为什么要使用RxJS .asObservable()getter/factory函数模式?

问题描述

在许多使用RxJS的代码库中，我似乎遇到了通过 getter 或普通 getObservable()函数.我的问题不是为什么使用 .asObservable()，而是为什么它看起来如此普遍地封装在getter/factory函数中?

In a lot of codebases using RxJS I seem to come across the pattern of exposing private Subjects as Observables via a getter or normal getObservable() function. My question is not why .asObservable() is used, but instead why it seems so commonly wrapped in a getter/factory function?

封装在getter/factory函数中的asObservable()

private readonly _engineInfo$ = new Subject<EngineInfo>();
get engineInfo$() { return this._engineInfo$.asObservable(); }

asObservable()作为实例变量

private readonly _engineInfo$ = new Subject<EngineInfo>();
public engineInfo$ = this._engineInfo$.asObservable();

问题

• 我不了解的是，每次订阅 Subject 时， .asObservable()都会创建一个新的 Observable .创建的 Observable 也是 hot ，可以多次订阅.为什么要创建多个 Observable ，(每个访问/订阅一个)的匿名实例，而不是只创建一个 Observable ，所有观察员都订阅了一项/一项服务吗?
• 此 getter/factory function 模式是否有明显优势?
• 可能是由于垃圾收集或测试/模拟的优势吗?

• My undestanding is that .asObservable() creates a new Observable every time that subscribes to the Subject. Also the created Observable is hot and can be subscribed multiple times. Why would one create multiple anonymous instances of Observable, (one for each access/subscription), instead of having just one Observable, accessed at one class/service, that all observers subscribe to?
• Is there a non-obvious advantage to this getter/factory function pattern?
• Could it be because of garbage collection or testing/mocking advantages?

到目前为止，我在所有服务/类中都使用了第二个示例中的实例变量设置，并且一切似乎都可以正常工作，并且具有多个观察者.

So far I'm using the instance variable setup from the second example in all services/classes and everything seems to works as expected, also with multiple observers.

推荐答案

何时使用Subject.prototype.asObservable()

此操作的目的是防止对象的观察者侧"泄漏出API.基本上是为了防止在您不希望人们能够接着"到结果可观察对象中时进行抽象泄漏.

When to use Subject.prototype.asObservable()

The purpose of this is to prevent leaking the "observer side" of the Subject out of an API. Basically to prevent a leaky abstraction when you don't want people to be able to "next" into the resulting observable.

您永远不想将Subject实例返回到调用上下文.这样做有点类似于返回Deferred对象而不是Promise.并且，这会使主体对意料之外的破坏性使用持开放态度.这样，在公开主题时，您可能需要先将其转换为可观察对象.

You never want to return a Subject instance to the calling context. Doing so would be somewhat akin to returning a Deferred object rather than a promise; and, it would leave the Subject open to unanticipated and corrupting usage. As such, when exposing a Subject, you'll probably want to convert it to an Observable first.

要执行此操作，我们可以使用 Rx.Observable.prototype.asObservable()实例方法.

To get this working we can use the Rx.Observable.prototype.asObservable()instance method.

主题本身是热/可共享的，它充当源Observable和许多观察者之间的桥梁/代理人，使多个观察者可以共享相同的Observable执行.

The subject itself is hot/sharable and it acts as a bridge/proxy between the source Observable and many observers, making it possible for multiple observers to share the same Observable execution.

此吸气剂/工厂功能模式是否有明显优势?
不会，一点也不，因为您正在创建一个新的以该Subject为源的Observable，以将其隐藏在使用Observable的代码中.

Is there a non-obvious advantage to this getter/factory function pattern?
Nope, not at all since you are Creating a new Observable with this Subject as the source to conceal it from code that uses the Observable.

何时在rxjs中使用asObservable()?

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