如何检查是否有人订阅了 Angular 中的 EventEmitter？

Question

有一个事件发射器：

@Output() edit: EventEmitter<any> = new EventEmitter();

如何检查是否有人订阅了 Angular 中的 EventEmitter？

Answer 1

AngularEventEmitter是一个 RXJS Subject：

class EventEmitter<T> extends Subject<T>

检查是否有订阅者/观察者

Subject.observed: bool-- 如果有 1 个或多个订阅者则为 true

RXJS 源代码

/**
 * A Subject is a special type of Observable that allows values to be
 * multicasted to many Observers. Subjects are like EventEmitters.
 *
 * Every Subject is an Observable and an Observer. You can subscribe to a
 * Subject, and you can call next to feed values as well as error and complete.
 */
export class Subject<T> extends Observable<T> implements SubscriptionLike {
  ...

  private currentObservers = new Map<number, Observer<T>>()

  get observed() {
    return this.currentObservers.size > 0;
  }

笔记

• 不要使用 an EventEmitter，而是考虑BehaviorSubjector ReplaySubject。

请参阅：委托：Angular 中的 EventEmitter 或 Observable