Flutter ChangeNotifier没有被处置

Question

我有一个更改通知程序，可以打开一个Firestore快照，并且我想关闭该应用程序以关闭快照。我尝试在dispose方法中执行关闭操作，但是在关闭应用程序时永远不会调用它。

这是主要内容：

void main() {
  runApp(MultiProvider(
    providers: [
      ChangeNotifierProvider<Auth>(create: (_) => Auth.instance()),
      ChangeNotifierProxyProvider<Auth, Api>(
        create: (_) => Api.instance(null),
        update: (_, auth, api) => Api.instance(auth.user),
      )
    ],
    child: MyApp()
  ));
}

这是ChangeNotifier：

class Api extends ChangeNotifier {
  StreamSubscription<QuerySnapshot> streamTests;
  List<Test> tests;
  FirebaseUser _user;

  set user(FirebaseUser user) {
    _user = user;

    disposeStreams();
    initStreams();
  }

  Api.instance(FirebaseUser user) {
    _user = user;
    tests = List<Test>();

    debugPrint("Api.instance");

    if (_user != null) {
      debugPrint("user != null");
      initStreams();
    }
    else {
      debugPrint("user == null");
      disposeStreams();
    }
  }

  void initStreams() {
    debugPrint("initStreams");
    streamTests = Firestore.instance
        .collection("tests")
        .where("uid", isEqualTo: _user.uid)
        .snapshots()
        .listen((querySnapshot) {
          debugPrint("querySnapshot tests " + querySnapshot.documents.length.toString());
          tests = querySnapshot.documents
            .map((d) => Test.fromMap(d.data, d.documentID))
            .toList();
          notifyListeners();
    });
  }

  void disposeStreams() {
    debugPrint("Dispose is not being called");
    if (streamTests != null) {
      streamTests.cancel();
    }
  }

  @override
  void dispose() {
    disposeStreams();
    super.dispose();
  }
}

我在做什么错？这种方法不对吗？