Get list from Single<List> observable

Question

I have a method which returns Single<List<HistoryItem>>. Now I want to get list from this.

private fun getListOfDownload(): ArrayList<HistoryItem> {
    val downloads = manager.lastHundredVisitedHistoryItems()
    downloads.subscribe { t ->
        return t; // not allowed
    }
}

I could use subscribe but that does not allow me to return list from that.

I tried map also.

downloads.map { t: List<HistoryItem> -> return t } // again `return t` is not allowed.

Edit

I could make this work by following

private fun getListOfDownload(): ArrayList<HistoryItem> {
        var list = ArrayList<HistoryItem>()
        val downloads = manager.lastHundredVisitedHistoryItems()
        downloads.subscribe { t ->
            list = t as ArrayList<HistoryItem>
        }
        return list
    }

Please tell

• If this way is right & will it not block main thread?
• Is there not a way to return the list without declaring another list?

I am new to Reactive programming so please explain me.

Answer 1

In your code getListOfDownload is returning the ArrayList<HistoryItem>, while lastHundredVisitedHistoryItems of manager returning Single<ArrayList<HistoryItem>> which means the you want to observe ArrayList<HistoryItem>, becuase lastHundredVisitedHistoryItems gonna take some times.

that's why you can not return the item in subscribe block because that block is lamda which is going to observe ArrayList<HistoryItem> item.

But if you don't care about the observation you can do something like this,

private fun getListOfDownload(): ArrayList<HistoryItem> {
    val downloads = manager.lastHundredVisitedHistoryItems()
    return downloads.blockingGet()
}

But you are loosing the asynchronus call of lastHundredVisitedHistoryItems as we are applying blockingGet(), but as you are not observing it on seperate thread i am assuming that you want to call it on main thread.

But if you want to observe lastHundredVisitedHistoryItems() then you can pass the method as a parameter which will act as cosumer for ArrayList<HistoryItem>.

private fun getListOfDownload( listener : (ArrayList<LoginViewModel.HistoryItem>) -> Unit) {
        val downloads = manager.lastHundredVisitedHistoryItems()
        downloads.subscribe { t -> listener.invoke(t) }
}

// when you call above method look like below
// here variable `it` is nothing but a object of ArrayList<LoginViewModel.HistoryItem>
getListOfDownload { adapter.updateDataSet(it) }