The getter 'uid' was called on null. Receiver: null Tried calling: uid Flutter Firebase

Question

i am sending userID to Profile Page from Selector Page. The error appears once and then disappears. But the app works. Debug console say the error is related with the selectorPage. I think there's a problem in the userInfo function.

here is my selectorPage: I am sending the currentUser to ProfilePage

final FirebaseAuth auth = FirebaseAuth.instance;
User1 currentUser;

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

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

class _SelectorPageState extends State<SelectorPage> {
  int _selectedIndex = 0;
  PageController _pageController;
  AuthService authService = new AuthService();

  Future<void> userInfo() async {
    print("It's work!");
    final User gcurrentUser = auth.currentUser;
    DocumentSnapshot documentSnapshot =
        await usersReference.doc(gcurrentUser.uid).get();

    if (!documentSnapshot.exists) {
      print("there's no data");
    }
    setState(() {
      currentUser = User1.fromDocument(documentSnapshot);
    });
  }

  @override
  void initState() {
    setState(() {
      userInfo();
    });
    super.initState();
    _pageController = PageController();
  }

  @override
  void dispose() {
    _pageController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SizedBox.expand(
        child: PageView(
          controller: _pageController,
          onPageChanged: (index) {
            setState(() => _selectedIndex = index);
          },
          children: <Widget>[
            HomePage(),
            ChattingPage(),
            NotificationPage(),
            ProfilePage(userProfileId: currentUser.uid),
          ],
        ),
      ),
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: _selectedIndex,
        selectedItemColor: Colors.white,
        unselectedItemColor: Colors.grey[600],
        backgroundColor: mainColor2,
        onTap: _onItemTapped,
        items: <BottomNavigationBarItem>[
          BottomNavigationBarItem(
              label: '', icon: Icon(Icons.home), backgroundColor: mainColor2),
          BottomNavigationBarItem(
              label: '', icon: Icon(Icons.chat), backgroundColor: mainColor2),
          BottomNavigationBarItem(
              label: '',
              icon: Icon(Icons.new_releases),
              backgroundColor: mainColor2),
          BottomNavigationBarItem(
              label: '',
              icon: Icon(Icons.account_circle_outlined),
              backgroundColor: mainColor2),
        ],
      ),
    );
  }

  void _onItemTapped(int index) {
    setState(() {
      _selectedIndex = index;
      userInfo();
      _pageController.animateToPage(index,
          duration: Duration(milliseconds: 500), curve: Curves.easeOut);
    });
  }
}

and Profile Page:

class ProfilePage extends StatefulWidget {
  final String userProfileId;
  ProfilePage({this.userProfileId});

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

class _ProfilePageState extends State<ProfilePage> {
  AuthService authService = new AuthService();

  final String currentOnlineUserId = currentUser?.uid;

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

  createProfileTopView() {
    return FutureBuilder(
        future: usersReference.doc(widget.userProfileId).get(),
        builder: (context, dataSnapshot) {
          if (!dataSnapshot.hasData) {
            return Center(
              child: Lottie.asset('assets/images/1.json'),
            );
          }

          User1 user = User1.fromDocument(dataSnapshot.data);

          return Padding(
            padding: context.paddingLow,
            child: Column(
              children: [
                Row(
                  children: [
                    CircleAvatar(
                      radius: 45.0,
                      backgroundColor: Colors.grey,
                      backgroundImage:
                          CachedNetworkImageProvider(user.photoLink),
                    ),
                    Expanded(
                        child: Column(
                      children: [
                        Row(
                          mainAxisSize: MainAxisSize.max,
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: [
                            createColumns("Gönderi", 0),
                            createColumns("Takipçi", 0),
                            createColumns("Takip", 0),
                          ],
                        ),
                        Row(
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: [createButton()],
                        ),
                      ],
                    ))
                  ],
                ),
              ],
            ),
          );
        });
  }

  Column createColumns(String title, int count) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(
          count.toString(),
          style: TextStyle(
              fontWeight: FontWeight.w300, color: Colors.white, fontSize: 20.0),
        ),
        Container(
          margin: EdgeInsets.only(top: 5.0),
          child: Text(
            title,
            style: TextStyle(
                fontWeight: FontWeight.w300,
                color: Colors.white,
                fontSize: 16.0),
          ),
        )
      ],
    );
  }

  createButton() {
    bool ownProfile = currentOnlineUserId == widget.userProfileId;
    if (ownProfile) {
      return createButtonTitleAndFunction(
          title: "Profili düzenle", performFunction: editUserProfile);
    }
  }

  createButtonTitleAndFunction({String title, Function performFunction}) {
    return Container(
      padding: EdgeInsets.only(top: 3.0),
      child: FlatButton(
        onPressed: () {},
        child: Container(
          width: 245.0,
          height: 26.0,
          child: Text(
            title,
            style: TextStyle(
              fontWeight: FontWeight.w300,
              color: Colors.grey,
            ),
          ),
          alignment: Alignment.center,
          decoration: BoxDecoration(
            color: Colors.black,
            border: Border.all(color: Colors.grey),
            borderRadius: BorderRadius.circular(6.0),
          ),
        ),
      ),
    );
  }

  editUserProfile() {
    Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) =>
                EditProfilePage(currentOnlineUserId: currentOnlineUserId)));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        backgroundColor: mainColor,
        appBar: AppBar(
          backgroundColor: mainColor2,
          title: Text(
            "Profil",
            style: TextStyle(fontWeight: FontWeight.w300),
          ),
          actions: [
            IconButton(
                icon: Icon(Icons.logout),
                onPressed: () {
                  authService.signOut();
                  Navigator.pushReplacement(context,
                      MaterialPageRoute(builder: (context) => LoginPage()));
                })
          ],
        ),
        body: ListView(
          children: [
            createProfileTopView(),
          ],
        ));
  }
}

Also my UserModal:

class User1 {
  final String bio;
  final String email;
  final String linkedinLink;
  final String name;
  final String password;
  final String photoLink;
  final String uid;
  final String university;
  final String username;

  User1({
    this.bio,
    this.email,
    this.linkedinLink,
    this.name,
    this.password,
    this.photoLink,
    this.uid,
    this.university,
    this.username,
  });

  factory User1.fromDocument(DocumentSnapshot docx) {
    return User1(
      bio: docx['bio'],
      email: docx['email'],
      linkedinLink: docx['linkedinLink'],
      name: docx['name'],
      password: docx['password'],
      photoLink: docx['photoLink'],
      uid: docx.id,
      university: docx['university'],
      username: docx['username'],
    );
  }
}

Answer 1

Most likely the problem is here:

ProfilePage(userProfileId: currentUser.uid),

You're trying to pass currentUser.uid to the ProfilePage, but initially the currentUser is going to be null. So that explains the error.

The solution is to only render the ProfilePage when there is a current user, for example with:

currentUser != null ? ProfilePage(userProfileId: currentUser.uid) : Text("Loading user data..."),