EXC_BAD_ACCESS

AppViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];
    [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:@selector(onTimer) userInfo:nil repeats:YES];
    
    if (![[NSUserDefaults standardUserDefaults] objectForKey:kCurrentPage]) {
        [[NSUserDefaults standardUserDefaults] setInteger:1 forKey:kCurrentPage];
        currentPage = 1;
    } else {
        currentPage = [[NSUserDefaults standardUserDefaults] integerForKey:kCurrentPage];
    }
}

- (void)onTimer {
    NSLog(@"Current page is %@", currentPage);
}