Flutter: how to run a code when user closes app?

Question

I have the following subscription:

class CheckInternet with ChangeNotifier {
  StreamSubscription<ConnectivityResult> _subscription;
  bool haveInternet = false;

  static CheckInternet _instance;

  static CheckInternet getInstance() {
    if (_instance == null) {
      _instance = CheckInternet();
      _instance.checkConnectivity();
    }

    return _instance;
  }

  void checkConnectivity() {
    if (_subscription == null) {
      _subscription = Connectivity()
          .onConnectivityChanged
          .listen((ConnectivityResult result) {
        bool res = result == ConnectivityResult.mobile ||
            result == ConnectivityResult.wifi;
        setHaveInternet = res;
      });
    }
  }

I create this subscription in my main() method and while the app is open, it is checking the internet connection. My problem is that how to make a method what will cancel the subscription when the user closes the app.

I need something like the dispose() is for widgets.