Flutter 颤振：StatefulWidget中的作用域模型访问

我有作用域模型

lib/scoped_models/main.dart

：

import 'package:scoped_model/scoped_model.dart';

class MainModel extends Model {
  int _count = 0;

  int get count {
    return _count;
  }
  
  void incrementCount() {
    _count += 1;
    notifyListeners();
  }

  void setCount(int value) {
    _count = value;
    notifyListeners();
}

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import 'package:scoped_m_test/scoped_models/main.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ScopedModel<MainModel>(
        model: MainModel(),
        child: MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
            visualDensity: VisualDensity.adaptivePlatformDensity,
          ),
          home: MyHomePage(title: 'Flutter Demo Home Page'),
        )
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final MainModel _model = MainModel();

  void initState() {
    super.initState();
    // _model.incrementCount(); // <-- doesn't work !!!
  }
  
  void _incrementCounter() {
    setState(() {
      // _model.incrementCount(); // <-- doesn't work !!!
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            ScopedModelDescendant<MainModel>(
              builder: (BuildContext context, Widget child, MainModel model) {
                return Text(
                  '${model.count}',
                  style: Theme.of(context).textTheme.headline4,
                );
              }
            )
          ],
        ),
      ),
      floatingActionButton: ScopedModelDescendant<MainModel>(
        builder: (BuildContext context, Widget child, MainModel model) {
          return FloatingActionButton(
            onPressed: () {
              model.incrementCount(); // <-- only this works !!!
              // _incrementCounter(); // <-- doesn't work !!!
            },
            tooltip: 'Increment',
            child: Icon(Icons.add),
          );
        }
      )
    );
  }
}

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import 'package:scoped_m_test/scoped_models/main.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ScopedModel<MainModel>(
        model: mainModel, // <-- instance of model from 'lib/<app_name>/scoped_models/main.dart'
        child: MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
            visualDensity: VisualDensity.adaptivePlatformDensity,
          ),
          home: MyHomePage(title: 'Flutter Demo Home Page'),
        )
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  void initState() {
    super.initState();
  }
  
  void _incrementCounter() {
    setState(() {
      mainModel.incrementCount(); // <-- now it works !!!
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            ScopedModelDescendant<MainModel>(
              builder: (BuildContext context, Widget child, MainModel model) {
                return Text(
                  '${model.count}',
                  style: Theme.of(context).textTheme.headline4,
                );
              }
            )
          ],
        ),
      ),
      floatingActionButton: ScopedModelDescendant<MainModel>(
        builder: (BuildContext context, Widget child, MainModel model) {
          return FloatingActionButton(
            onPressed: () {
              // model.incrementCount(); // <-- works !!!
              _incrementCounter(); // <-- now it's working too !!!
            },
            tooltip: 'Increment',
            child: Icon(Icons.add),
          );
        }
      )
    );
  }
}

非常简单的应用程序

lib/main.dart

：

import 'package:scoped_model/scoped_model.dart';

class MainModel extends Model {
  int _count = 0;

  int get count {
    return _count;
  }
  
  void incrementCount() {
    _count += 1;
    notifyListeners();
  }

  void setCount(int value) {
    _count = value;
    notifyListeners();
}

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import 'package:scoped_m_test/scoped_models/main.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ScopedModel<MainModel>(
        model: MainModel(),
        child: MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
            visualDensity: VisualDensity.adaptivePlatformDensity,
          ),
          home: MyHomePage(title: 'Flutter Demo Home Page'),
        )
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final MainModel _model = MainModel();

  void initState() {
    super.initState();
    // _model.incrementCount(); // <-- doesn't work !!!
  }
  
  void _incrementCounter() {
    setState(() {
      // _model.incrementCount(); // <-- doesn't work !!!
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            ScopedModelDescendant<MainModel>(
              builder: (BuildContext context, Widget child, MainModel model) {
                return Text(
                  '${model.count}',
                  style: Theme.of(context).textTheme.headline4,
                );
              }
            )
          ],
        ),
      ),
      floatingActionButton: ScopedModelDescendant<MainModel>(
        builder: (BuildContext context, Widget child, MainModel model) {
          return FloatingActionButton(
            onPressed: () {
              model.incrementCount(); // <-- only this works !!!
              // _incrementCounter(); // <-- doesn't work !!!
            },
            tooltip: 'Increment',
            child: Icon(Icons.add),
          );
        }
      )
    );
  }
}

