获取Observable返回的值 在Angular Typescript（Firebase）中

Question

因此，我有以下代码从Firebase用户列表中检索数据：

currentUserRef: AngularFireList<any>
currentUser: Observable<any>;

var user = firebase.auth().currentUser;

this.currentUserRef = this.af.list('usuarios', ref =>
ref.orderByChild('email').equalTo(user.email));
this.currentUser = this.currentUserRef.valueChanges();
this.currentUser.subscribe(res => console.log(res[0].condominio));

在检索到的数据中，我有两个属性：condominio和email。

在console.log（res [0] .condominio）上我有数据输出到控制台，但我需要将它保存到变量，例如：

userCond: string;

然后我必须从res获取属性'condominio'并将其设置为'userCond'，但如果我尝试这样做它不起作用：

this.currentUser.subscribe((res) => { this.userCond = res[0].condominio });

我究竟做错了什么？

"angularfire2": "^5.0.0-rc.11",
"firebase": "^5.3.1",
"ionic-angular": "3.9.2",

编辑：

    export class HomePage {

    currentUserRef: AngularFireList<any>
    currentUser: Observable<any>;

    moradorRef: AngularFireList<any>
    morador: Observable<any>;

   userCond: string;

   constructor(
    public authService: AuthService,
    public userService: UserService,
    public navCtrl: NavController,
    public navParams: NavParams,
    public af: AngularFireDatabase
   ) {

   }

   ionViewCanEnter(): Promise<boolean> {
     return this.authService.authenticated;
   }

   ionViewDidLoad(){
    debugger;
    //TRAZ AS MESMAS INFORMAÇÕES
    //this.userService.getCurrentUser();
    var user = firebase.auth().currentUser;

    //const _this = this;

    this.currentUserRef = this.af.list('usuarios', ref =>
    ref.orderByChild('email').equalTo(user.email));
    this.currentUser = this.currentUserRef.valueChanges();
    //this.currentUser.subscribe(res => 
    console.log(res[0].condominio));
    this.currentUser.subscribe(res => {
      debugger;
      this.userCond = res[0].condominio;
    });

    console.log(this.userCond);

Answer 1

  this.currentUser.subscribe(res => {
    this.userCond = res[0].condominio; // 'this' here refers to the observable, not the class instance
  });

要处理这个，请执行：

  const _this = this;
  this.currentUser.subscribe(res => {
    _this.userCond = res[0].condominio;
  });

Answer 2

将userCond定义为Observable。

userCond: Observable<string>;

之后，将condominio属性值映射到userCond，同时查询firestore。

this.currentUserRef = this.af.list('usuarios', ref =>
                              ref.orderByChild('email').equalTo(user.email));
this.userCond = this.currentUserRef.valueChanges()
                                       .pipe(map(res => res[0].condominio));

现在userCond可以订阅以获得价值，只要有需要。

Answer 3

问题是，您需要在使用类变量userCond之前等待订阅完成。订阅不是同步，只是您想要在订阅下使用的调用方法。

this.currentUser.subscribe(res => {
  this.userCond = res[0].condominio;
  this.loopOverAnotherList();
});

loopOverAnotherList() {
   // you can use this.userCond here
}