如何从订阅中返回 observable

Question

当我在订阅者中获得某个值时，我试图返回一个 observable，但我失败了。

这是代码：

 canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // get route to be activated
    this.routeToActivate = route.routeConfig.path;

    // get user access levels
    return this._firebase.isUserAdmin          <-- returns Subscription, not Observable
        .map(user => user.access_level)
        .subscribe( access => {
           // I need to return an observable here
        });
}

角度 2 中的 observables 资源并不多，所以我不知道从哪里开始。有人可以帮忙吗？

更新 - >工作版本

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
            // get route to be activated
            this.routeToActivate = route.routeConfig.path;

            // get user access levels
            return this._firebase.isUserAdmin
                .map(user => {
                    let accessLevel = user.access_level;

                    if (accessLevel === 'admin' ) {
                        return true;
                    }

                }).first();
        }

原文由 Dragos Ionescu 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

您不能从 subscribe 返回 observable，但如果您使用 map 而不是 subscribe Observable 。

 canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // get route to be activated
    this.routeToActivate = route.routeConfig.path;

    // get user access levels
    return this._firebase.isUserAdminObservable
        .map(user => {
           // do something here
           // user.access_level;
           return true;
         })
        .first(); // for the observable to complete on the first event (usually required for `canActivate`)
        // first needs to be imported like `map`, ...
}

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // get route to be activated
    this.routeToActivate = route.routeConfig.path;

    let subject = new Subject();
    // get user access levels
    this._firebase.isUserAdminObservable
        .map(user => {
          let accessLevel = user.access_level;
          if (accessLevel === 'admin' ) {
            subject.emit(true);
            subject.complete();
          }
          return user;
        });
     return subject;
}

原文由 Günter Zöchbauer 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

如果您想订阅 observable，请执行此操作，处理结果，然后在订阅中返回相同的结果：

 function xyx(): Observable<any> {
    const response = someFunctionThatReturnsObservable().pipe(map(result => {
          // here do any processing of the result //
          return result; // return back same result.
       }
    ))
   return response;
}

原文由 Zaslam 发布，翻译遵循 CC BY-SA 4.0 许可协议