Flutter提示之Navigator operation requested with a context that does not include a Navigator.

void main() {
  runApp(MyApp1());
}
class MyApp1 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'open url',
      home: Scaffold(
          appBar: AppBar(
            title: Text('hello flutter'),
          ),
          body: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            mainAxisSize: MainAxisSize.min,
            children: <Widget>[
              FlatButton(
                child: Text("go to new page"),
                textColor: Colors.blue,
                onPressed: () {
                    Navigator.push(context, MaterialPageRoute(
                      builder:(context) => NewPage()));
                },
              ),
            ],
          ),
      ),
    );
  }
}
class NewPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
      return Scaffold(
        appBar: AppBar(
            title: Text("hello word"),
        ),
        body: Center(
           child: Text("this is new page"),
        ),
      );
  }
}

void main() {
    runApp(MaterialApp(
    title: "Navigation basics",
    home: MyApp1(),
  ));
}