Flutter Provider5.0状态管理使用入门

2021-03-23 本文已影响0人小源子2016

一.环境配置

environment:
  sdk: ">=2.12.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  provider: 5.0.0

二.案例

1.create: (_): 后面要接一个新创建的，而不能是已存在的变量

2.ProxyProvider被我用来把Counter的值转换为另外一个值

3.${context.watch<Translations>().title} 是监听转换后的代理值

4.() => context.read<Counter>().increment() 则是触发数据源指向动作

5.Provider状态管理类似与React的Mobox，其实我理解都是交给Provider托管的

// ignore_for_file: public_member_api_docs, lines_longer_than_80_chars
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

/// This is a reimplementation of the default Flutter application using provider + [ChangeNotifier].

void main() {
  runApp(
    /// Providers are above [MyApp] instead of inside it, so that tests
    /// can use [MyApp] while mocking the providers
    MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => Counter()),
        ProxyProvider<Counter, Translations>(
            update:(_,counter,__) => Translations(counter.count)
        )
      ],
      child: const MyApp(),
    ),
  );
}

class Translations {
  const Translations(this._value);

  final int _value;

  String get title => 'You clicked $_value times';
}

/// Mix-in [DiagnosticableTreeMixin] to have access to [debugFillProperties] for the devtool
// ignore: prefer_mixin
class Counter with ChangeNotifier, DiagnosticableTreeMixin {
  int _count = 0;

  int get count => _count;

  void increment() {
    _count++;
    notifyListeners();
  }

  /// Makes `Counter` readable inside the devtools by listing all of its properties
  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(IntProperty('count', count));
  }
}

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyHomePage(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Example'),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          mainAxisAlignment: MainAxisAlignment.center,
          children: const <Widget>[
            Text('You have pushed the button this many times:'),

            /// Extracted as a separate widget for performance optimization.
            /// As a separate widget, it will rebuild independently from [MyHomePage].
            ///
            /// This is totally optional (and rarely needed).
            /// Similarly, we could also use [Consumer] or [Selector].
            Count(),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        key: const Key('increment_floatingActionButton'),

        /// Calls `context.read` instead of `context.watch` so that it does not rebuild
        /// when [Counter] changes.
        onPressed: () => context.read<Counter>().increment(),
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Text(

      /// Calls `context.watch` to make [Count] rebuild when [Counter] changes.
        '${context.watch<Translations>().title}',
        key: const Key('counterState'),
        style: Theme.of(context).textTheme.headline4);
  }
}