Detect alert view

//
//  ViewController.m
//  DetectAlertView
//
//  Created by Dominique d'Argent on 4/14/13.
//  Copyright (c) 2013 Dominique d'Argent. All rights reserved.
//

#import "ViewController.h"

@implementation ViewController

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    
    UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    [self.view addSubview:spinner];
    
    
    [spinner startAnimating];
    
    // Show alert view in 2 seconds
    double delayInSeconds = 2.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        [[[UIAlertView alloc] initWithTitle:@"Alert"
                                   message:@"Message"
                                  delegate:nil
                         cancelButtonTitle:@"Cancel"
                         otherButtonTitles:@"OK", nil] show];
    });
    
    [[NSNotificationCenter defaultCenter] addObserverForName:UIWindowDidBecomeKeyNotification
                                                      object:nil
                                                       queue:[NSOperationQueue mainQueue]
                                                  usingBlock:^(NSNotification *note) {
                                                      UIWindow *window = [note object];
                                                      
                                                      for (UIView *view in window.subviews) {
                                                          if ([view isKindOfClass:[UIAlertView class]]) {
                                                              NSLog(@"ALERT!!!");
                                                              [spinner stopAnimating];
                                                          }
                                                      }
                                                  }];
}

@end

Although this looks very promising, it does not work in my scenario (both the dispatch_async and UINotification approach). This is probably because of how the alert is displayed in my case (it's a system alert). There is no UIAlertView in the view hirarchy of any window. This works for me:

__block id alertObserver;
alertObserver = [[NSNotificationCenter defaultCenter]
    addObserverForName:UIApplicationWillResignActiveNotification
    object:nil
    queue:[NSOperationQueue mainQueue]
    usingBlock:^(NSNotification *note) {
        [spinner stopAnimating];
        [[NSNotificationCenter defaultCenter] removeObserver:alertObserver];
    }
];