keep getting "Null check operator used on a null value" error. i've checked my code 1-CodePudding

keep getting "Null check operator used on a null value" error actually im trying to use providers to get values from database and use em in my app but im stuck at this i checked my code in every single way but still i keep getting this error

:lib\providers\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();
  }
}

lib\pages\home.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/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: Center(
        child: Text("this is homepage"),
      ),
    );
  }
}

debug snippet

#15     WidgetsBinding.drawFrame
package:flutter/…/widgets/binding.dart:882
#16     RendererBinding._handlePersistentFrameCallback
package:flutter/…/rendering/binding.dart:363
#17     SchedulerBinding._invokeFrameCallback
package:flutter/…/scheduler/binding.dart:1145
#18     SchedulerBinding.handleDrawFrame
package:flutter/…/scheduler/binding.dart:1082
#19     SchedulerBinding._handleDrawFrame
package:flutter/…/scheduler/binding.dart:996
#23     _invoke (dart:ui/hooks.dart:150:10)
#24     PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:270:5)
#25     _drawFrame (dart:ui/hooks.dart:114:31)
(elided 3 frames from dart:async)

idk what the problem actually im new to flutter and dart i've using python for my whole life

CodePudding user response：

refreshUser is a future and it sets _user but because you're calling getUser IMMEDIATELY build method, which basically returns _user as a non-null value, the error would be thrown.

Try this:

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();
  }
}

And your _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: Center(
        child: Text("this is homepage"),
      ),
    );
  }
}