RestorationProperties

sample.packages.flutter.lib.src.widgets.restoration_properties.23.

A [StatefulWidget] that has a restorable [int] property.

  
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return WidgetsApp(
      title: 'Flutter Code Sample',
      color: const Color(0xffffffff),
      builder: (BuildContext context, Widget? child) {
        return const Center(
          child: MyStatefulWidget(restorationId: 'main'),
        );
      },
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key, this.restorationId}) : super(key: key);

  final String? restorationId;

  @override
  State createState() => _MyStatefulWidgetState();
}

/// RestorationProperty objects can be used because of RestorationMixin.
class _MyStatefulWidgetState extends State
    with RestorationMixin {
  // In this example, the restoration ID for the mixin is passed in through
  // the [StatefulWidget]'s constructor.
  @override
  String? get restorationId => widget.restorationId;

  // The current value of the answer is stored in a [RestorableProperty].
  // During state restoration it is automatically restored to its old value.
  // If no restoration data is available to restore the answer from, it is
  // initialized to the specified default value, in this case 42.
  final RestorableInt _answer = RestorableInt(42);

  @override
  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
    // All restorable properties must be registered with the mixin. After
    // registration, the answer either has its old value restored or is
    // initialized to its default value.
    registerForRestoration(_answer, 'answer');
  }

  void _incrementAnswer() {
    setState(() {
      // The current value of the property can be accessed and modified via
      // the value getter and setter.
      _answer.value += 1;
    });
  }

  @override
  void dispose() {
    // Properties must be disposed when no longer used.
    _answer.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return OutlinedButton(
      onPressed: _incrementAnswer,
      child: Text('${_answer.value}'),
    );
  }
}