title: NSTimer and UIAlertController button click
body: <p>I have following simple code:</p>
  
  <pre><code>- (void)showAlert {
      countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1.0f
                                                        target:self
                                                      selector:@selector(countdown)
                                                      userInfo:nil
                                                       repeats:YES];
  
      [UIAlertController showAlertViewWithTitle:@"Title" message:@"" cancelButtonTitle:@"Dismiss" okButtonTitle:nil cancelAction:nil okAction:nil];
  }
  
  - (void)countdown {
      if(secondsLeft &gt; 0 ) {
          dispatch_async(dispatch_get_main_queue(), ^{
              _timerLabel.text = [NSString stringWithFormat:@"%ds", secondsLeft];
          });
          secondsLeft--;
      } else {
          [self showTimerLabel:NO];
          [countdownTimer invalidate];
      }
  }
  </code></pre>
  
  <p>So the timer starts together with alert display, but when I press the alert's button, there will be delay with the update for timerLabel text.</p>
  
  <p>For example, if it's on 7s, then I press button, timerLabel will jump to 5s or 4s.</p>
  
  <p>What could be wrong?</p>