有条件地选择RxJS中的observable [英] Conditionally choose observable in RxJS

问题描述

我想知道如何创建一个新的observable，它将返回两个其他observable中的一个，基于第一个observable是否为空（默认情况下不调用第二个observable）。例如：

I would like to know how to create a new observable that will return one of two other observables based on if the first observable is empty (without calling the second observable by default). Eg:

// scenario 1
let obs1 = Observable.empty();
let obs2 = Observable.of([1,2,3]);
// This line doesn't work, but is essentially what I'm attempting to do
let obs3 = (obs1.isEmpty()) ? obs2 : obs1;
obs3.subscribe( i => console.log('Next: ', i));
// Next: 1
// Next: 2
// Next: 3
// Complete

// scenario 2
let obs1 = Observable.of([6,7,8]);
let obs2 = Observable.of([1,2,3]);
// This line doesn't work, but is essentially what I'm attempting to do
let obs3 = (obs1.isEmpty()) ? obs2 : obs1;
obs3.subscribe( i => console.log('Next: ', i));
// Next: 6
// Next: 7
// Next: 8
// Complete

推荐答案

你可以试试：

let obs3 = obs1.isEmpty().map(x => x? obs2 : obs1;)

现在快速检查一下是否有效。

Will check quickly now if that would work.

是的，根据 doc ，应该没问题， as isEmpty 发出一个布尔值，如果observable为空，则为true，因此你可以用它来获取你想要的observable。

Yep, according to the doc, it should be fine, as isEmpty emits a boolean which is true if the observable is empty, so you can use that to pick up the observable you want.

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