Rx.Subject丢失事件 [英] Rx.Subject loses events

问题描述

有人可以解释这三种变体之间的差异吗？

Can anybody explain what the differents between these 3 variants?

http://jsfiddle.net/8vx2g3fr/2/

1. 首先作为感谢，所有事件都是处理。


2. 但第二次输掉上一次比赛（3）


3. 第三次输掉第二项赛事（2）

您能帮助我了解问题所在以及如何使第三个变体处理所有事件吗？

Could you please help me to understand what the issue is and how to make the third variant process all events?

let bs = new Rx.Subject();
bs
    .subscribe(v=>{
        console.log("in", v);
        if (v % 2 == 0) {
            setTimeout(()=>{
                console.log(" out", v, "->" , v + 1);
                bs.next(v+1);
            }, 0);
        }
    });

bs.next(0);
bs.next(2);

输出：

in 0
in 2
 out 0 -> 1
in 1
 out 2 -> 3
in 3

2

2

let bs2 = new Rx.Subject();
bs2
    .subscribe(v=>{
        console.log("in", v);
        if (v % 2 == 0) {            
            Rx.Observable.interval(0).take(1)
                .map(()=>{console.log(" out", v, "->" , v + 1);return v+1;})
                .subscribe(bs2);
        }
    });

bs2.next(0);
bs2.next(2);

输出：

in 0
in 2
 out 0 -> 1
in 1
 out 2 -> 3

3

3

let bs3 = new Rx.Subject();
bs3
    .switchMap(v=>{
        console.log("in", v);
        if (v % 2 == 0) {            
            return Rx.Observable.interval(0).take(1)
                .map(()=>{console.log(" out", v, "->" , v + 1);return v+1;});
        }

    return Rx.Observable.empty();     
    }).subscribe(bs3);

bs3.next(0);
bs3.next(2);

输出：

in 0
in 2
 out 2 -> 3
in 3

推荐答案

这一切都在事实上预期的行为。

This all is in fact expected behavior.

令人困惑的是当您重复使用 Subject 和运营商如<$ c时会发生什么$ c> take（）多次。

The confusing thing is what happens when you reuse Subjectand an operator such as take() multiple times.

运营商 take（1）需要只需一个值并发送完成通知。由于 .subscribe（bs2），主题会收到此通知。现在是最重要的部分。

当主题收到完成或错误通知它标记为已停止。这意味着永远不会汇出任何项目或通知，这是Rx中的正确和预期行为。通知完成或错误必须是最后一次排放。

Operator take(1) takes just a single value and send complete notification. This notification is received by the Subject because of .subscribe(bs2). Now comes the most important part.
When a Subject receives a complete or error notification it marks itself as stopped. This means it will never remit any items or notifications which is correct and expected behavior in Rx. Notifications complete or error have to be the last emissions.

所以主题由第一个 take（1）完成，由值 0 （ bs2.next（0）致电）。

So the Subject is completed by the first take(1) which is triggered by value 0 (the bs2.next(0) call).

然后当值 2 触发 Observable.interval（0）.take（1）的第二次运行主题但它会被自动忽略，因为主题已标记为已停止。

Then when value 2 triggers the second run of the Observable.interval(0).take(1) it's received by the Subject but it's automatically ignored because the Subject is already marked as stopped.

第三个演示中的过程完全相同。

The process in you third demo is exactly the same.

您可以在 Subject.ts的源代码中看到它：

• https://github.com/ReactiveX/rxjs/blob/master/src/Subject.ts#L86

h ttps：//github.com/ReactiveX/rxjs/blob/master/src/Subject.ts#L56

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