Note about UNUserNotification

UNUserNotificationCenter.currentNotificationCenter.delegate = self;

UNAuthorizationOptions options = UNAuthorizationOptionAlert | UNAuthorizationOptionSound;
[UNUserNotificationCenter.currentNotificationCenter requestAuthorizationWithOptions:options
                                                                      completionHandler:^(BOOL granted, NSError * _Nullable error)
{
    if(!error){
        dispatch_async(dispatch_get_main_queue(), ^{
            [[UIApplication sharedApplication] registerForRemoteNotifications];
        });
    }
}];

// called when a notification is delivered to a foreground app.
- (void)userNotificationCenter:(UNUserNotificationCenter *)center willPresentNotification:(UNNotification *)notification withCompletionHandler:(void (^)(UNNotificationPresentationOptions options))completionHandler {
    completionHandler(UNAuthorizationOptionSound | UNAuthorizationOptionAlert);
}

// called when the user clicked the notification
- (void)userNotificationCenter:(UNUserNotificationCenter *)center didReceiveNotificationResponse:(UNNotificationResponse *)response withCompletionHandler:(void(^)(UNNotificationPresentationOptions))completionHandler {
    NSDictionary *userInfo = response.notification.request.content.userInfo;
    // customize code here
    completionHandler(UNNotificationPresentationOptionAlert);
}

// called when a remote notification is received 
// content-available should be set to true for the delegate to be called
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {
    // customize code here
    completionHandler(UIBackgroundFetchResultNoData);
}

UNMutableNotificationContent *content = UNMutableNotificationContent.new;
content.title = @"this is a title";
content.body = @"body message";
content.userInfo = @{@"userID": @(100)};
UNTimeIntervalNotificationTrigger *trigger = [UNTimeIntervalNotificationTrigger triggerWithTimeInterval:1
                                                                                                repeats:NO];
NSString *identifier = @"test";
UNNotificationRequest *request = [UNNotificationRequest requestWithIdentifier:identifier
                                                                      content:content
                                                                      trigger:trigger];
[[UNUserNotificationCenter currentNotificationCenter] addNotificationRequest:request
                                                       withCompletionHandler:^(NSError * _Nullable error)
{
    if (error) {
        // something went wrong!!
    }
}];