我应该在 BehaviorSubject 中使用 asObservable 吗?

问题描述

我想知道 BehaviorSubject 中以下代码中的两种方法是什么.

I am wondering what is the two approach in the following code in BehaviorSubject.

据我所知:

asObservable 方法不仅将其转换为 Observable，还移除了 Observer 实现.因此你不能调用 next, error &在 asObservable() 返回的实例上完成.

但以下内容也让我感到困惑:

but the following also makes me confused:

通过仅公开 asObservable，您可以使用发出的值，但防止从创建此 BehaviorSubject 的服务外部更改 BehaviorSubject.为此，请使用 asObservable().

这些定义有什么问题吗?

Is there anything wrong with these definitions?

export class DataService {

    // usage I : using getter
    private messageSubject = new BehaviorSubject<any>(undefined);

    getMessage(): BehaviorSubject<any> {
        return this.messageSubject;
    }

    setMessage(param: any): void {
        this.messageSubject.next(param);
    }


    // usage II : using asObservable()
    private messageSubject = new BehaviorSubject<any>(undefined);

    currentMessage = this.messageSubject.asObservable();

    setMessage(param: any) {
    this.messageSubject.next(param)
    }
}

以上哪种方法更好用，或者这两种方法的优缺点是什么?

Which approach above is better to use or what is the pros and cons for these 2 approaches?

更新:上次我最终确定了正确的用法如下:

Update: Last time I finalised the correct usage as the following:

// usage III : using @martin's approach:
private messageSubject = new BehaviorSubject<any>(undefined);

public messages$: Observable<any> = this.messageSubject;

//should I set the observable still using the following method without any changing? Or do I need an update?
setMessage(param: any) {
    this.messageSubject.next(param)
}

推荐答案

实际上，在 TypeScript 中推荐的方法只是通过这样的类型转换:

Actually, the recommended way of doing this in TypeScript is only by type casting like this:

private messageSubject = new BehaviorSubject<any>(undefined);

public messages$: Observable<any> = this.messageSubject;

这样，TypeScript 编译器就不会让您调用 next()、error() 或 complete().仅在纯 JavaScript 中使用 RxJS 时才推荐使用 asObservable().例如，在 RxJS 源代码内部，它从不使用 asObservable() 即使它使用并暴露 Subjects =>大量观察.

This way it's TypeScript compiler who won't let you call next(), error() or complete(). Using asObservable() is recommened only when using RxJS in pure JavaScript. For example, internally in RxJS source code it never uses asObservable() even though it uses and exposes Subjects => Observables a lot.

更多信息见讨论:https://github.com/ReactiveX/rxjs/pull/2408

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