当 Rxjs 主题订阅/取消订阅时如何接收通知 [英] How can I receive notifications when Rxjs Subject is subscribed to / unsubscribed from

问题描述

我正在尝试使用 Rxjs 作为管理大型状态树中垃圾收集的一种方式.

I'm trying to use Rxjs as a way to manage garbage collection in a large state tree.

如何创建一个带有回调函数的操作符，该回调函数会在每次 observable 的订阅者数量改变时触发?

How can I create an operator that takes a callback function that is triggered every time the number of subscribers to the observable alters?

推荐答案

多种方式，都涉及隐藏你的主题并给消费者一个包装好的 observable:

Multiple ways, all involve hiding your subject and giving consumers a wrapped observable:

想知道什么时候订阅了你的主题?

Want to know when something subscribes to your subject?

const subject = new Subject();
const observable = Observable.defer(() => {
  someoneJustSubscribed();
  return subject;
});
return observable;

想知道何时有人退订?

const subject = new Subject();
const observable = subject.finally(() => someoneJustUnsubscribed());
return observable;

想知道两者吗?

const subject = new Subject();
const observable = Observable.create(observer => {
    someoneJustSubscribed();
    const sub = subject.subscribe(observer);
    return () => {
        someoneJustUnsubscribed();
        sub.unsubscribe();
    }
});
return observable;

这篇关于当 Rxjs 主题订阅/取消订阅时如何接收通知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！