RxJS:我怎样才能做一个“如果"?与可观察对象? [英] RxJS: How can I do an "if" with Observables?

问题描述

假设我有两个 observable，一个我想监听一个 observable 的变化，如果另一个符合某个条件.我用 zip 尝试过，但似乎我只会收到通知，如果 两个 observables 都发生了变化，但是我希望在一个 observable 的每一个变化都收到通知，如果条件另一个是真的.

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，但我无法让它工作.

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

推荐答案

使用 可暂停:

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

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