我弹出 1 个错误，但是当我尝试运行该应用程序时，它说我有所有其他错误

Posted 2023-02-23

【中文标题】我弹出 1 个错误，但是当我尝试运行该应用程序时，它说我有所有其他错误

【英文标题】：I have 1 error popping up but When I try to run the app it says I have all of these other errors that are wrong

【发布时间】：2022-01-18 05:32:30

【问题描述】：

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import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:time_trackerpractice/app/sign_in/home_page.dart';
import 'package:time_trackerpractice/app/sign_in/sign_in_page.dart';
import 'package:time_trackerpractice/services/auth.dart';

class LandingPage extends StatefulWidget 
  const LandingPage(Key key, this.auth) : super(key: key);
  final AuthBase auth;

  @override
  _LandingPageState createState() => _LandingPageState();



class _LandingPageState extends State<LandingPage> 

  User _user;

  @override
  void initState() 
    // TODO: implement initState
    super.initState();

    _updateUser(widget.auth.currentUser);
  


  void _updateUser(User user) 
    setState(() 
      _user = user;
    );
  

  

  @override
  Widget build(BuildContext context) 
   return StreamBuilder<User>(
     stream: widget.auth.authStateChanges(),
     builder: (context,snapshot)
     if(snapshot.connectionState == ConnectionState.active)
       final User user =snapshot.data;
       if(user == null)
         return SignInPage(
           auth: widget.auth,
           onSignIn: _updateUser,
         );
       
       return HomePage(
           auth: widget.auth,
           onSignOut: => _updateUser(null),
       );
     

       return Scaffold(
       body:Center(
       child: CircularProgressIndicator(),
       );
       );

     ,
   );

我一直在学习颤振课程，并且在我为应用程序键入的代码上弹出 1 个错误，但是当我尝试运行应用程序时，它说我有所有其他错误的错误。这个是唯一出现的错误和分号onSignOut: => _updateUser(null)，所以我不知道我错了。但这些是下面弹出的错误：

lib/app/sign_in/landing_page.dart:38:38: Error: Can't find '' to match ''.
Widget build(BuildContext context) 
                                   ^
lib/app/sign_in/landing_page.dart:16:52: Error: Can't find '' to match ''.
class _LandingPageState extends State<LandingPage> 
                                                   ^
lib/app/sign_in/landing_page.dart:52:23: Error: Expected an identifier, but got '=>'.
Try inserting an identifier before '=>'.
       onSignOut: => _updateUser(null),
                  ^^
lib/app/sign_in/landing_page.dart:52:26: Error: Expected ',' before this.
       onSignOut: => _updateUser(null),
                     ^^^^^^^^^^^
lib/app/sign_in/landing_page.dart:52:26: Error: Place positional arguments before named arguments.
Try moving the positional argument before the named arguments, or add a name to the argument.
       onSignOut: => _updateUser(null),
                     ^^^^^^^^^^^
lib/app/sign_in/landing_page.dart:52:26: Error: Expected named argument.
           onSignOut: => _updateUser(null),
                         ^
lib/app/sign_in/landing_page.dart:50:23: Error: No named parameter with the name '#2'.

【参考方案1】：

您有两个错误，一个是您没有关闭方法，请在代码末尾添加此行：

应该是这样的：

 ...
 return Scaffold(
       body:Center(
       child: CircularProgressIndicator(),
       );
       );

     ,
   );
 

之所以需要这样做是因为您必须同时关闭构建和小部件类

class _LandingPageState extends State<LandingPage> 

  @override
  Widget build(BuildContext context) 
    // some code
   // <--- you missed this
 // <--- you also missed this one, so you must add two  at the end of the file

第二个错误，你忘记了lambda函数上的括号：

从这里：

onSignOut: => _updateUser(null),

到这里：

onSignOut: () => _updateUser(null),

如果您不了解 lambda 是什么，请查看以下资源：https://dart.dev/guides/language/language-tour#anonymous-functions

【讨论】：

感谢您的帮助。我真的很感激。它帮助了我很多