RxJS：我怎么能做“if”与Observables？ [英] RxJS: How can I do an "if" with Observables?

问题描述

假设我有两个observable和一个我想听一个observable的变化，如果另一个匹配某个条件。我尝试使用 zip ，但似乎我只会收到通知，如果两个 observables都发生了变化，但我希望在每次更改时收到通知一个可观察的，如果另一个的条件是真的。

Say I have two observables and one I want to listen on changes in one observable, if the other on matches a certain condition. I tried it with zip but it seems I will only be notified, if both observables change, but I want to be notified for every change on the one observable, if the condition of the other one is true.

我尝试了什么：

var firstState = new Rx.BehaviorSubject(undefined);
var secondState = new Rx.BehaviorSubject(undefined);

Rx.Observable.zip(firstState, secondState, function (first, second) {
  return {
    first: first,
    second: second
  }
}).filter(function (value) {
  return value.first !== undefined;
}).subscribe(function (value) {
  // do something with value.second
}); 

我注意到有一个 Rx.Observable.if ，但我无法工作。

I noticed there is an Rx.Observable.if, but I couldn't got it to work.

推荐答案

使用 pausable ：

secondState
    .pausable(firstState.map(function (s) { return s !== undefined; }))
    .subscribe(function (second) {
        // only occurs when first is truthy
    });

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