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February 13, 2022 08:44
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A CustomCounter example implemented with riverpod and shared_preferences using StateNotifier
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import 'package:flutter/material.dart'; | |
import 'package:flutter_riverpod/flutter_riverpod.dart'; | |
import 'package:shared_preferences/shared_preferences.dart'; | |
// A CustomCounter example implemented with riverpod and shared_preferences | |
// using StateNotifier | |
class CustomCounter { | |
final int value; | |
final DateTime dateTime; | |
const CustomCounter(this.value, this.dateTime); | |
String get counter { | |
return (value < 0) ? '-' : value.toString(); | |
} | |
String get lastUpdatedAt { | |
return dateTime.toIso8601String(); | |
} | |
String get lastUpdatedAtFormatted { | |
return "${dateTime.hour.toString().padLeft(2, '0')}:${dateTime.minute.toString().padLeft(2, '0')}:${dateTime.second.toString().padLeft(2, '0')}"; | |
} | |
} | |
class CounterStateNotifier extends StateNotifier<CustomCounter> { | |
final SharedPreferences prefs; | |
CounterStateNotifier(this.prefs) : super(CustomCounter(0, DateTime.now())) { | |
init(); | |
} | |
void init() { | |
final counter = prefs.getInt('counter'); | |
final lastUpdatedAt = prefs.getString('lastUpdatedAt'); | |
if (counter == null || lastUpdatedAt == null) { | |
state = CustomCounter(0, DateTime.now()); | |
} else { | |
state = CustomCounter(counter, DateTime.parse(lastUpdatedAt)); | |
} | |
} | |
void increment() { | |
final countPref = state.value + 1; | |
state = CustomCounter(countPref, DateTime.now()); | |
prefs.setInt('counter', state.value); | |
prefs.setString('lastUpdatedAt', state.lastUpdatedAt); | |
} | |
} | |
/// Providers are declared globally and specify how to create a state | |
final sharedPrefs = Provider<SharedPreferences>((ref) { | |
throw UnimplementedError(); | |
}); | |
final counterStateNotifier = | |
StateNotifierProvider<CounterStateNotifier, CustomCounter>( | |
(ref) => CounterStateNotifier(ref.watch(sharedPrefs))); | |
Future<void> main() async { | |
WidgetsFlutterBinding.ensureInitialized(); | |
final sharedPreferences = await SharedPreferences.getInstance(); | |
runApp( | |
// Adding ProviderScope enables Riverpod for the entire project | |
ProviderScope(overrides: [ | |
sharedPrefs.overrideWithValue(sharedPreferences), | |
], child: const MyApp()), | |
); | |
} | |
class MyApp extends StatelessWidget { | |
const MyApp({Key? key}) : super(key: key); | |
@override | |
Widget build(BuildContext context) { | |
return const MaterialApp(home: Home()); | |
} | |
} | |
class Home extends ConsumerWidget { | |
const Home({Key? key}) : super(key: key); | |
@override | |
Widget build(BuildContext context, WidgetRef ref) { | |
return Scaffold( | |
appBar: AppBar(title: const Text('Flutter101')), | |
body: Center( | |
child: Consumer(builder: (context, ref, _) { | |
final myCounter = ref.watch(counterStateNotifier); | |
return Center( | |
child: Column( | |
crossAxisAlignment: CrossAxisAlignment.center, | |
mainAxisAlignment: MainAxisAlignment.center, | |
children: [ | |
Text( | |
'Counter: ${myCounter.counter}', | |
style: DefaultTextStyle.of(context) | |
.style | |
.apply(fontSizeFactor: 3.0), | |
), | |
const SizedBox(height: 50), | |
Text( | |
myCounter.lastUpdatedAtFormatted, | |
style: DefaultTextStyle.of(context) | |
.style | |
.apply(fontSizeFactor: 3.0), | |
), | |
], | |
), | |
); | |
}), | |
), | |
floatingActionButton: FloatingActionButton( | |
onPressed: () { | |
ref.read(counterStateNotifier.notifier).increment(); | |
}, | |
child: const Icon(Icons.add), | |
), | |
); | |
} | |
} |
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