Decompose out multiple circuit internals for reuse + publicize CircuitContent

[ZacSweers]

This allows more granular use of CircuitContent and bringing your own presenter/ui instances. This allows more advanced presenters that could choose to pass composable lambdas in as state properties with tight linking of shared state.

It's a little verbose right now as I'm not sure what the best spots are to offer default values or not, but I think that's ok since these are advanced use cases and we can get feedback now. It doesn't take a particularly strong opinion on how to do this, just opens up doors.

// A state with nested content controlled by the presenter.
// Alternatively, the state could expose a presenter factory for the nested content too
data class MyState(
  // other props
  val nestedContent: @Composable () -> Unit,
)

// In a presenter with an injected anotherPresenterFactory and circuit instance
@Composable
override fun present(): MyState {
  val sharedState = remember { mutableStateOf("") }   

  val nestedPresenter = rememberPresenter(...) {
    anotherPresenterFactory.create(sharedState)
  }

  return MyState(...) {
    CircuitContent(NestedScreen, nestedPresenter, ui = rememberUi(screen, ..., circuit::ui))
  }
}

// The UI slots it in
@Composable fun MyUi(state: MyState, modifier: Modifier) {
  Scaffold(modifier) {
    state.nestedContent()
  }
}

[ZacSweers]

CCing some possibly interested parties @bryanstern @chrisbanes

[bryanstern]

I like this and definitely have a use case for it.

[chrisbanes]

I like the idea behind it! I've been using similar with Decompose in a work project, and being able to treat the UI as a big tree has some nice advantages (but downsides too).

I'm not sure on the example listed in the PR though. Feels a bit... messy to me, leaking the layers of presenter, state and UI into each other.

Personally I think only the nested presenter should be in the state, and then the 'parent UI' should be responsible for the rest of it. WDYT?

[ZacSweers]

that's very fair, the example here was more or less tossed together quick and based on some DMs between Bryan and I. For the last bit, do you mean just making the presenter instance a property in the state?

[chrisbanes]

Yeah exactly. It's similar to what Decompose does.