flutter - setState()在构造函数中调用，可以从另一个类更改窗口小部件的状态吗？

Question

当我尝试通过定义用于设置状态的自定义函数来更改窗口小部件的状态时出现此错误，然后从我创建的新类中调用该函数。

setState() called in constructor: _MyHomePageState#da7cc(lifecycle state: created, no widget, not mounted)

主页:

import 'package:flutter/material.dart';
import 'package:ed_cell/auth_service.dart';
import 'package:flutter/scheduler.dart';

Widget authStatus = Text('Welcome');

class MyHomePage extends StatefulWidget {
  _MyHomePageState myHomePageState= new _MyHomePageState();
  @override
  _MyHomePageState createState() => myHomePageState;
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return ListView(
      children: [
        Container(
          decoration: BoxDecoration(
              color: Colors.white, borderRadius: BorderRadius.circular(10)),
          height: 575,
          child: Row(
            children: <Widget>[
              Column(
                children: [
                  Expanded(
                    child: Image.asset(
                      'assets/images/rocket.png',
                    ),
                  ),
                ],
              ),
              Expanded(
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  children: [
                    Text(
                      'U create\nWe support',
                      style:
                          TextStyle(fontSize: 80, fontWeight: FontWeight.bold),
                    ),
                    authStatus,
                  ],
                ),
              ),
            ],
          ),
        ),
      ],
    );
  }

  void onAuthChange() {
     var x=AuthService().status;
    if (AuthService().status == 'Sucessful Sign In') {
      setState(()  {
        authStatus = Text(
          'Welcome',
          style: TextStyle(color: Colors.grey, fontSize: 50),
        );
        print(x);
      });
      print('object'+x);
    } else {
      setState(()  {
        authStatus = RaisedButton(
          onPressed: null,
          color: Colors.deepOrange,
          child: Text(
            'Join Now',
            style: TextStyle(color: Colors.white, fontWeight: FontWeight.bold),
          ),
        );
      });
    }
  }
}

AuthService:

import 'package:firebase_auth/firebase_auth.dart';
import 'package:ed_cell/home_page.dart';

class AuthService{
  String status;

  signIn(email,password){
    FirebaseAuth.instance.signInWithEmailAndPassword(email: email, password: password).then((user){
      print('Signed In '+user.user.uid);
      status='Sucessful Sign In';
    }).catchError((e){
      status='Failure in Sign In';
      print(e);
    });
    MyHomePage().myHomePageState.onAuthChange();
  }
}

Answer 1

该错误与HomePage尚未插入小部件树有关。您可以按照正确的方法从另一个类调用setState，但是HomePage窗口小部件必须位于窗口小部件树中的某个位置，才能执行setState。