0

我有范围模型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();
}

非常简单的应用程序lib/main.dart：

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),
          );
        }
      )
    );
  }
}

我无法在小部件MainModel之外访问的问题ScopedModelDescendant。

如何MainModel在课堂开始时调用方法_MyHomePageState？

我相信这是可能的，因为我不想将所有逻辑都保留在MainModel类中并调用ScopedModelDescendant小部件中的每个方法，因为如果有很多嵌套小部件会非常不方便。

那么，如何访问范围模型StatefulWidget呢？

4

2 回答 2

1

使用作用域模型作为提供者

  • ScopedModel在使用它的小部件之前添加（MyHomePage）
  • 用于ScopedModel.of<MainModel>(context)控制模型
  • 用于ScopedModelDescendant<MainModel>聆听模型

使用这个的好处：

  • 您可以在后代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 ScopedModelDescendant 部分）

代码：

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

  @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: (context,child, model){
                return Text(
                  '${model.count}',
                  style: Theme.of(context).textTheme.headline4,
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _incrementCounter();
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

将 MainModel 作为单例

作为您的解决方案，您创建一次 MainModel 并使其成为最终模型。这可以更简单，如下所示：

主模型

final MainModel mainModel = MainModel();

class MainModel{
  int _count = 0;

  int get count {
    return _count;
  }

  void incrementCount() {
    _count += 1;
  }

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

我的主页

  • MainModel甚至不需要扩展模型或使用 notifyListeners 因为小部件用于setState重建

代码：

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();
    });
  }

  @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:',
            ),
            Text(
              '${mainModel.count}',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _incrementCounter();
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}
于 2021-01-14T16:26:04.210 回答
0

在观察了我的代码一段时间后，我意识到修复它是多么愚蠢。

因此，显然项目的所有小部件和文件都应该只有一个实例，MainModel()并且为了方便起见，它应该lib/scoped_models/main.dart像这样放置在作用域模型文件中：

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();
}

然后您可以mainModel在导入模型的任何地方使用实例import 'package:<app_name>/scoped_models/main.dart';

因此，此代码将有效lib/main.dart：

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),
          );
        }
      )
    );
  }
}

尽管这似乎是合理的事实，但由于缺乏示例，它也可能是第一次压倒性的。

于 2021-01-14T09:22:14.407 回答