无需订阅即可从Observable获取当前值(只需一次获得所需值) [英] Get current value from Observable without subscribing (just want value one time)

问题描述

标题说明了一切.如何在不订阅的情况下从Observable获取当前值?我只希望当前值一次而不是新值，因为它们会传入...

The title says it all really. 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相似，只不过它只记住最后一个发布.
• BehaviorSubject还要求您提供默认值T.这意味着所有订阅者都将立即收到一个值. (除非它已经完成).

• BehaviorSubject is similar to ReplaySubject except it only remembers the last publication.
• BehaviorSubject also requires you to provide it a default value of T. This means that all subscribers will receive a value immediately (unless it is already completed).

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提供一个名为value的getter属性，以获取通过它的最新值.

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

StackBlitz

• 在此示例中，将值"a"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

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隐藏主题并仅公开其值

如果您想隐藏BehaviorSubject并仅公开其值(例如，从Service进行访问)，则可以使用这样的getter.

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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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