Flutter LocalStorage: LateInitializationError: Field 'localStorage' has not been initialized

Question

我是 Flutter 的新手，在使用 shared_preferences 为应用程序提供自动登录功能时遇到了困难。这是它的代码。

抛出异常时，这是堆栈：

#0 本地存储（包：ui_task/loginform.dart）

#1 MyApp.build（包：ui_task/main.dart:135:8）

#2 StatelessElement.build（包：flutter/src/widgets/framework.dart:4706:28）

#3 ComponentElement.performRebuild（包：flutter/src/widgets/framework.dart:4632:15）

#4 Element.rebuild（包：flutter/src/widgets/framework.dart:4322:5）

bool? isLoginDoneBefore;
void main() {
  runApp(MyApp());
}
// ignore: must_be_immutable
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  // late bool? isLoginDoneBefore = localStorage.getBool("isLoginSuccessful");
  @override

  void initState() {
    getData();
  }

  getData() async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    isLoginDoneBefore=prefs.getBool("isLoginSuccessful");
  }


  Widget build(BuildContext context) {
    // ignore: unnecessary_null_comparison
    if(localStorage==null || isLoginDoneBefore==null){
      return MaterialApp(
        title: 'Login Form',
        theme: ThemeData(
          primarySwatch: Colors.blueGrey,
        ),
        home: LoginFormWithAutoValidation(),
      );
    }
    else {
      return MaterialApp(
        title: 'Login Form',
        theme: ThemeData(
          primarySwatch: Colors.blueGrey,
        ),
        home: isLoginDoneBefore! ? afterLogin() : LoginFormWithAutoValidation(),
      );
    }
  }
}

更新：添加最顶层的堆栈文件。这是 loginform.dart:


late SharedPreferences localStorage;

class LoginFormWithAutoValidation extends StatefulWidget {
  @override
  _LoginFormWithAutoValidationState createState() => _LoginFormWithAutoValidationState();

  // static Future init() async{
  //   localStorage = await SharedPreferences.getInstance();
  // }

}

class _LoginFormWithAutoValidationState extends State<LoginFormWithAutoValidation> {

  TextStyle style = TextStyle(fontFamily: 'Montserrat', fontSize: 20.0);

  TextEditingController _passwordController = new TextEditingController();
  TextEditingController _unameController = new TextEditingController();

  final _formKey = new GlobalKey<FormState>();
  late bool isLoginSuccessful;
  late String? _uname;
  late String? _password;
  bool _autoValidate = false;
  save() async{
    // await LoginFormWithAutoValidation.init();
    localStorage.setString('uname',_unameController.text.toString());
    localStorage.setString('password',_passwordController.text.toString());
    localStorage.setBool("isLoginSuccessful",true);
  }
  @override
  Widget build(BuildContext context) {

    return Scaffold(
      backgroundColor: Colors.blueGrey[900],
      body: Center(
        child: SingleChildScrollView(
          child: Padding(
            padding: const EdgeInsets.all(10.0),
            child: Column(
            . . . . .
            Material(
                   // login button
                            
                onPressed: () {
                    if (_formKey.currentState!.validate()) {
                        save();
                        Navigator.push(context,MaterialPageRoute(builder: (context) {
                              return afterLogin();}));
                    } else {
                            setState(() 
                             // validation error
                             _autoValidate = true;
                    });
              }

Answer 1

您在 loginform.dart 文件的顶部定义了 localStorage，但您没有使用 await SharedPreferences.getInstance(); 初始化它，这就是引发错误的原因。除此之外，我不建议将密码以明文形式存储在 shared_preferences 中（如果有的话）。它很容易被提取出来。如果您绝对必须存储它，我建议：https://pub.dev/packages/flutter_secure_storage

Flutter LocalStorage: LateInitializationError: Field 'localStorage' has not been initialized

Flutter LocalStorage: LateInitializationError: Field 'localStorage' has not been initialized

sharedpreferences

flutter