SharePreference

知识点：
当BuildContext在Scaffold之前时，调用Scaffold.of(context)会报错。这时可以通过Builder Widget来解决：

异步操作：

save() async{
      SharedPreferences prefs = await SharedPreferences.getInstance();
      prefs.setString(mUserName, _userNameController.value.text.toString());//第一个参数是key,第二个参数是value;
    }

    Future<String> get() async {
      var userName;
      SharedPreferences prefs = await SharedPreferences.getInstance();
      userName = prefs.getString(mUserName);
      return userName;
    }

Future<String> userName = get();
                        userName.then((String userName) {
                          Scaffold.of(context).showSnackBar(
                              SnackBar(content: Text("数据获取成功：$userName")));
                        });

import 'dart:async';

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

void main() {
  runApp(MaterialApp(home: MyApp()));
}



class MyApp extends StatelessWidget {
  final String mUserName = "userName";
  final _userNameController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    save() async{
      SharedPreferences prefs = await SharedPreferences.getInstance();
      prefs.setString(mUserName, _userNameController.value.text.toString());
    }

    Future<String> get() async {
      var userName;
      SharedPreferences prefs = await SharedPreferences.getInstance();
      userName = prefs.getString(mUserName);
      return userName;
    }

    return Builder(builder: (BuildContext context) {
      return Scaffold(
        appBar:  AppBar(
          title:  Text("SharedPreferences"),
        ),
        body:  Center(
          child: new Builder(builder: (BuildContext context){
            return
              Column(
                children: <Widget>[
                  TextField(
                    controller: _userNameController,
                    decoration:  InputDecoration(
                        contentPadding: const EdgeInsets.only(top: 10.0),
                        icon:  Icon(Icons.perm_identity),
                        labelText: "请输入用户名",
                        helperText: "注册时填写的名字"),
                  ),
                  RaisedButton(
                      child: Text("存储"),
                      onPressed: () {
                        save();
                        Scaffold.of(context).showSnackBar(
                            SnackBar(content:  Text("数据存储成功")));
                      }),
                  RaisedButton(
                      child: Text("获取"),
                      onPressed: () {
                        Future<String> userName = get();
                        userName.then((String userName) {
                          Scaffold.of(context).showSnackBar(
                              SnackBar(content: Text("数据获取成功：$userName")));
                        });
                      }),
                ],
              );
          }),
        ),
      );
    });
  }
}




下面这个示例是我根据上面的例子自己写的：

import 'package:flutter/material.dart';
import 'dart:async';
import 'package:shared_preferences/shared_preferences.dart';

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

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

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  TextEditingController _textEditingController=TextEditingController();
  saveData() async {
    SharedPreferences pref = await SharedPreferences.getInstance();
    pref.setString('keyvalue', _textEditingController.text);
  }

  Future<String> getData()async{
    SharedPreferences pref=await SharedPreferences.getInstance();
    var backData;
    backData=pref.getString('keyvalue');
    return backData;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(''),
      ),
      body: Builder(builder: (context) {
        return Center(
          child: Column(
            children: <Widget>[
              TextField(
                controller: _textEditingController,
                decoration: InputDecoration(
                  hintText: '请输入数据：',
                  border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(28)),
                ),
              ),
              RaisedButton(
                  child: Text('保存'),
                  onPressed: () {
                    saveData();
                    Scaffold.of(context).showSnackBar(SnackBar(content: Text('保存数据${_textEditingController.text}',),),);
                  }),
              RaisedButton(
                  color: Colors.greenAccent,
                  child: Text("获取"),
                  onPressed: () {
                    Future<String> userName = getData();
                    userName.then((String value) {
                      Scaffold.of(context).showSnackBar(
                          SnackBar(content: Text("数据获取成功：$value")));
                    });
                  }),
            ],
          ),
        );
      }),
    );
  }
}