NSUserDefaultsDidChangeNotification not sent

Question

While working with data sharing between iOS app and Today Extension, I faced the problem that the NSUserDefaultsDidChangeNotification is never sent from either main app or extension when I change UserDefaults. The thing is that I can read and write data to the UserDefaults successfully for the App Group I created. So the data is actually shared by the app and extension. But the notification of the UserDefaults change is never fired (or detected). Can somebody tell me what can be an issue?

The writing of the data in the UserDefaults

NSUserDefaults defaults = new NSUserDefaults("group.com.name1.name2",NSUserDefaultsType.SuiteName);
defaults.SetString("UPDATE " + DateTime.Now.Minute, "data");
defaults.Synchronize();

The notification handler

NSNotificationCenter.DefaultCenter.AddObserver(
                NSValueTransformer.UserDefaultsDidChangeNotification, (notification) => {
    NSUserDefaults defaults = new NSUserDefaults("group.com.name1.name2",NSUserDefaultsType.SuiteName);
    string str = defaults.StringForKey("data");  
});

Answer 1

So, SushiHangover provided perfectly working piece of code. However, the problem was in the Info.plist file. In order to be able to exchange the notification the Background Mode should be enable for the app with Remote Notification feature. It sounds like a very obvious thing to do, but none of the tutorials for exchanging data between Extension and app with User Defaults that I read mentioned this. Perhaps, it is an obvious thing to do. But I am writing this just in case somebody might have missed this thing too.