我应该在Angular中使用switchMap，flatMap还是任何其他rxjs运算符

Question

I have two streams of data, second one depends on first one, but i want to be able to catch a change of second one. I wrote 2 functions for creating observables. I am wondering if this implementation is correct.

firstObservable(){
  ...
};
secondObservable(someValue){
  ...
}
let subscription = firstObservable().switchMap(r => {
  if (r.someValue){
    return secondObservable(r.someValue);
  }else{
    return Observable.empty();
  }
}).subscribe( ... );

Answer 1

If you could be more specific about what you are asking it would help but from what I understand it looks fine.

I think that you probably want to use switchMap instead of flatMap. FlatMap will maintain multiple inner subscriptions while SwitchMap will only maintain a subscription to the latest inner observable. So if you want to only get values from the inner observable based on the output of the source then switchMap will do that.

Not sure of your use cases but you might want to consider applying a filter instead of returning Observable.empty().

Here is an example:

 const firstObservable = Rx.Observable.create((o) => { o.next(); setTimeout(() => o.next(1), 1000); setTimeout(() => o.next(), 2000); setTimeout(() => o.next(2), 3000); setTimeout(() => o.complete(), 4000); }).do(console.log.bind(null, 'first: next'), console.log.bind(null, 'first: error'), console.log.bind(null, 'first: complete')); const secondObservable = (x) => Rx.Observable.interval(x * 500).take(5) .do(console.log.bind(null, 'second: next'), console.log.bind(null, 'second: error'), console.log.bind(null, 'second: complete')); firstObservable.filter(x => x).switchMap(x => secondObservable(x)) .subscribe(console.log.bind(null, 'stream: next'), console.log.bind(null, 'stream: error'), console.log.bind(null, 'stream: complete')); 

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