如何获取RxJS Subject或Observable的当前值？ [英] How to get current value of RxJS Subject or Observable?

问题描述

我有一个Angular 2服务：

I have an Angular 2 service:

import {Storage} from './storage';
import {Injectable} from 'angular2/core';
import {Subject}    from 'rxjs/Subject';

@Injectable()
export class SessionStorage extends Storage {
  private _isLoggedInSource = new Subject<boolean>();
  isLoggedIn = this._isLoggedInSource.asObservable();
  constructor() {
    super('session');
  }
  setIsLoggedIn(value: boolean) {
    this.setItem('_isLoggedIn', value, () => {
      this._isLoggedInSource.next(value);
    });
  }
}

一切都很好。但我有另一个不需要订阅的组件，它只需要在某个时间点获取isLoggedIn的当前值。我该怎么做？

Everything works great. But I have another component which doesn't need to subscribe, it just needs to get the current value of isLoggedIn at a certain point in time. How can I do this?

推荐答案

A 主题或 Observable 没有当前值。当一个值被发出时，它被传递给订阅者并且 Observable 就完成了。

A Subject or Observable doesn't have a current value. When a value is emitted, it is passed to subscribers and the Observable is done with it.

如果你想要要获得当前值，请使用 BehaviorSubject ，这是为了这个目的而设计的。 BehaviorSubject 保留最后一次发出的值，并立即将其发送给新订阅者。

If you want to have a current value, use BehaviorSubject which is designed for exactly that purpose. BehaviorSubject keeps the last emitted value and emits it immediately to new subscribers.

它还有一个方法 getValue（）获取当前值。

It also has a method getValue() to get the current value.

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