Dart多态控制反转编码规范实例详解
前言
我们通常都知道程序设计要依赖抽象，提高复用性，做到对扩展开放，对修改关闭。贯彻SOLID五大原则的最重要法宝就是抽象和继承。多态是一种手段，下面，通过简单 demo 介绍 flutter 开发中常用的最佳实践。
举栗子🌰
/// 不推荐，避免把逻辑放在公共底层处理class TestWidget extends StatefulWidget { const TestWidget({Key? key}) : super(key: key); @override TestWidgetState createState() => TestWidgetState();}class TestWidgetState extends State<TestWidget> { dynamic param; Widget childWidget = Container(); ///提供给外部调用 void update(dynamic value) { setState(() { param = value; _updateBody(); }); } void _updateBody(){ if(param == null){ childWidget = Container(); return; } switch(param.runtimeType){ case A: childWidget = AWidget(a: param as A,); break; case B: childWidget = BWidget(b: param as B,); break; default: childWidget = Container(); break; } } @override Widget build(BuildContext context) { return Container( child: childWidget, ); }}如上的写法是不推荐的，应该进行依赖倒置，将可变的部分放上层处理，保证底层干净，如下：
方式一：通过传参构造器进行控制反转
typedef ChildBuilder = Widget Function(dynamic param);class TestWidget extends StatefulWidget { final ChildBuilder builder; const TestWidget({Key? key, required this.builder}) : super(key: key); @override TestWidgetState createState() => TestWidgetState();}class TestWidgetState extends State<TestWidget> { dynamic param; void update(dynamic value) { setState(() { param = value; }); } @override Widget build(BuildContext context) { return Container( child: widget.builder(param), ); }}///外部使用 TestWidgetWidget _builder(dynamic param){ if (param == null) { return Container(); } switch (param.runtimeType) { case A: return AWidget( a: param as A, ); case B: return BWidget( b: param as B, ); default: return Container(); }}return TestWidget(builder: _builder);方式二：通过继承 + 泛型进行解耦
/// 将 TestWidget 改成抽象类并指定泛型abstract class TestWidget<T> extends StatefulWidget { const TestWidget({Key? key}) : super(key: key); Widget childBuilder(T param); @override TestWidgetState<T> createState() => TestWidgetState<T>();}class TestWidgetState<T> extends State<TestWidget> { T? param; Widget childWidget = Container(); void update(T value) { setState(() { param = value; }); } @override Widget build(BuildContext context) { return Container( child: widget.childBuilder(param), ); }}/// 实例Aclass ATestWidget extends TestWidget<A> { const ATestWidget({Key? key}) : super(key: key); @override Widget childBuilder(A param) { return AWidget(a: param); }}/// 实例Bclass BTestWidget extends TestWidget<B> { const BTestWidget({Key? key}) : super(key: key); @override Widget childBuilder(B param) { return BWidget(b: param); }}以上就是Dart 多态 控制反转的详细内容
