网站集约化建设存在的困难网上售卖平台有哪些

Flutter 如果界面上有数据更新时，目前学习到的有3种：

• 第一种： 直接用 StatefulWidget组件，然后当数据更新时，调用setState的方法更新数据，页面上的数据会直接更新；
• 第二种： 用 StatefulWidget组件 和 InheritedWidget 的结合，这种模式比较适用于有比较多层级的场景；这样数据更新时，就不用一层一层的从父类上传递数据；
• 第三种：用第三方库scoped_model, 这种模式下在StatelessWidget也可以实现UI页面上数据的更新。

如要实现下面这个页面的效果（点击 count:x 和底部"+", 实现count的数据加1）：

1. StatefulWidget 更新数据的使用

这个比较简单，代码如下：

import 'package:flutter/material.dart';class StatemanagerDemo extends StatefulWidget {const StatemanagerDemo({super.key});@overrideState<StatemanagerDemo> createState() => _StatemanagerDemoState();
}class _StatemanagerDemoState extends State<StatemanagerDemo> {int _count = 0;void _increaseCount() {// 这个是关键，只有调用 setState 才能更新页面的数据setState(() {_count += 1;});}@overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text("StateManagerDemo"),),body: CounterWidget(count: _count, increaseCount: _increaseCount),floatingActionButton:  FloatingActionButton(onPressed: _increaseCount,child: Icon(Icons.add),),);}
}class CounterWidget extends StatelessWidget {final int count;final VoidCallback increaseCount;const CounterWidget({super.key, required this.count, required this.increaseCount});@overrideWidget build(BuildContext context) {return Center(child: ActionChip(label: Text("$count"),onPressed: increaseCount));}
}

2. StatefulWidget组件 和 InheritedWidget 的结合

代码如下：

//-------用InheritedWidget 实现数据的更新------
class StateManagerInheriteDemo extends StatefulWidget {const StateManagerInheriteDemo({super.key});@overrideState<StateManagerInheriteDemo> createState() => _StateManagerInheriteDemoState();
}class _StateManagerInheriteDemoState extends State<StateManagerInheriteDemo> {int _count = 0;void _increaseCount() {setState(() {_count += 1;});}@overrideWidget build(BuildContext context) {return CounterProvider(count: _count, increaseCount: _increaseCount, child: Scaffold(appBar: AppBar(title: Text("StateManagerDemo"),),body: CounterWidgetInherite(),floatingActionButton:  FloatingActionButton(onPressed: _increaseCount,child: Icon(Icons.add),),));}
}// 创建一个provider类来提供全局可用的数据存储和获取
class CounterProvider extends InheritedWidget {final int count;final VoidCallback increaseCount;final Widget child;const CounterProvider({super.key, required this.count, required this.increaseCount, required this.child}) : super(child: child);// 定义一个of方法，可以获取CounterProvider的数据static CounterProvider? of(BuildContext context) => context.dependOnInheritedWidgetOfExactType<CounterProvider>();@overridebool updateShouldNotify(covariant InheritedWidget oldWidget) {return true;}
}// 模拟多个层级1
class CounterWidgetInherite extends StatelessWidget {const CounterWidgetInherite ({super.key});@overrideWidget build(BuildContext context) {return Center(child: Counter(),);}
}// 模拟多个层级2
class Counter extends StatelessWidget {const Counter({super.key});@overrideWidget build(BuildContext context) {final int? count = CounterProvider.of(context)?.count;final VoidCallback? increaseCount = CounterProvider.of(context)?.increaseCount;return ActionChip(label: Text("$count"),onPressed: increaseCount,);}
}

3. scoped_model 的使用

scoped_model 是第三方库，需要在项目中引入三方库（引入三方库的方法，参考这个文章）；其次，该模式引用到的组件主要是：

• ScopedModel
• ScopedModelDescendant

原理还没搞明白，只是看着视频实现了功能，代码如下：

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';//-------用Scoped_Model 实现数据的更新-----
class StateManagerScopteModelDemo extends StatelessWidget {const StateManagerScopteModelDemo({super.key});@overrideWidget build(BuildContext context) {// 用ScopedModel 包装一下，提供model属性对应的类型return ScopedModel(model: CounterModel(), child: Scaffold(appBar: AppBar(title: Text("StateManagerDemo"),),body: CounterWidgetScopteModel(),// ScopedModelDescendant 的构建方法获取CounterModel对应的数据floatingActionButton:  ScopedModelDescendant<CounterModel>(rebuildOnChange: false,builder: (context, _, model) {return FloatingActionButton(onPressed: model.increaseCount,child: Icon(Icons.add),);}),));}
}class CounterWidgetScopteModel extends StatelessWidget {const CounterWidgetScopteModel ({super.key});@overrideWidget build(BuildContext context) {return Center(// ScopedModelDescendant 的构建方法获取CounterModel对应的数据child: ScopedModelDescendant<CounterModel>(builder: (context, _, model) {return ActionChip(label: Text("count: ${model.count}"),onPressed: model.increaseCount,);}),);}
}// 创建继承于Model的业务类，来存放对应的count和用到的方法
class CounterModel extends Model {int _count = 0;int get count => _count;void increaseCount() {_count += 1;// 使用Model小部件的地方会监听Model的变化，可以用notifyListeners方法重建UI notifyListeners();}
}