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import 'package:scoped_m_test/scoped_models/main.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ScopedModel<MainModel>(
        model: mainModel, // <-- instance of model from 'lib/<app_name>/scoped_models/main.dart'
        child: MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
            visualDensity: VisualDensity.adaptivePlatformDensity,
          ),
          home: MyHomePage(title: 'Flutter Demo Home Page'),
        )
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  void initState() {
    super.initState();
  }
  
  void _incrementCounter() {
    setState(() {
      mainModel.incrementCount(); // <-- now it works !!!
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            ScopedModelDescendant<MainModel>(
              builder: (BuildContext context, Widget child, MainModel model) {
                return Text(
                  '${model.count}',
                  style: Theme.of(context).textTheme.headline4,
                );
              }
            )
          ],
        ),
      ),
      floatingActionButton: ScopedModelDescendant<MainModel>(
        builder: (BuildContext context, Widget child, MainModel model) {
          return FloatingActionButton(
            onPressed: () {
              // model.incrementCount(); // <-- works !!!
              _incrementCounter(); // <-- now it's working too !!!
            },
            tooltip: 'Increment',
            child: Icon(Icons.add),
          );
        }
      )
    );
  }
}

导入“包装：颤振/材料.省道”；
导入“package:scoped_model/scoped_model.dart”；
导入“package:scoped_m_test/scoped_models/main.dart”；
void main（）{
runApp（MyApp（））；
}
类MyApp扩展了无状态小部件{
@凌驾
小部件构建（构建上下文）{
返回范围模型(
模型：MainModel（），
孩子：MaterialApp(
标题：“颤振演示”，
主题：主题数据(
主样本：颜色。蓝色，
视觉密度：视觉密度。自适应平台密度，
),
主页：MyHomePage（标题：“颤振演示主页”），
)
);
}
}
类MyHomePage扩展StatefulWidget{
MyHomePage（{Key，this.title}）：超级（Key:Key）；
最后的字符串标题；
@凌驾
_MyHomePageState createState（）=>\u MyHomePageState（）；
}
类_MyHomePageState扩展状态{
最终主模型_model=MainModel（）；
void initState（）{
super.initState（）；
//_model.incrementCount（）；//在查看了我的代码一段时间后，我意识到修复代码是多么简单

因此，显然，对于项目的所有小部件和文件，应该只有一个
MainModel（）
实例，为了方便起见，应该将其放置在作用域模型文件
lib/scoped_models/main.dart
中，如下所示：

import 'package:scoped_model/scoped_model.dart';

final MainModel mainModel = MainModel(); // <-- create instance once for all files which require scoped model import

class MainModel extends Model {
  int _count = 0;

  int get count {
    return _count;
  }
  
  void incrementCount() {
    _count += 1;
    notifyListeners();
  }

  void setCount(int value) {
    _count = value;
    notifyListeners();
}

尽管这一事实似乎是合理的，但由于缺乏示例，它也可能第一次被淹没。我希望这对某些人有所帮助。
使用作用域模型作为提供者

在使用它的小部件（MyHomePage）之前添加
ScopedModel
使用
ScopedModel.of（context）
控制模型
使用
scopedModeleScendant
收听模型

使用此选项的优点是：


您可以在子体中访问相同的模型并轻松共享数据
尽可能小地重建小部件（仅重建ScopedModelSecondant部分）

代码：

MyHomePage


MainModel
甚至不需要扩展模型或使用notifyListeners，因为小部件使用
setState
来重建

代码：

类MyHomePage扩展StatefulWidget{
MyHomePage（{Key，this.title}）：超级（Key:Key）；
最后的字符串标题；
@凌驾
_MyHomePageState createState（）=>\u MyHomePageState（）；
}
类_MyHomePageState扩展状态{
void initState（）{
super.initState（）；
}
void _incrementCounter（）{
设置状态（）{
mainModel.incrementCount（）；
});
}
@凌驾
小部件构建（构建上下文）{
返回脚手架(
appBar:appBar(
标题：文本（widget.title），
),
正文：中(
子：列(
mainAxisAlignment:mainAxisAlignment.center，
儿童：[
正文(
“您已经按了这么多次按钮：”，
),
正文(
“${mainModel.count}”，
风格：Theme.of（context）.textTheme.headline4，
),
],
),
),
浮动操作按钮：浮动操作按钮(
已按下：（）{
_递增计数器（）；
},
工具提示：“增量”，
子：图标（Icons.add），
),
);
}
}
你把你的
mainModel
作为一个全局单体，这有点奇怪，为什么你还需要
ScopedModel
呢？你可以简单地使用
class mainModel extends change notifier
并在任何地方读/写它。谢谢你的评论，但我不知道如何正确地实现你的方法。我试着在另一方面解释它回答。如果你有任何进一步的问题，请告诉我。