Question

在服务中声明如下：

public currentDBUserBS$: any;

constructor(private afDb: AngularFireDatabase){}

fetchUser(uid){
  this.afDb.object(`users/${uid}`).valueChanges().subscribe((dUser) => {
    if (dUser) {
      this.currentDBUserBS$ = dUser;
    }
  });
}

现在尝试在模板中使用

template: `<li *ngIf="(authService.currentDBUserBS$ | async)?.role=='admin'"> Something </li>`

错误堆栈：

ERROR Error: InvalidPipeArgument: '[object Object]' for pipe 'AsyncPipe'
    at invalidPipeArgumentError (common.js:4219)
    at AsyncPipe._selectStrategy (common.js:5630)
    at AsyncPipe._subscribe (common.js:5612)
    at AsyncPipe.transform (common.js:5586)
    at Object.View_AppNavigatorComponent_0._co [as updateDirectives] (AppNavigatorComponent.html:40)
    at Object.debugUpdateDirectives [as updateDirectives] (core.js:14339)
    at checkAndUpdateView (core.js:13508)
    at callViewAction (core.js:13858)
    at execComponentViewsAction (core.js:13790)
    at checkAndUpdateView (core.js:13514)

Answer 1

您正在从Firebase获取currentDBUserBS$对象，而不是Observable。如果您想这样做，则必须删除模板中的| async。

但是，您可以执行以下操作：

fetchUser(uid){
  this.currentDBUserBS$ = this.afDb.object(`users/${uid}`).valueChanges();
}

.valueChanges()为您提供了一个可观察的，并会在发出新值或修改现有值时自动更新。

Answer 2

您必须在订阅操作后添加.valueChanges();。它是必需的，如下所示：

 this.courses$=db.list('/courses').valueChanges();

管道'AsyncPipe'的InvalidPipeArgument：'[object Object]'

2 个答案: