Flutter - How to return current user from Firestore

问题

Trying to retrieve the authenticated user details from the existing Firestore user document, I get the following error:

The getter 'uid' was called on null

my code is as follows:

    class SideDrawer extends StatelessWidget {
      const SideDrawer({Key key, this.user}) : super(key: key);
      final FirebaseUser user;

      @override
      Widget build(BuildContext context) {
        return ......
              ......
              userPanel(context),
              ......
      }

      Widget userPanel(BuildContext context) {
        return new Padding(
          padding: const EdgeInsets.only(top: 10.0),
          child: new DrawerHeader(
            child: StreamBuilder<DocumentSnapshot>(
              stream: Firestore.instance
                  .collection('users')
                  .document(user.uid)
                  .snapshots(),
              builder:
                  (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
                if (snapshot.hasError) {
                  return Text('Error: ${snapshot.error}');
                } else if (snapshot.hasData) {
                  return userName(snapshot.data);
                }
                return LinearProgressIndicator();
              },
            ),
          ),
        );
      }
    }

Text userName(DocumentSnapshot snapshot) {
  if (snapshot.data == null) {
    return Text('no data set in the user document in firestore');
  } else {
    return snapshot.data['name'];
  }
}

sending user from login page:

  void signIn() async {
    if(_formKey.currentState.validate()){
      _formKey.currentState.save();
      try{
        FirebaseUser user = await FirebaseAuth.instance.signInWithEmailAndPassword(email: _email, password: _password);
        Navigator.push(context, MaterialPageRoute(builder: (context) => HomePage(user: user)));
      }catch(e){
        print(e.message);
      }
    }
  }
}

and here is my Home page:

class HomePage extends StatelessWidget {
  const HomePage({Key key, this.user}) : super(key: key);
  final FirebaseUser user;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      drawer: SideDrawer(),
    );
  }
}

Guessing this is an asynchronous programming issue, I did some search on it and found few solutions using "Future" object but could not figure out how to implement it in a correct way, any help please ?

回答1:

If you are using Future I guess when you call SideDrawer the user is null, so you have to add a validation before you can use 'user' object.

 Widget userPanel(BuildContext context) {
            return new Padding(
              padding: const EdgeInsets.only(top: 10.0),
              child:  user != null ? DrawerHeader(
                child: StreamBuilder<DocumentSnapshot>(
                  stream: Firestore.instance
                      .collection('users')
                      .document(user.uid)
                      .snapshots(),
                  builder:
                      (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
                    if (snapshot.hasError) {
                      return Text('Error: ${snapshot.error}');
                    } else if (snapshot.hasData) {
                      return userName(snapshot.data);
                    }
                    return LinearProgressIndicator();
                  },
                ),
              ) : Center(child: CircularProgressIndicator(),)
            );

        }

Pass the user object on your SideDrawer widget from HomePage

  SideDrawer(user: user),

Also fix this line:

 return snapshot.data['name'];

It should be :

  return Text(snapshot.data['name']);

来源：https://stackoverflow.com/questions/54244652/flutter-how-to-return-current-user-from-firestore