问如何运行firstapp flutter 1.5

EN

error: The function 'MyApp' isn't defined. (undefined_function at [flutter_app007] lib\main.dart:3)
error: 'MaterialApp' isn't a function. (invocation_of_non_function at [flutter_app007] lib\main.dart:8)
error: 'Scaffold' isn't a function. (invocation_of_non_function at [flutter_app007] lib\main.dart:10)
error: 'AppBar' isn't a function. (invocation_of_non_function at [flutter_app007] lib\main.dart:11)

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Welcome to Flutter',
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Welcome to Flutter'),
        ),
        body: const Center(
          child: const Text('Hello World'),
        ),
      ),
    );
  }
}