Objective-C: Set timer to display a reminder using UNUserNotificationCenter

I wish to display a custom reminder or a pop up message either at the foreground or at the background of the app when it is time. I have tried this link but doesn't seems to work.

Nothing happened when I launch my app. It will say Local Notification succeeded but I don't see any pop up custom message box. Please help.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    //===Every 20 secs I will call setSchedule method
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:20 target:self selector:@selector(setSchedule) userInfo:nil repeats:YES];
    return YES;
}

-(void)setSchedule{

    NSDate *now = [NSDate date];

    NSLog(@"NSDate:%@",now);

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    [calendar setTimeZone:[NSTimeZone localTimeZone]];

    NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit|NSTimeZoneCalendarUnit fromDate:now];

    UNMutableNotificationContent *objNotificationContent = [[UNMutableNotificationContent alloc] init];

    objNotificationContent.title = [NSString localizedUserNotificationStringForKey:@"Notification!" arguments:nil];
    objNotificationContent.body = [NSString localizedUserNotificationStringForKey:@"This is local notification message!"                                                                   arguments:nil]; 
    objNotificationContent.sound = [UNNotificationSound defaultSound];

    /// 4. update application icon badge number
    objNotificationContent.badge = @([[UIApplication sharedApplication] applicationIconBadgeNumber] + 1);

    UNCalendarNotificationTrigger *trigger = [UNCalendarNotificationTrigger triggerWithDateMatchingComponents:components repeats:NO];

    UNNotificationRequest *request = [UNNotificationRequest requestWithIdentifier:@"ten"                                                                        content:objNotificationContent trigger:trigger];

    /// 3. schedule localNotification
    UNUserNotificationCenter *center = [UNUserNotificationCenter currentNotificationCenter];
    center.delegate = self;
    [center addNotificationRequest:request withCompletionHandler:^(NSError * _Nullable error) {
        if (!error) {
            NSLog(@"Local Notification succeeded");
        }
        else {
            NSLog(@"Local Notification failed");
        }
    }];

}    

First thing is that UNUserNotification not fire in foreground.

Second thing if you want to fire notification every 20 seconds or whatever time intervel then don't use UNCalendarNotificationTrigger.

Check below trigger method and set in your code.

let trigger2 = UNTimeIntervalNotificationTrigger(timeInterval: YourInterval, repeats: true)