil                                                                                       cacheName:nil
      success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) 
      {
        NSLog(@"image : %@", [image description]);
        // process images
      }
      failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error)
      {
        // manage errors
      }];
  
      [operations addObject:operation];
    }
  </code></pre>
  
  <p>Then, I enqueue the operations:</p>
  
  <pre><code>     [[MyHTTPClient sharedClient] enqueueBatchOfHTTPRequestOperations:operations 
         progressBlock:^(NSUInteger numberOfCompletedOperations, NSUInteger totalNumberOfOperations) 
         {
             float percentDone = ((float)((int)numberOfCompletedOperations) / (float)((int)totalNumberOfOperations));
    [delegate syncServicesController:self updateProgressView:percentDone];
         } 
         completionBlock:^(NSArray *operations) 
        {
          //
        }];
  </code></pre>
  
  <p>So, the progress download didn't work.
  But I can see the progress of numberOfCompletedOperations... ? 1,2,3,4,5... Does I need to force the refresh of the progress view in the main thread ?</p>
  
  <p>And when I tried to stop the network tasks:</p>
  
  <pre><code>- (void)cancelAllRequests
  {
    [[MyHTTPClient sharedClient] cancelAllHTTPOperationsWithMethod:@"GET" path:@"ws/webapp/services/pull_image"];
  
  }
  </code></pre>
  
  <p>I don't understand how to stop the queue of requests... This seems that works but I have this error :  -[NSBlockOperation request]: unrecognized selector sent to instance 0x16f54c70</p>