在Angular 2中,有一些您不需要取消订阅的可观察对象.例如http requests和activatedRoute.params.
Angular/RxJs When should I unsubscribe from `Subscription`
但是当我使用switchMap时会发生什么情况,例如activatedRoute.params,并且在switchMap内部我访问一个服务,该服务返回一个observable,如果以通常的方式订阅则需要取消订阅.
像这样的东西:
this.activatedRoute.params .switchMap((params: Params) => this.userService.getUser(+params['id'])) .subscribe((user: User) => this.user = user);
如果我在没有switchMap且没有activateRoute.params的情况下调用this.userService,我将不得不取消订阅.
// userService.getUser() takes in optional id?: number. this.subscription = this.userService.getUser().subscribe( (user: User) => { this.user = user; } );
然后……
this.subscription.unsubscribe();
我的问题是,如果我在其上使用switchMap并调用需要取消订阅的服务,是否需要取消订阅activatedRoute.params?
解决方法
如果您订阅的源可观察对象总是完成或错误,则无需取消订阅.
但是,如果使用switchMap从源中组合另一个observable,是否需要取消订阅取决于switchMap中返回的observable.如果返回的observable并不总是完成或错误,那么,是的,您需要取消订阅.
如果源错误,将自动取消订阅:
const source = new Rx.Subject(); const composed = source.switchMap(() => Rx.Observable.interval(200)); composed.subscribe(value => console.log(value)); source.next(1); setTimeout(() => { console.log("Erroring..."); source.error(new Error("Boom!")); },1000);
.as-console-wrapper { max-height: 100% !important; top: 0; }
<script src="https://unpkg.com/rxjs@5.4.1/bundles/Rx.min.js"></script>
但是,如果源完成,则不会发生自动取消订阅:
const source = new Rx.Subject(); const composed = source.switchMap(() => Rx.Observable.interval(200)); composed.subscribe(value => console.log(value)); source.next(1); setTimeout(() => { console.log("Completing..."); source.complete(); },1000);
.as-console-wrapper { max-height: 100% !important; top: 0; }
<script src="https://unpkg.com/rxjs@5.4.1/bundles/Rx.min.js"></script>