在Firebase的角度8中显示displayName

我在显示我的“displayName”属性时遇到问题组件.ts文件(用于控制台.log),但它在模板中运行良好。

 constructor(
    private fb: FormBuilder,
    private auth: AuthService
  ) { }
  ngOnInit() {
    this.buildForm();
    console.log(this.auth.user.displayName); // this line is the problem
  }

但是,这在模板中运行良好:

{{ user.displayName }}

如果你需要更多的服务细节。。。

验证服务.ts

export class AuthService {

  user: Observable<User>;

  constructor(
    private afAuth: AngularFireAuth,
    private afs: AngularFirestore,
  ) {
    //// Get auth data, then get firestore user document || null
    this.user = this.afAuth.authState.pipe(
      switchMap(user => {
        if (user) {
          return this.afs.doc<User>(`users/${user.uid}`).valueChanges();
        } else {
          return of(null);
        }
      })
    );
  }