[Proposal] Pass default parameters into Screen Content() function

Hello, I'm trying to adopt your library into my pet project. I was faced with an issue, that the inner screen should consider padding from the parent screen.

Please take a look sample. I need to pass paddingValues into CurrentTab(). The Scaffold provides this value to prevent content overlapping.

TabNavigator(FlagsTab) { tabNavigator ->
            Scaffold(
                modifier = Modifier.systemBarsPadding(),
                topBar = {},
                content = { paddingValues ->
                    CurrentTab()
                },
                bottomBar = {
                    BottomNavigation {
                        TabNavigationItem(Tab1)
                        TabNavigationItem(Tab2)
                    }
                }
            )
        }

My suggestion is to make Screen interface like this with default parameters:

interface Screen : Serializable {

    val key: ScreenKey
        get() = this::class.qualifiedName
            ?: error("Default ScreenKey not found, please provide your own key")

    @Composable
    fun Content(
        modifier: Modifier = Modifier,
        paddingValues: PaddingValues = PaddingValues()
    )
}

Thanks a lot)

Hey guys, the voyager owner is very busy and his wife is pregnant. Updates will come soon. Stay up to date.

Nice! Just tried that but got the error Abstract Composable functions cannot have parameters with default values.

I'll try to find another way, suggestions are welcome.

Maybe you find a solution in the future - for now I just wanted to share my solution if someone else is looking here.

I simply solve that by using local compositions to provide custom data to sub composables and this looks like following for this use case:

// define a custom local composition
val LocalContentPadding = compositionLocalOf { mutableStateOf(PaddingValues()) }

fun MainScreen() {

  // rememeber the paddings here inside the root level
  val paddingValues = remember { mutableStateOf(PaddingValues()) }

  // provide the padding state  inside the local provider
  CompositionLocalProvider(
    LocalContentPadding provides paddingValuesTab
  ) {

    MyAppTheme {
      BottomSheetNavigator(
        sheetContent = {
          Navigator(NavScreenBottomSheet)
        },
        content = {
          TabNavigator(NavScreenTabHome) {
            Scaffold(
              topBar = {
                
              },
              content = { pv ->
                // update the paddings
                paddingValues.value = pv
                CurrentTab()
              },
              bottomBar = {
                
              }
            )
          }
        }
      )
    }
  }
}

And inside your tabs and/or sub screens you can now do following:

@Parcelize
object NavScreenTabHome : Screen, Parcelable {

  @Composable
  override fun Content() {
    val paddingValues = LocalContentPadding.current
    // use the padding in your composables...
  }
}

Create a new class ScreenX:

abstract class ScreenX: Screen {

    @Composable
    abstract fun Content(modifier: Modifier)

    @Composable
    final override fun Content() = Content(Modifier)
}

Inheriting from it the class of a specific screen:

object MainScreen : ScreenX() {
    @Composable
    override fun Content(modifier: Modifier) { 
       Column(modifier) {/* code */}
    }
}

create own CurrentScreen function with param:

@Composable
public fun CurrentScreen(modifier: Modifier) {
    val navigator = LocalNavigator.currentOrThrow
    val currentScreen = navigator.lastItem as ScreenX

    navigator.saveableState("currentScreen") {
        currentScreen.Content(modifier)
    }
}

and next in Scaffold:

Navigator(
        MainScreen
    ) {         
            Scaffold(content = {
                CurrentScreen(Modifier.padding(it))
            })
        }
)

We currently are using simpler solution

 Box(
    modifier = Modifier
        .padding(paddingValues)
        //.consumeWindowInsets(paddingValues), in case if you have internal scaffolds
) {
    CurrentTab()
}