Flutter中async...await以及无状态和有状态的widget

1、async...await 返回的是Future，后面可以接then()

import 'package:flutter/material.dart';

main(){
  renderSome();
}

request() async{
  await Future.delayed(const Duration(seconds: 2));
  return "response";
}

doSomething() async{
  var result =  await request();
  result = "OK response";
  return result;
}

renderSome(){
  doSomething().then((value){
    debugPrint("result:$value");
  });
}

2、无状态和有状态的widget

import 'package:flutter/material.dart';

main(){
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(
          title: const Text("无状态Widget"),
          centerTitle: true,
        ),
        body:  const DemoStateWidget(),
      ),
    );
  }
}

class DomeWidget extends StatelessWidget {
  const DomeWidget(this.text,{Key? key}) : super(key: key);

  final String text;

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.white,
      child: Text(text),
    );
  }
}

class DemoStateWidget extends StatefulWidget {
  const DemoStateWidget({Key? key}) : super(key: key);

  @override
  State<DemoStateWidget> createState() => _DemoStateWidgetState();
}

class _DemoStateWidgetState extends State<DemoStateWidget> {

    String? text;

    @override
    void initState() {
    super.initState();

    //延迟两秒改变text数值
    Future.delayed(const Duration(seconds: 2),(){
      setState(() {
        text = "这就变了数值";
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Text(text ?? "有状态的widget");
  }

  @override
  void dispose() {
    super.dispose();
    debugPrint("dispose()");
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    debugPrint("didChangeDependencies()");
  }
}