flutter_tracker/lib/pages/login_page.dart

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

class LoginPage extends StatefulWidget {
  const LoginPage({Key key}) : super(key: key);

  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  final TextEditingController _usernameController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();
  final _formKey = GlobalKey<FormState>();

  String _username;
  String _password;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: Text('登录')),
        body: Form(
          key: _formKey,
          child: Column(
            children: <Widget>[
              TextFormField(
                controller: _usernameController,
                decoration: InputDecoration(
                  labelText: '用户名',
                  hintText: '请输入用户名',
                ),
                validator: (value) {
                  if (value.isEmpty) {
                    return '用户名不能为空';
                  }
                  return null;
                },
                onSaved: (value) {
                  _username = value;
                },
              ),
              TextFormField(
                controller: _passwordController,
                decoration: InputDecoration(
                  labelText: '密码',
                  hintText: '请输入密码',
                ),
                obscureText: true,
                validator: (value) {
                  if (value.isEmpty) {
                    return '密码不能为空';
                  }
                  return null;
                },
                onSaved: (value) {
                  _password = value;
                },
              ),
              RaisedButton(
                child: Text('登录'),
                onPressed: () {
                  login();
                },
              ),
            ],
          ),
        ));
  }

  void loadData() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    String username = prefs.getString('username');
    String password = prefs.getString('password');
    if (username != null && password != null) {
      _usernameController.text = username;
      _passwordController.text = password;
    }
  }

  void login() async {
    if (_formKey.currentState.validate()) {
      _formKey.currentState.save();
      SharedPreferences prefs = await SharedPreferences.getInstance();
      prefs.setString('username', _username);
      prefs.setString('password', _password);
      Navigator.of(context).pushReplacementNamed('/home');
    }
  }
}