Flutter数据共享插件bdaya_shared_value的使用

bdaya_shared_value 是一个用于在Flutter应用中管理全局状态的插件。它基于 InheritedModel 实现，提供了一种低冗余的状态管理解决方案。以下是如何使用该插件的详细说明和示例代码。

1. 初始化

首先，需要声明一个 SharedValue 变量，并将其初始化为一个具体的值。重要的是，这个变量应声明为 final，以防止意外覆盖。

import 'package:bdaya_shared_value/bdaya_shared_value.dart';

// This global SharedValue can be shared across the entire app
// IMPORTANT: Variable declared as final
final SharedValue<int> counter = SharedValue(
  // initial value
  value: 0,
  // disk storage key for shared_preferences (optional)
  key: "counter",
  // autosave to shared prefs when value changes (optional)
  autosave: true,
);

void main() {
  runApp(
    // Don't forget this bit of initialization code!
    SharedValue.wrapApp(
      MyApp(),
    ),
  );
}

2. 使用

SharedValue 允许你在没有 BuildContext 的情况下进行读取和更新操作。这使得它在某些场景下比其他状态管理方案更为便捷。

读取和更新

void main() {
  // Read [counter]
  print(counter.$);

  // Update [counter]
  counter.$ += 1;
}

Widget build(BuildContext context) {
  // The .of(context) bit makes this widget rebuild automatically
  int counterValue = counter.of(context);

  return Text("Counter: $counterValue");
}

持久化存储

你可以通过 load() 和 store() 方法将数据保存到 shared_preferences 中：

void main() async {
  // Load [counter]'s value from shared preferences
  await counter.load();

  // Store [counter]'s value to shared preferences (enabling `autosave` does this automatically)
  await counter.store();
}

3. 完整示例

以下是一个完整的示例应用，展示了如何使用 bdaya_shared_value 进行状态管理和持久化存储。

import 'dart:async';
import 'package:bdaya_shared_value/bdaya_shared_value.dart';
import 'package:flutter/material.dart';

// This global SharedValue can be shared across the entire app
final SharedValue<int> counter = SharedValue(
  value: 0, // initial value
  key: "counter", // disk storage key for shared_preferences
  autosave: true, // autosave to shared prefs when value changes
);

final SharedValue<Duration> randomValue = SharedValue(value: Duration.zero);

void main() {
  WidgetsFlutterBinding.ensureInitialized();

  // load previous value from shared prefs
  counter.load();

  DateTime startedAt = DateTime.now();
  Timer.periodic(Duration(milliseconds: 50), (timer) {
    randomValue.$ = DateTime.now().difference(startedAt);
  });

  runApp(
    // don't forget this!
    SharedValue.wrapApp(
      MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    print("MyApp.build()");

    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: Text("Shared value demo"),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
              CounterText(),
              Padding(
                padding: const EdgeInsets.all(32),
                child: RandomText(),
              ),
            ],
          ),
        ),
        floatingActionButton: CounterButton(),
      ),
    );
  }
}

class CounterText extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    // The .of(context) bit makes this widget rebuild automatically
    int counterValue = counter.of(context);

    print("CounterText.build() - $counterValue");

    return Text(
      '$counterValue',
      style: Theme.of(context).textTheme.headline4,
    );
  }
}

class CounterButton extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    print("Button.build()");

    return FloatingActionButton(
      onPressed: _incrementCounter,
      tooltip: 'Increment',
      child: Icon(Icons.add),
    );
  }

  void _incrementCounter() {
    // update counter value and rebuild widgets
    counter.$ += 1;
  }
}

class RandomText extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Text("Your time here: ${randomValue.of(context)}");
  }
}