无需订阅即可从 Observable 获取当前值(只需要一次值) [英] Get current value from Observable without subscribing (just want value one time)

问题描述

如何在不订阅的情况下从 Observable 中获取当前值?我只想要一次当前值，而不是它们进来时的新值.

How can I get the current value from an Observable without subscribing to it? I just want the current value one time and not new values as they are coming in.

推荐答案

您需要使用 BehaviorSubject,

• BehaviorSubject 与 ReplaySubject 类似，只是它只记住最后一次发布.
• BehaviorSubject 还要求您为其提供默认值 T.这意味着所有订阅者都会立即收到一个值(除非已经完成).

它将为您提供 Observable 发布的最新值.

It will give you the most recent value published by the Observable.

BehaviorSubject 提供了一个名为 value 的 getter 属性来获取通过它传递的最新值.

BehaviorSubject provides a getter property named value to get the most recent value passed through it.

StackBlitz

• 在此示例中，值a"被写入控制台:

//Declare a Subject, you'll need to provide a default value.
const subject: BehaviorSubject<string> = new BehaviorSubject("a");

用法:

console.log(subject.value); // will print the current value

<小时>

隐藏主题，只暴露它的价值

如果你想隐藏你的 BehaviorSubject 并且只公开它的值，比如说从 Service 中，你可以使用这样的 getter.

---

Conceal the Subject and only expose it's value

In case you want to conceal your BehaviorSubject and only expose it's value, let's say from a Service, you can use a getter like this.

export class YourService {
  private subject = new BehaviorSubject('random');

  public get subjectValue() {
    return this.subject.value;
  }
}

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