Sample_of_rx_switch_map.kt

// Hold the disposable in order to cancel the operation later.
val sharingDisposable = mView
    .onClickStart()
    .switchMap { _ ->
        // 1. Generate BMP
        getGenBmpObservable()
            // 2. Show dialog
            .switchMap { _ -> 
                getDialogSingle().toObservable()
            }
            // 3. Share
            .switchMap { dialogPayload -> 
                if (dialogPayload.result == RESULT_OK) {
                    // If the user clicks OK, share to FB.
                    getShareToFacebookObservable(dialogPayload.data)
                } else {
                    // The EMPTY observable calls observer's onComplete()
                    // to indicate the stream is over.
                    Observable.empty()
                }
            }
    }
    .subscribe { _ ->
        Log.d("xyz", "all finished!")
    })

// When the cancel signal is received, dispose the observable chain.
onClickCancel()
    .subscribe { _ ->
        sharingDisposable.dispose()
    }