列表更新Stateful Widget中的变量以及局部变量

import 'package:flutter/material.dart';

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  String _text = 'Initial Value';

  void _updateText() {
    setState(() {
      _text = 'Updated Value';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(_text),
            RaisedButton(
              onPressed: _updateText,
              child: Text('Update'),
            ),
          ],
        ),
      ),
    );
  }
}