flutter - 如何在 flutter 中实现可观察的消费者(听众)

Question

我还在学习 flutter 。以下是本教程中的代码。当我调用Authservice配置文件时，它返回Observable<Map<String, dynamic>>。如何获取其中的数据以进行显示。

这是我到目前为止所做的事情，但是它返回了整个块，但我想分开获取每一对。例如电子邮件，姓名等。

AuthService.profile.listen((value){
    print(value);
});
//This is my solution so far
---------------------------------------------------------------------

//This is my code

import 'package:firebase_auth/firebase_auth.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:rxdart/rxdart.dart';

class AuthService {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final Firestore _db = Firestore.instance;
  final GoogleSignIn _googleSignIn = GoogleSignIn();

  Future<FirebaseUser> get getUser => _auth.currentUser();
  //Stream<FirebaseUser> get user => _auth.onAuthStateChanged;

  Observable<FirebaseUser> user; //firebase user
  Observable<Map<String, dynamic>> profile; //custom user data in firestore
  PublishSubject loading = PublishSubject(); // Push new value manulay

  AuthService() {
    user = Observable(_auth.onAuthStateChanged);
    profile = user.switchMap((FirebaseUser u) {
      if (u != null) {
        return _db
            .collection('users')
            .document(u.uid)
            .snapshots()
            .map((snap) => snap.data);
      } else {
        return Observable.just({});
      }
    });
  }```

Answer 1

这是一个有关如何在Dart中访问 类型的Map的简单示例:

foo() {
    Map<String, dynamic> user = {
      "uid":7,
      "username": "nasser",
    };

    print('${user.toString()}'); // {uid: 7, username: nasser}
    print('${user['uid']}'); // 7

    // You can loop inside Map and do whatever 
    // you want with the key and the value; print them,
    // Or create a UserModel object from them..:
    user.forEach((key, value) => print('$key: $value'));
    // forEach's output:
    // uid: 7
    // username: nasser
} 

更新问题的具体情况:

根据此代码:

AuthService.profile.listen((value){
    print(value);
});

您正在访问Class本身，它将无法正常工作(除非功能'profile'是静态的，这不是此处)，因此 首先需要在使用之前从“AuthService”类创建一个实例。而且，由于您需要在所有应用程序中使用相同的对象，因此，需要在内具有“AuthService”类的文件的末尾创建一个共享对象 ，请参阅并阅读评论:

class AuthService {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final Firestore _db = Firestore.instance;
  final GoogleSignIn _googleSignIn = GoogleSignIn();
  //..
  //..
} // THIS IS THE CLOSING OF "class AuthService {"

// Add this at the end of the file that you are 
// saving "AuthService" class in, SO YOU WILL BE CREATING 
// A SHARED OBJECT(KINDA BLOC) that you can access from 
// other classes without creating a new instance, just 
// by importing "AuthService class" file.
// This thing has a nickname called 'Singleton' but needs some
// little work to be a perfect Singleton, but it's enough here:
final authService = AuthService(); 

现在可以使用“authService”对象。因此，将在小部件中使用用户配置文件数据(例如homeScreen或)，需要导入包含“AuthService类”和 final authService = AuthService();的文件。

然后随意访问已创建的 uthService对象 (没有的 uthService类，请参阅小写字母)，并通过import 'auth_service.dart';在“HomeScreen”中将其使用，请参见以下代码和注释:

// Import AuthService class, I assume that this is the file name and location
import 'auth_service.dart';

class HomeScreen extends StatefulWidget {
  @override
  HomeScreenState createState() => HomeScreenState();
}

class HomeScreenState extends State<HomeScreen> {
  // Define a var with same type as the Observable to store its data:
  Map<String, dynamic> _userProfile;

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

    // Listen to Observable which called "profile" and once this
    // Observable get updated, it will update "_userProfile" too,
    // setState here is important, otherwise you will need a streamBuilder
    // to see the changes on screen:
    authService.profile.listen((v) => setState(() => _userProfile = v));
  }

  @override
  Widget build(BuildContext context) {

    // WAIT TILL THE FETCHING FROM FIREBASE FINISH
    // THEN YOU WILL BE ABLE TO SEE THE RESULT
    print('${_userProfile.toString()}');

    _userProfile.forEach((key, value) => print('$key: $value'));

    return Container(
       child: Text(
          _userProfile.toString(),
       ),
    );
  }
}