我已经 "null check opreator used on a null value"

Question

我一直收到错误“null chack opreator used on a null value” 每当我尝试使用提供程序从我的 firestore 数据库中提取值并更改通知程序时

这是我的 user_provider.dart

    import 'package:flutter/widgets.dart';
    import 'package:test_app/models/user.dart';
    import 'package:test_app/resources/auth_methods.dart';
    
    class UserProvider with ChangeNotifier {
      User? _user;
      final AuthMethods _authMethods = AuthMethods();
    
      User get getUser => _user!;
    
      Future<void> refreshUser() async {
        User user = await _authMethods.getUserDetails();
        _user = user;
        notifyListeners();
      }
    }

这是我的 home.dart 我从 firestore 中提取数据的地方

    import 'package:bottom_navy_bar/bottom_navy_bar.dart';
    import 'package:cloud_firestore/cloud_firestore.dart';
    import 'package:firebase_auth/firebase_auth.dart';
    import 'package:flutter/material.dart';
    import 'package:provider/provider.dart';
    import 'package:test_app/components/background.dart';
    import 'package:test_app/providers/user_provider.dart';
    import 'package:test_app/models/user.dart' as model;
    
    // import 'dart:html';
    
    class Home extends StatefulWidget {
      const Home({Key? key}) : super(key: key);
    
      @override
      State<Home> createState() => _HomeState();
    }
    
    class _HomeState extends State<Home> {
      @override
      void initState() {
        super.initState();
        addData();
      }
    
      addData() async {
        UserProvider _userProvider =
            Provider.of<UserProvider>(context, listen: false);
        await _userProvider.refreshUser();
      }
    
      @override
      Widget build(BuildContext context) {
        model.User? user = Provider.of<UserProvider>(context).getUser;
        
        return Scaffold(body: Text(user.email),);
      }
    }

这是我的 main.dart incase

import 'dart:ffi';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:test_app/pages/home.dart';
import 'package:test_app/pages/login.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:test_app/pages/signup.dart';
import 'package:test_app/providers/user_provider.dart';
import 'package:test_app/utilis/routes.dart';

void main() async {
  // ignore: prefer_const_constructors
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(
          create: (_) => UserProvider(),
        )
      ],
      child: MaterialApp(
          // home: Home(),
          debugShowCheckedModeBanner: false,
          themeMode: ThemeMode.dark,
          darkTheme: ThemeData(brightness: Brightness.light),
          theme: ThemeData(
              primarySwatch: Colors.deepPurple,
              fontFamily: GoogleFonts.mcLaren().fontFamily,
              appBarTheme: AppBarTheme(
                color: Colors.white,
                elevation: 0.0,
                iconTheme: IconThemeData(color: Colors.black),
              )),
          // ignore: prefer_const_constructors
          home: StreamBuilder(
              stream: FirebaseAuth.instance.authStateChanges(),
              builder: (context, snapshot) {
                if (snapshot.connectionState == ConnectionState.active) {
                  // Checking if the snapshot has any data or not
                  if (snapshot.hasData) {
                    // if snapshot has data which means user is logged in then we check the width of screen and accordingly display the screen layout
                    return const Home();
                  } else if (snapshot.hasError) {
                    return const Login();
                  }
                }

                // means connection to future hasnt been made yet
                if (snapshot.connectionState == ConnectionState.waiting) {
                  return const Center(
                    child: CircularProgressIndicator(),
                  );
                }
                return const Login();
              })),
    );
  }
}

我的调试控制台

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY 

╞═══════════════════════════════════════════════════════════
The following _CastError was thrown building Home(dirty, dependencies:
[_InheritedProviderScope<UserProvider?>], state: _HomeState#17895):
Null check operator used on a null value

The relevant error-causing widget was:
  Home Home:file:///C:/Users/abc/Desktop/flutter/test_app/lib/main.dart:53:34

When the exception was thrown, this was the stack:
#0      UserProvider.getUser (package:test_app/providers/user_provider.dart:9:28)
#1      _HomeState.build (package:test_app/pages/home.dart:36:59)
#2      StatefulElement.build (package:flutter/src/widgets/framework.dart:4870:27)
#3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4754:15)
#4      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#5      Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#6      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4735:5)
#7      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4919:11)
#8      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4729:5)
#9      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3790:14)
#10     Element.updateChild (package:flutter/src/widgets/framework.dart:3524:20)
#11     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#12     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#13     Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#14     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2659:19)
#15     WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:882:21)
#16     RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:363:5)
#17     SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1144:15)
#18     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1081:9)
#19     SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:862:7)
(elided 11 frames from class _RawReceivePortImpl, class _Timer, dart:async, and dart:async-patch)

我的应用程序运行正常，但在打开之前它显示了一个红屏，其中错误空检查运算符用于空值，一秒钟后它熄灭并继续工作，但调试在调试控制台中显示以下错误

Answer 1

你应该写User get getUser => _user ?? User();

而不是User get getUser => _user!;

在my user_provider.dart

或者你可以这样写User _user = User();

而不是User? _user;

我已经 "null check opreator used on a null value"

i've been getting "null check opreator used on a null value"

provider

null

dart

firebase

flutter