Flutter：可以使用 StreamBuilder 检测 bool 变量发生的变化吗？ 如果是，如何？ 如果没有，我可以使用什么方法？

Question

I want to manage the theme of my app. I am using SharedPreferences to store a bool value which indicate darkmode/lightmode. Whenever the user changes the mode the bool value will change. I want to change the theme of my app whenever the bool value changes. I am trying to use a streambuilder but it gives me error. I am new to flutter and I don't know whether it can be used or not. If yes, how to use it? If no, then how can I change theme while the bool value changes ? Can someone help? Here is my code

class SharedPreference {
  bool _darkmode  = false;

  get darkMode {
    return _darkmode;
  }

  setTheme(bool value) async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    preferences.setBool('isdark', value);
    _darkmode = value;
  }

  Future<bool> getTheme() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    return preferences.getBool('isdark') ?? false;
  }

}

// button to change mode

Switch.adaptive(
  value: off_on,
  activeColor: Colors.deepOrange,
  onChanged: (value) {
    setState(() => this.off_on = value);
    SharedPreference().setTheme(value);
  } 
),


// main

class _MyappState extends State<Myapp> {
  
  @override
  Widget build(BuildContext context) {
    return  StreamBuilder(
      stream: SharedPreference().darkMode,
      builder: (context, snapshot) {
        return MaterialApp(
          // theme: ThemeData(
          //   fontFamily: 'OpenSans',
          //   primarySwatch: Colors.deepOrange,
          // ),
          theme: ModeSpecifications.themeData(SharedPreference().darkMode, context),
          navigatorKey: navigatorKey,
          initialRoute: '/mainpage',
          routes: {
            '/mainpage': (context)=> MainPage(),
          },
        );
      }
    );
  }
}

I got the following errors: type 'bool' is not a subtype of type 'Stream<Object?>?'

and Unhandled Exception: MissingPluginException(No implementation found for method getAll on channel plugins.flutter.io/shared_preferences_android)

Can someone help to resolve the issue?

Answer 1

You can use a StreamController to create a stream that streamBuilder could list to. This should work.

class SharedPreference {
  final _controller = StreamController<bool>();

  Stream<bool> get darkMode async* {
    yield* _controller.stream;
  }

  void setTheme(bool value) async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    preferences.setBool('isdark', value);
    _controller.add(value); // update value here.
  }

  Future<bool> getTheme() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    return preferences.getBool('isdark') ?? false;
  }

  // call when user closes the app or something.
  void dispose() => _controller.close();
}