Why can't I reach the variable inside an initState in flutter?

问题

I am trying to use a variable that I got from firestore by using a void finction and when I print it in the same function or another function it gets it but when I use it in an initState it gives me null HELP! the var I want is userType. code : getuserData form firebase:

void getUserData() async {
    try {
      firestoreInstance
          .collection('Users')
          .document(usernameController.text)
          .get()
          .then((value) {
        setState(() {
          email = (value.data)['email'];
          password = (value.data)['password'];
          gender = (value.data)['gender'];
          username = (value.data)['username'];
          userType = (value.data)['userType'];
        });
      });
    } catch (e) {
      print(e.toString);
    }
  }

and the initstate :

void initState() {
    super.initState();
    FirebaseAuth.instance.currentUser().then(
      (result) {
        if (result != null) {
          print(userType);
          print(result);
          if (userType == 'Admin') {
            Navigator.pushReplacementNamed(context, '/AdminPage');
          }
          if (userType == 'Student') {
            Navigator.pushReplacementNamed(context, '/StudentPage');
          }
          if (userType == 'Teacher') {
            Navigator.pushReplacementNamed(context, '/TeacherPage');
          }
        } else {
          showDialog(
            context: context,
            builder: (BuildContext context) {
              return AlertDialog(
                title: Text('Error'),
                content: Text(
                    'Please make sure that you have an internet connection'),
                actions: [
                  FlatButton(
                    child: Text("Ok"),
                    onPressed: () {
                      Navigator.of(context).pop();
                    },
                  )
                ],
              );
            },
          );
        }
      },
    );
  }

calling getuserdata:

child: Center(
                      child: Container(
                        width: 250,
                        height: 50,
                        child: FlatButton(
                          onPressed: () => {getUserData(), login()},
                          child: Text(
                            "Login",
                            style: TextStyle(
                                color: Colors.deepOrangeAccent,
                                fontSize: 20,
                                fontWeight: FontWeight.bold),
                          ),
                          shape: RoundedRectangleBorder(
                            borderRadius: BorderRadius.circular(25.0),
                          ),
                        ),
                      ),
                    ),

回答1:

Let's find out why you have userType == null in initState()...

Timeline of what is going on

when widget state created initState() runs once before build() is first time called
when build() done you have Button with onPressed callback configured
user clicks that Button and function getUserData() is called
because function is asyncronous we have result somewhere in future
on result setState() is called and userType fullfilled with some data

And if no errors occured now you have userType != null

PS if you describe desired behavior - add commments, we'll try to reach result you want

来源：https://stackoverflow.com/questions/62691949/why-cant-i-reach-the-variable-inside-an-initstate-in-flutter

标签

Flutter

google-cloud-firestore