Using RxJava autoConnect() and Relay to host a stream in a ViewModel

We may restore the view state in some way (e.g. with savedInstanceState), but then on rotations we would create another network request (and cancel any network request if active).

Hosting the stream in a lifecycle.ViewModel, we can have a stream lifecycle decoupled from the Activity’s. Using .autoConnect() we define the Observable to connect upstream (to the endpoint in this example) when the first Activity subscribes. When the activity disposes the connection, the upstream is kept alive. When the ViewModel itself is disposed (in onCleared) we dispose the upstream:

class MyViewModel(
    val endpoint: Endpoint
) : ViewModel() {    private val disposables = CompositeDisposable()    val viewState: Observable<Data> =
        endpoint
            .getData()            // Replay the last emitted value to new subscribers.
.replay(1)            // A single upstream connection is made on 
            // the first subscription and shared with 
            // all future subscribers.
            .autoConnect(1) { 
// Upstream disposable kept for later disposal.
                disposables.add(it) 
            }    override fun onCleared() {
        disposables.dispose()
        super.onCleared()
    }
}