这个问题的关键在于如何处理状态变化，最好由原始祖先自动处理。 在我看来，不可能继续扩展这些类 将StatefulWidget作为祖先的第一个孩子（例1）？
在我看来，使用mixins是唯一的方法。 但是这有一个缺点，你必须手动管理状态更改（例2）。
我忽略了什么吗？
//示例1 - 不能用作BarState剂量不从Bar继承
class Foo extends StatefulWidget {
final String stringFoo;
Foo({Key key, this.stringFoo}) : super(key: key);
@override
FooState createState() => new FooState();
}
class FooState extends State<Foo> {
bool updating = false;
Future<void> _update() async {
// await something(stringFoo)
setState(() {
updating = false;
});
}
void update() {
setState(() {
updating = true;
});
_update();
}
// Dummy build, always override
@override
Widget build(BuildContext context) {
return null;
}
@override
void initState() {
super.initState();
update();
}
}
class Bar extends Foo {
final String stringBar;
Bar({Key key, String stringFoo, this.stringBar}) : super(key: key, stringFoo: stringFoo);
@override
BarState createState() => new BarState();
}
class BarState extends FooState {
@override
Widget build(BuildContext context) {
if(updating) {
return Text('Im updating: ' + widget.stringFoo);
} else {
return Text('All done!' + widget.stringBar);
}
}
}
//示例2 - 工作但手动处理状态更改
class Foo {
String stringFoo;
bool updating = false;
Widget getFoo() {
return new Text(stringFoo);
}
Future<void> _update() async {
// await something
// stringFoo = await result
updating = false;
stateChanged();
}
void update() {
updating = true;
stateChanged();
_update();
}
void stateChanged() {}
}
class Bar extends StatefulWidget {
final stringBar;
Bar({Key key, this.stringBar}) : super(key: key);
@override
BarState createState() => new BarState();
}
class BarState extends State<Bar> with Foo {
bool dummy = true;
Widget getBar() {
return new Text(widget.stringBar);
}
@override
void stateChanged() {
setState(() {
if(dummy) {
dummy = false;
} else {
dummy = true;
}
});
}
@override
Widget build(BuildContext context) {
if(updating) {
return getBar();
} else {
return getFoo();
}
}
@override
void initState() {
super.initState();
update();
}
}
答案 0 :(得分：9)
这可以使用模板来完成。
我找到了一个有效的案例，因此我将继续使用它。这是一个例子...
基类为：
class BasePage extends StatefulWidget class BasePageState<T extends BasePage> extends State<T> 请注意，要继承的类必须是公共的，因此类的名称为BasePage和BasePageState，而不是_BasePage和_BasePageState。
还要注意，BasePageState被声明为模板，以便从它们继承的状态类可以在其中传递自己的小部件。
继承的类为：
class MyHomePage extends BasePage class _MyHomePageState extends BasePageState<MyHomePage> class MyHomePage2 extends BasePage class _MyHomePageState2 extends BasePageState<MyHomePage2> counter变量和函数incrementCounter()在BasePageState类中定义，函数将计数器加1。
在_MyHomePageState2类中，我重写incrementCounter()函数并使它的计数器增加2。
我仍在测试它，所以不知道我是否会遇到一些陷阱，但到目前为止看来仍然有效。
以下是飞镖文件...
main.dart：
import 'package:flutter/material.dart';
import 'package:svipopusti/main2.dart';
import 'base_page.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'HomePage'),
);
}
}
class MyHomePage extends BasePage {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
// @override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends BasePageState<MyHomePage> {
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
FlatButton(
child: Text("Open main2"),
onPressed: () => Navigator.push(context, MaterialPageRoute(builder: (context) => MyHomePage2(title: "Homepage 2"))),
),
Text(
'You have pushed the button this many times:',
),
Text(
'$counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
main2.dart：
import 'package:flutter/material.dart';
import 'base_page.dart';
class MyHomePage2 extends BasePage {
MyHomePage2({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
// @override
_MyHomePageState2 createState() => _MyHomePageState2();
}
class _MyHomePageState2 extends BasePageState<MyHomePage2> {
@override
void incrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
counter += 2;
});
}
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
base_page.dart：
import 'package:flutter/material.dart';
class BasePage extends StatefulWidget {
BasePage({Key key}) : super(key: key);
@override
BasePageState createState() => BasePageState();
}
class BasePageState<T extends BasePage> extends State<T> {
int counter = 0;
void incrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
counter++;
});
}
@override
Widget build(BuildContext context) {
return Container();
}
}
答案 1 :(得分：4)
别。你应该从不扩展小部件。这是反模式。相反，正如flutter文档所述：
您可以通过编写小部件来构建更复杂的小部件来创建布局。
一个例子是：
class Foo extends StatefulWidget {
final Widget child;
Foo({this.child});
@override
_FooState createState() => new _FooState();
}
class _FooState extends State<Foo> {
@override
Widget build(BuildContext context) {
return new Container(
);
}
}
class Bar extends StatefulWidget {
final Widget child;
Bar({this.child});
@override
_BarState createState() => new _BarState();
}
class _BarState extends State<Bar> {
@override
Widget build(BuildContext context) {
return new Foo(
child: widget.child
);
}
}
在这种情况下，Bar没有mixin或继承。它只是将它的孩子包裹在Foo内。