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 TestWidget
Widget _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A
class ATestWidget extends TestWidget<A> {
 const ATestWidget({Key? key}) : super(key: key);
 @override
 Widget childBuilder(A param) {
 return AWidget(a: param);
 }
}
/// 实例B
class BTestWidget extends TestWidget<B> {
 const BTestWidget({Key? key}) : super(key: key);
 @override
 Widget childBuilder(B param) {
 return BWidget(b: param);
 }
}
作者:李小轰_Rex

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