title: Show next ViewController in block
body: <p>I have next simple code, for downloading info from service.</p>
  
  <pre><code>UIViewController *nextController;
  
  [request authWithBlock:^(NSDictionary *result, NSError *error) 
  {
      // Result of auth request
      if (!nextController) nextController = [UIViewController alloc] init];
      [navigationController pushViewController: nextController];
  }];
  </code></pre>
  
  <p>And I need show next view when request return success.
  I want to know - this code are correct, or I must create and show viewcontroller in another place, not in block?</p>
  
  <p>Thanks</p>