如何从订阅返回 observable [英] How to return observable from subscribe

问题描述

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.

I'm trying to return an observable when I get a certain value in a subscriber, but I fail miserably.

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
        });
}

angular 2 中关于 observables 的资源并不多，所以我不知道从哪里开始.任何人都可以帮忙吗?

There are not many resources on observables in angular 2, so I don't know where to start. Can anyone help with this please?

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();
        }

推荐答案

你不能从 subscribe 返回一个 observable 但是如果你使用 map 而不是 subscribe 那么一个 Observable 会被返回.

You can't return an observable from subscribe but if you use map instead of subscribe then an Observable is returned.

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;
}

这篇关于如何从订阅返回 observable的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！