Observable subscribe alway once issue

debugcn Published at Dev

Karim

I writing async unit tests for RxSwift,this my code,I can't understand subscribe only once

class TestViewModel: NSObject {
    let result : Observable<Int>

     init(input:Observable<Int>) {
        result = input.flatMapLatest({ (value) -> Observable<Int> in

            return Observable.create({ (observer) -> Disposable in

                DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 1, execute: {
                print("next"+"  \(value)")
                    observer.onNext(value)
                })

                return Disposables.create()
            })
        })
    }

}

    func testCount() {
        let expectation = XCTestExpectation(description: "async")
        let input = scheduler.createHotObservable([.next(100, 1),.next(200, 10)])
        let viewModel = TestViewModel.init(input: input.asObservable())
        viewModel.result.subscribe(onNext: { (value) in
            print("subscribe"+"   \(value)")
        }).disposed(by: disposeBag)
        scheduler.start()
        wait(for: [expectation], timeout: timeout)
    }

print info:

next  1
next  10
subscribe   10

I think print info should :

next  1
next  10
subscribe   1  
subscribe   10

Someone can give me suggestion？thank

Maxim Kosov

It's how flatMapLatest operator works. Its basically tells "map events into observables but use only recent observable's result". So, you map your events into two observables:

1: --1sec-> 1

10: --1sec-> 10

Most recent observable at the moment is for 10.

Try to use flatMap instead of flatMapLatest.

You should also avoid Observable.create if possible. In your particular case (to delay a value) you could use Observable.timer or Observable.just(...).delay(...).

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