[Question] Navigation change and life cycle edge case

[Ethan1983]

I'm running into an edge case and wanted to pick your brain on this, here is the use case

UI Event triggers a slow network op which starts with a loading state
UI is updated with a progress indicator
User backgrounds the app
Network op finishes while the app is in background (assume no process kill by android)
UI is subscribed to changes until onDestroy and gets notified of a navigation effect
Navigation Effect tries to perform fragment transaction while the app is paused
Things go haywire from here.

One approach to solve this was by having UI subscribe only until onPause and resubscribe from onResume. However, with this the effect notification is lost (no active subscriptions from paused state) when slow network op finishes while the app is backgrounded and re-subscription onResume fails as effect has no replay behavior from the view model.

This is kind of forcing navigation changes into view state. How do you go about this?

[Ethan1983]

Not to mention, canceling the task onPause and restart onResume is a no go.

[ScottCooper92]

How are you subscribing/observing the navigation effects? I've just tested your scenario and although the LiveData is updated, the Observer isn't triggered until the app is resumed again, meaning no navigation events when the app is backgrounded.

[Ethan1983]

In my case, it is scoped to pause and resume. However re-subscribing from onResume is no good as the effect observable has no cache/replay behavior (in the case where task finishes while the app is backgrounded).

If you are using LiveData, it might work as it has a cache but it would break config change use cases where the same effect would be notified again to the new fragment/activity instance.

@kaushikgopal Any thoughts?

[jhowens89]

I was just poking around the Roxie github page so forgive me if I'm way off on what you're trying to accomplish, but would this suit your purpose?

https://github.com/akarnokd/RxJavaExtensions/blob/master/src/main/java/hu/akarnokd/rxjava2/subjects/DispatchWorkSubject.java

While I don't use Roxie, I do use RxRedux and I use a subscription held in my ViewModel to a DispatchWorkSubject for queueing up "navigation" in the form of view animations in onStart.

I've also been wanting to dig more into LifecycleCoroutineScope. I've found some great uses for it, but I haven't done enough investigation to know if it can be a solution to this particular problem too.

[Ethan1983]

I was just poking around the Roxie github page so forgive me if I'm way off on what you're trying to accomplish, but would this suit your purpose?

https://github.com/akarnokd/RxJavaExtensions/blob/master/src/main/java/hu/akarnokd/rxjava2/subjects/DispatchWorkSubject.java

While I don't use Roxie, I do use RxRedux and I use a subscription held in my ViewModel to a DispatchWorkSubject for queueing up "navigation" in the form of view animations in onStart.

I've also been wanting to dig more into LifecycleCoroutineScope. I've found some great uses for it, but I haven't done enough investigation to know if it can be a solution to this particular problem too.

@jhowens89 Thx, do you have a working sample code handling both foregrounded and backgrounded state. I'm interested in how your subscription to DispatchWorkSubject is setup to handle both cases?