创建类型为ScaffoldState的GlobalKey，以确保您以正确的Scaffold为目标，以在其上显示SnackBar。
将目标脚手架的密钥设置为您创建的密钥。
在initState（）函数中，使用WidgetsBinding类和addPostframeCallback在构建布局时执行代码。在回叫中显示您的SnackBar。
import 'package:flutter/material.dart';void main() => runApp(new MyApp());class MyApp extends StatelessWidget { // This widget is the root of your application. @override Widget build(BuildContext context) { return new MaterialApp( title: 'Flutter Demo', theme: new ThemeData( primarySwatch: Colors.blue, ), home: new MyHomePage(title: 'Flutter Demo Home Page'), ); }}class MyHomePage extends StatefulWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override _MyHomePageState createState() => new _MyHomePageState();}class _MyHomePageState extends State<MyHomePage> { var _scaffoldKey = GlobalKey<ScaffoldState>(); @override void initState() { super.initState(); WidgetsBinding.instance.addPostframeCallback((_) => _scaffoldKey.currentState.showSnackBar(SnackBar(content: Text('Welcome User')))); } @override Widget build(BuildContext context) { return new Scaffold( key: _scaffoldKey, appBar: new AppBar( title: new Text(widget.title), ), body: new Center( child: new Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[], ), ), ); }}
