How do you handle progress bars when you're loading something from a Flow? Where do you set the prog...

# android

[Florian]

How do you handle progress bars when you're loading something from a Flow? Where do you set the progress bar to visible/gone?

For example:

private val activeChatsFlow = sessionManager.chatUserFlow.flatMapLatest { user ->
        repository.getActiveChatsForUser(user.uid!!)
   }

Are onStart and onCompletion the right combination?

[tseisel]

One solution is to make it part of the UI state exposed via `LiveData`/`Stateflow`. 2 approaches:
1. Use a sealed class with a Loading child having a progress property, for example
2. Add a loading: Boolean to your existing state.
You could then use onStart to update state with your loading flag, and clear it when active chats are available.

[Florian]

Thanks. Where do you set loading = false specifically?

[FunkyMuse]

Before you call the function that sets the flow alive
In this case before the repository.getActiveUserForChat and one after it's called

You can use onStart and onCompletion and it's gonna work too, which is the correct way to do so

[tseisel]

Given fun getActiveChatsForUser(user: User): List<Chat> and the given UI state class:

data class UiState(
  val loading: Boolean,
  val chats: List<Chat>
)

Then you would need to do the following:

chatUserFlow.flatMapLatest { user ->
  repository.getActiveChatsForCurrentUser(user.uid)
    .map { UiState(loading = false, chats = it) }
    .onStart { emit(UiState(loading = true, chats = emptyList()) }
}

[tseisel]

Progress indicator will be shown until chats are loaded for the first time, and will be shown again whenever chatUserFlow emits.

[FunkyMuse]

UI states should be sealed classes holding only one state at the moment

[Florian]

that's interesting, thank you

[Florian]

instead of map I could also use onEach to just set loading = false, right?

[Florian]

but onCompletion doesn't seem to work, it works the first time but not when I close and open the app again

[Colton Idle]

@Florian I've gone the rabbit hole of "UI states should be sealed classes" and it gets out of hand quickly and not really doable in things that aren't crazy simple. I think @Adam Powell talked me out of it? I just have state as a class and I can mix and match everything. Events on the other hand... those are sealed classes in my apps.

[Nathan Retta]

I have done both, modeling UI states as either a sealed class or a single data class. I generally prefer MVI with actions modeled as a sealed class and state as a data class. In cases like this, MVVM with a data class representing the UI state is a good compromise to avoid the overhead of a full MVI redux implementation

[Florian]

I think the discussion is derailing a bit

[Florian]

the original questions was where to set loading = true/false

[Michael Ferguson]

I follow a similar pattern to your example. I update my ui state loading in onStart and onCompletion in the flow returned to flatMapLatest. (That is, the “inner” flow.)

[Florian]

are you sure onCompletion is the right place to hide the progress bar? It is called when the Flow is closed

[Michael Ferguson]

That’s a fair point. I guess in my specific use case the inner flow does complete. I suppose if yours does not you’d have to move it into onEach .

[Florian]

thank you