如何使用 Flutter dart 运行计时器？

Question

I want to implement a timer in my application. Which counts from 0 and so on. If user kills the app, and open again i want to continue with the count where i killed. Can anyone help me on this. Thanks.

For example:

• User Pressed start button, Now the count starts from 00:00 .
• User kills the app at 00:20 seconds
• Again when user opens the app, the timer should starts with 00:21

Answer 1

Here's simple solution using shared_preferences and Timer .

const String _kTimeKey = 'time_s';

Future<void> main() async {
  final prefs = await SharedPreferences.getInstance();
  runApp(MyApp(dbTime: prefs.getInt(_kTimeKey)));
}

class MyApp extends StatefulWidget {
  final int dbTime;

  const MyApp({Key key, this.dbTime}) : super(key: key);

  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  SharedPreferences _prefs;
  Timer _timer;
  int _currentSeconds;

  Future<void> _saveValue() async {
    await _prefs.setInt(_kTimeKey, _currentSeconds);
    _timer?.cancel();
    _timer = null;
  }

  @override
  void initState() {
    super.initState();  
    _currentSeconds = widget.dbTime ?? 0;
    _timer = Timer.periodic(Duration(seconds: 1), (_) => setState(() => _currentSeconds++));
    SharedPreferences.getInstance().then((prefs) async {
      _prefs = prefs;
    });
  }

  @override
  Future<void> dispose() async {
    await _saveValue();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(),
        body: WillPopScope(
          onWillPop: () async {
            await _saveValue();
            return true;
          },
          child: Center(
            child: Text(
              '$_currentSeconds',
              style: TextStyle(fontSize: 50),
            ),
          ),
        ),
      ),
    );
  }
}