Flutter状态机管理插件dart_state_machine的使用

Flutter状态机管理插件dart_state_machine的使用

使用

假设你的应用需要使用一个状态机来管理用户会话状态。

首先,让我们创建你的 MySessionEventMySessionState 类(实现库的 StateMachineEventStateMachineState 抽象类):

import 'package:dart_state_machine/dart_state_machine.dart';

class MySessionEvent implements StateMachineEvent {
  static const MySessionEvent login           = MySessionEvent._('login');
  static const MySessionEvent logout          = MySessionEvent._('logout');
  static const MySessionEvent logoutAndForget = MySessionEvent._('logout_and_forget');

  final String id;

  const MySessionEvent._(this.id);

  @override
  bool operator ==(Object other) =>
      identical(this, other) || 
          other is MySessionEvent && runtimeType == other.runtimeType && id == other.id;

  @override
  int get hashCode => id.hashCode;

  @override
  String toString() => '$id';
}

class MySessionState implements StateMachineState {
  static const MySessionState active    = MySessionState._('active');
  static const MySessionState inactive  = MySessionState._('inactive');
  static const MySessionState forgotten = MySessionState._('forgotten');

  final String id;

  const MySessionState._(this.id);

  @override
  bool operator ==(Object other) =>
      identical(this, other) || 
          other is MySessionState && runtimeType == other.runtimeType && id == other.id;

  @override
  int get hashCode => id.hashCode;

  @override
  String toString() => '$id';
}

然后可以使用 StateMacnineBuilder 创建一个 StateMachine

var stateMachine = StateMachineBuilder<MySessionEvent, MySessionState>()
    .setInitialState(MySessionState.active)
    .addTransition(
        Transition(
            event: MySessionEvent.login,
            statePath: [MySessionState.inactive, MySessionState.active]
        )
    )
    .addTransition(
        Transition(
            event: MySessionEvent.logout,
            statePath: [MySessionState.active, MySessionState.inactive]
        )
    )
    .addTransition(
        Transition(
            event: MySessionEvent.logoutAndForget,
            statePath: [MySessionState.active, MySessionState.forgotten]
        )
    )
    .build();

以上配置的意义在于:

  • 存在三种可能的会话状态 (active, inactiveforgotten)。
  • 存在三种可能的事件 (login, logoutlogoutAndForget)。
  • 状态机的初始状态是 active
  • 存在三种可能的状态机转换:
事件 状态路径
login inactive -> active
logout active -> inactive
logoutAndForget active -> forgotten

现在,我们可以添加监听器并操作状态机:

var listener = (MySessionState oldState, MySessionState newState) => 
    print('state change: $oldState -> $newState');

stateMachine.addListener(listener);

// 打印 "state change: active -> inactive"
var consumed = stateMachine.consumeEvent(MySessionEvent.logout);
assert(consumed);

// 无操作
consumed = stateMachine.consumeEvent(MySessionEvent.logout);
assert(!consumed);

// 打印 "state change: inactive -> active"
consumed = stateMachine.consumeEvent(MySessionEvent.login);
assert(consumed);

// 无操作
consumed = stateMachine.consumeEvent(MySessionEvent.login);
assert(!consumed);

// 打印 "state change: active -> forgotten"
consumed = stateMachine.consumeEvent(MySessionEvent.logoutAndForget);
assert(consumed);

// 无操作
consumed = stateMachine.consumeEvent(MySessionEvent.login);
assert(!consumed);

// 无操作
consumed = stateMachine.consumeEvent(MySessionEvent.logout);
assert(!consumed);

更多关于Flutter状态机管理插件dart_state_machine的使用的实战教程也可以访问 https://www.itying.com/category-92-b0.html

1 回复

更多关于Flutter状态机管理插件dart_state_machine的使用的实战系列教程也可以访问 https://www.itying.com/category-92-b0.html


当然,下面是一个关于如何在Flutter项目中使用dart_state_machine插件来管理状态机的代码示例。这个示例将展示如何定义状态、事件以及状态转换逻辑,并在Flutter UI中反映这些状态变化。

首先,确保你已经在pubspec.yaml文件中添加了dart_state_machine依赖:

dependencies:
  flutter:
    sdk: flutter
  dart_state_machine: ^x.y.z  # 请替换为最新版本号

然后,运行flutter pub get来安装依赖。

接下来,我们定义一个简单的状态机,其中包含两个状态:IdleRunning,以及两个事件:StartStop

定义状态和事件

import 'package:dart_state_machine/dart_state_machine.dart';

enum MyState { idle, running }
enum MyEvent { start, stop }

class MyStateMachine extends FiniteStateMachine<MyState, MyEvent> {
  MyStateMachine() : super(initialState: MyState.idle);

  @override
  void defineStates() {
    addState(MyState.idle, [
      Transition(MyEvent.start, MyState.running),
    ]);

    addState(MyState.running, [
      Transition(MyEvent.stop, MyState.idle),
    ]);
  }
}

在Flutter UI中使用状态机

import 'package:flutter/material.dart';
import 'package:dart_state_machine/dart_state_machine.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter State Machine Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: StateMachineDemo(),
    );
  }
}

class StateMachineDemo extends StatefulWidget {
  @override
  _StateMachineDemoState createState() => _StateMachineDemoState();
}

class _StateMachineDemoState extends State<StateMachineDemo> {
  late MyStateMachine _stateMachine;

  @override
  void initState() {
    super.initState();
    _stateMachine = MyStateMachine();
    _stateMachine.addListener(() {
      setState(() {}); // 触发UI更新
    });
  }

  void handleStartEvent() {
    _stateMachine.triggerEvent(MyEvent.start);
  }

  void handleStopEvent() {
    _stateMachine.triggerEvent(MyEvent.stop);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter State Machine Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Current State: ${describeEnum(_stateMachine.currentState)}',
              style: TextStyle(fontSize: 24),
            ),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: handleStartEvent,
              child: Text('Start'),
              style: ButtonStyle(
                backgroundColor: MaterialStateProperty.all(Colors.green),
              ),
            ),
            SizedBox(height: 10),
            ElevatedButton(
              onPressed: handleStopEvent,
              child: Text('Stop'),
              style: ButtonStyle(
                backgroundColor: MaterialStateProperty.all(Colors.red),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

解释

  1. 定义状态和事件

    • 使用enum定义了状态MyState和事件MyEvent
    • 创建了一个MyStateMachine类,继承自FiniteStateMachine<MyState, MyEvent>,并在构造函数中指定初始状态为MyState.idle
    • defineStates方法中,为每个状态定义了可能的转换。例如,从idle状态可以通过start事件转换到running状态。
  2. 在Flutter UI中使用状态机

    • 创建了一个Flutter应用,包含一个主屏幕StateMachineDemo
    • _StateMachineDemoState中,初始化了MyStateMachine实例,并添加了监听器以在状态变化时更新UI。
    • 提供了两个按钮来触发startstop事件。
    • 使用Text组件显示当前状态。

这样,当你点击“Start”按钮时,状态机会从idle转换到running,UI也会相应更新。同样,点击“Stop”按钮会将状态转换回idle

这个示例展示了如何使用dart_state_machine插件在Flutter应用中管理状态机,希望对你有所帮助!

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