如何使用RxSwift将两个observable合并到另一个observable？

Question

How to merge two observable to another observable with RxSwift? In my case:

struct ViewModel {

let items: Observable<[MediaAsset]>

init(type: Observable<AssetMediaType>, provider: DataProvider) {
    items = Observable.combineLatest(type, provider.rx.didAuthorize, resultSelector: { (type, status)  in
        return provider.rx.fetchMedia(type)
    })
}

public var didAuthorize: Observable<AuthorizeResult> {
    return Observable.create { o in
       //....
    }
}

public func fetchMedia(_ withType: AssetMediaType) -> Observable<[MediaAsset]> {
    return Observable.create { observer in
       //....
    }
}

but xcode build failed for reason:

Cannot convert value of type '(AssetMediaType, ) -> Observable<[MediaAsset]>' to expected argument type '( , _) -> _'

Answer 1

If you want them to fire at the same time you need to use a Zip

let zipped = Observalbe.zip(a, b){$0}

or in your code

struct ViewModel {

let items: Observable<[MediaAsset]>

init(type: Observable<AssetMediaType>, provider: DataProvider) {
    items = Observable.zip(type, provider.rx.didAuthorize){$0}

}

Answer 2

Root Issue:

Your types are mismatched.

Assuming that those functions belong to DataProvider.rx, instead of ViewModel, This code:

Observable.combineLatest(type, provider.rx.didAuthorize, resultSelector: { (type, status)  in
    return provider.rx.fetchMedia(type)
})

returns an Observable< Observable<[ViewModel.MediaAsset]>>

but you declared items as an Observable<[MediaAsset]>

Solution: Flatten the observable

items = Observable.combineLatest(type, provider.didAuthorize) { type,status in
        return (type,status)
    }
    .flatMapLatest { type,status in
        return provider.fetchMedia(type)

    }

Note: It's unclear how you are using status. I passed it to the flatMapLatest, but it won't be passed along any further.