I've this code in a `ViewModel`: ```private val testSingle = Single.just("item1") private val foo =...

# android

[iex]

I've this code in a `ViewModel`:

private val testSingle = Single.just("item1")

private val foo = testPublishSubject.startWith(testSingle.toObservable().doOnNext {
    Timber.i(">>> single on next: $it")
}).doOnNext {
    Timber.i(">>> PS on next: $it")
}

fun onSomeEvent() {
    testPublishSubject.onNext("item2")
}

So it's a PublishSubject that gets initialized with a Single . On certain event, I push a new value to the subject. So far so good!
The problem: I navigate to next screen and navigate back. Then the subject is reset to the initial Single value ("item1"). Why? The ViewModel is not reinitialized.

[stantronic]

is the viewmodel in an activity or fragment?

[Hitender Pannu]

Could you confirm again the lifecycle of the viewModel by logs inside init.

[iex]

actually, the reason is that the fragment subscribes to foo again. (It's in a fragment and it subscribes in onCreateView )

[iex]

But my use case is a bit more complex; The Single is fetching data from preferences, and it doesn't re-fetch it when going back for some reason.

[iex]

okay I guess this is because the Single 's result is cached... 🤔

[iex]

so how do I fix this? I want that Single is executed again

[stantronic]

yeah, the question is why the other value wasnt cached

[stantronic]

turn it from a val to a fun

[iex]

because the fragment disposes the subscription and subscribes again

[stantronic]

that should do it

[iex]

probably yeah

[iex]

trying it out

[iex]

yeah it fixes it. Thanks @stantronic!

[iex]

I want to understand it too though 😛

[iex]

the code actually looks more like this:

private val foo = testPublishSubject.startWith(myRepo.mySingleCall().toObservable())

[iex]

Why is it basically reinitializing the PublishSubject but not calling the Single again?

[iex]

I'd expect that this is called myRepo.mySingleCall() when reinitializing the subject

[stantronic]

what does the mySingleCall() function look like - it sounds like something has been cached at that level

[iex]

not really...

fun selectedModel(): Single<Optional<Model>> =
    (preferences.getString(SELECTED_MODEL)?.let {
        Some(Model(it))
    } ?: None).let{ Single.just(it) }

[iex]

it just accesses preferences

[stantronic]

hmm. strange

[iex]

that code can actually be simplified to fun selectedModel() = Single.just("foo")

[stantronic]

if that was the one that was a “val” earlier, then it would capture the value at that point. You could rewrite as

Single.fromCallable { /* fetch from preferences here */  }

[stantronic]

and that should also fetch each time.

[iex]

but it's not a val. I posted this snippet above:

private val foo = testPublishSubject.startWith(myRepo.mySingleCall().toObservable())

[iex]

I mean the Single is not a val

[iex]

where mySingleCall() is implemented basically like this: fun mySingleCall() = Single.just("foo")

[iex]

(it fetches from preferences instead but it comes down to the same)