Flutter 47: 图解新的状态管理 Provider (二)

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Flutter 47: 图解新的状态管理 Provider (二)

阿策~ 2019-06-03 19:46:14 浏览3422
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      小菜前几天学习了一下新的状态管理框架 ProviderProvier 支持多种类型的状态管理方式,小菜继续学习其余几种;

ListenableProvider 方式

1. 数据绑定

  1. ListenableProvider({Key key, @required ValueBuilder builder, Disposer dispose, Widget child })

      通过构造器绑定数据并进行监听,当从 Widget Tree 中删除时 dispose 要销毁;注意:构造器 builder 不可为空;

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ListenableProvider<User>(
        builder: (_) => User('Flutter', 0),
        child: MaterialApp(
            title: 'Flutter Demo',
            theme: ThemeData(primarySwatch: Colors.blue),
            home: MyHomePage(title: 'Peovider Demo')));
  }
}
  1. ListenableProvider.value({Key key, @required T listenable, Widget child })

      通过 .value 方式对数据进行监听 listenable

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ListenableProvider<User>.value(
        listenable: User('Flutter', 0),
        child: MaterialApp(
            title: 'Flutter Demo',
            theme: ThemeData(primarySwatch: Colors.blue),
            home: MyHomePage(title: 'Peovider Demo')));
  }
}

2. 获取数据

      小菜在上一篇博客中未曾提及,基本所有的获取数据方式基本相同且均支持两种方式;

  1. Provider.of(context) 方式
class ProviderText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context);
    return Text('${user.getName}');
  }
}
  1. Consumer Widget 构造器方式
class ProviderText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Consumer<User>(builder: (context, user, _) {
        return Text(user.getName);
      });
  }
}

ValueListenableProvider 方式

      使用 ValueListenableProvider 方式时要注意,需要绑定的数据要继承自 ValueNotifier,并实现其构造方法,通过对 value 的操作进行更新;小菜新建一个 person 实体类进行操作;

// 基本数据类型
class StringBean extends ValueNotifier<String> {
  StringBean(String value) : super(value);
}

// 自定义实体类
class Person extends ValueNotifier<User> {
  Person(User value) : super(value);
  String get getPersonName => value.name;

  void setPersonName(String name) {
    value.name = name;
    notifyListeners();
  }
}

1. 绑定数据

  1. ValueListenableProvider({Key key, @required ValueBuilder> builder, UpdateShouldNotify updateShouldNotify, Widget child })

      通过构造器绑定数据并进行监听,且构造器 builder 不可为空;

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ValueListenableProvider<User>(
        builder: (_) => Person(User('person', 101)),
        child: MaterialApp(
            title: 'Flutter Demo',
            theme: ThemeData(primarySwatch: Colors.blue),
            home: MyHomePage(title: 'Peovider Demo')));
  }
}
  1. ValueListenableProvider.value({Key key, @required ValueListenable valueListenable, UpdateShouldNotify updateShouldNotify, Widget child })

      通过 .value 方式对数据进行绑定监听;

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ValueListenableProvider<User>.value(
        valueListenable: Person(User('person', 101)),
        child: MaterialApp(
            title: 'Flutter Demo',
            theme: ThemeData(primarySwatch: Colors.blue),
            home: MyHomePage(title: 'Peovider Demo')));
  }
}

2. 获取数据

      获取数据的方式与上述基本一致;

class ProviderText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final number = Provider.of<String>(context);
    final person = Provider.of<User>(context);
    return Center(
        child: Column(children: <Widget>[
      Text('${number.toString()}==${person.getName}'),
      Consumer<User>(builder: (context, user, _) {
        return Text(user.getName);
      })
    ]));
  }
}

StreamProvider 方式

1. Stream 简介

      Stream 存在于 Dart:async 库中,主要用于处理异步操作;在 ListView 展示网络接口数据时曾用到过;小菜对 Stream 的理解还不够深入,基本理解为一个处理器,通过 StreamController()..sink.add() 输入需要处理的数据,通过 StreamController()..stream 输出处理后的数据;整个过程都需要通过 StreamController 来控制;具体的单 stream 和多 stream 方式小菜稍后研究;

2. 绑定数据

  1. StreamProvider({Key key, @required ValueBuilder> builder, T initialData, ..., Widget child })

      通过构建器创建 StreamController 然后绑定数据,注意需要在 initialData 中初始化绑定数据;

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamProvider<Teacher>(
        builder: (_) => StreamController<Teacher>(),
        initialData: Teacher('Teacher', 101),
        child: MaterialApp(
            title: 'Flutter Demo',
            theme: ThemeData(primarySwatch: Colors.blue),
            home: MyHomePage(title: 'Peovider Demo')));
  }
}

class Teacher {
  var tname;
  var tage;

  Teacher(this.tname, this.tage);
}

Expanded(child: TextField(
        onChanged: (changed) {
          teacher.tname = changed;
          teacher.tage = 150;
          StreamController<Teacher>().sink.add(teacher);
        },
        controller: _phonecontroller,
        decoration: InputDecoration(
            hintText: '请输入用户名',
            suffixIcon: IconButton(
                icon: Icon(Icons.clear, color: Colors.black45),
                onPressed: () {
                  _phonecontroller.clear();
                }))))
  1. StreamProvider.value({Key key, @required Stream stream, T initialData, ..., Widget child })

      通过 .value 方式对 StreamControllerstream 进行数据绑定,同样需要在 initialData 中初始化数据;

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamProvider<Teacher>.value(
        stream: StreamController<Teacher>().stream,
        initialData: Teacher('Teacher', 101),
        child: MaterialApp(
            title: 'Flutter Demo',
            theme: ThemeData(primarySwatch: Colors.blue),
            home: MyHomePage(title: 'Peovider Demo')));
  }
}

3. 获取数据

class ProviderText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final teacher = Provider.of<Teacher>(context);
    return Center(
        child: Column(children: <Widget>[
      Text('${teacher.tname}'),
      Consumer<Teacher>(builder: (context, teacher, _) {
        return Text('${teacher.tname}==${teacher.tage}');
      })
    ]));
  }
}

小结

  1. 为方便理解,结合上一节的 ChangeNotifierProvider,发现与 ListenableProviderValueListenableProvider 的使用基本相同;
class ChangeNotifierProvider<T extends ChangeNotifier>
    extends ListenableProvider<T> implements SingleChildCloneableWidget {}
class ChangeNotifier implements Listenable {}
    
class ValueListenableProvider<T>
    extends AdaptiveBuilderWidget<ValueListenable<T>, ValueNotifier<T>>
    implements SingleChildCloneableWidget {}
class ValueNotifier<T> extends ChangeNotifier implements ValueListenable<T> {}

      分析源码:ChangeNotifierProvider 继承自 ListenableProvider 且对应的 ChangeNotifier 继承自 listenable;算是 ListenableProvider 的子类;ValueNotifier 继承自 ChangeNotifier 也与 ChangeNotifierProvider 相似;

  1. 使用 ChangeNotifierProviderValueListenableProvider 绑定实体类时需要注意分别继承对应的 ChangeNotifierValueNotifier
class User with ChangeNotifier {}

class Person extends ValueNotifier<User> {}
  1. 无论使用那种 .value 方式,均建议在 dispose 中进行 listener 的关闭;
@override
void dispose() {
    stream.dispose();
    super.dispose();
}

      小菜将 Provier 中提及的五种方式均尝试了一下,对于同一类的实体类也进行测试,如有错误请多多指导!

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