Angular HTTP调用已订阅一个主题，从而关闭了该主题 [英] Angular HTTP call subscribed to a subject closing the subject

问题描述

我有两个可以获取给定对象的服务:初始HTTP调用以获取完整列表，以及websocket通知以实时更新新元素.

I have two services that can fetch a given object : an initial HTTP call to get the full list, and websocket notification to have live update of new elements.

我想将两个呼叫连接到相同的可观察对象，以便显示页面不了解后端.

I want to wire the two calls to the same observable so the display page has no knowledge of the backend.

有打电话的消息:

private getInitialData(subject: Subject<any>) {
    this._http.get<Array<any[]>>(`/call/to/backend`)
        .flatMap(items => items)
        .subscribe(subject);
}

private listenNewData(subject: Subject<any>) {
    this.websocketService.listen('/some/ws/topic')
        .subscribe(subject);
}

private initialize() {
    const subject = new Subject<any>();

    this.dataService.getInitialData(subject);
    this.listenNewData(subject);

    subject.subscribe(item => this.items.push(item))
}

以这种方式注册主题时，似乎该主题实际上是在HTTP解析后关闭的，并且没有websocket通知发送给该主题.

When registering this way the subject it seems the subject is actually closed after the HTTP resolution, and no websocket notification get sent to the subject.

但是，在订阅函数上使用回调注册时:

However, when registering using callbacks on subscribes functions :

private getInitialData(subject: Subject<any>) {
    this._http.get<Array<any[]>>(`/call/to/backend`)
        .flatMap(items => items)
        .subscribe(item => subject.next(item));
}

private listenNewData(subject: Subject<any>) {
    this.websocketService.listen('/some/ws/topic')
        .subscribe(item => subject.next(item));
}

我没有问题，所有物品都已正确提取.

I have no issues and all items are correctly fetched.

我想知道两个版本为何不同，为什么在第一种情况下，主题最终封闭.

I wanted to know why the two versions are different, and why, in the first case, the subject end up closed.

感谢您的帮助.

推荐答案

这是正确的行为.当您使用 .subscribe(subject)时，您将同时订阅所有三种类型的通知.所有主题都是观察者，因此与编写以下内容相同:

This is correct behavior. When you use .subscribe(subject) you're subscribing to all three types of notifications. All Subjects are observers so it's the same as writing the following:

.subscribe(
  v => subject.next(v),
  err => subject.error(err),
  () => subject.complete()
);

因此，如果仅使用 .subscribe(item => subject.next(item))，则仅传递 next 通知，而不会传递错误或 complete 通知，因此 subject 永远不会完成.

So if you use just .subscribe(item => subject.next(item)) you're passing only the next notifications and no error or complete notifications so subject is never completed.

这篇关于Angular HTTP调用已订阅一个主题，从而关闭了该主题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！