我在第一个屏幕中存储了一个字符串，然后通过以下代码从第二个屏幕中检索了存储的值

第1页：

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:trial/class2.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String _email = '';

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

  _loadCounter() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _email = (prefs.getString('email') ?? '');
    });
  }

  _incrementCounter() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _email = "a@gmail.com";
    });
    prefs.setString('email', _email);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("title"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              '$_email',
            ),
            new RaisedButton(
              child: new Text("next2"),
              onPressed: () {
                Navigator.push(context,
                    new MaterialPageRoute(builder: (context) => new Next()));
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        child: Icon(Icons.add),
      ),
    );
  }
}

第2页：

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
String _email='';
class Next extends StatefulWidget {
  @override
  _NextState createState() => _NextState();
}

class _NextState extends State<Next> {
    @override
  void initState() {
    super.initState();
    _loadCounter();
  }

  _loadCounter() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _email = (prefs.getString('email')??'');
    });
  }
  @override
  Widget build(BuildContext context) {

    return Container(
      child: new Text("read value from sharepreference is:"+_email),
    );
  }
}