Is there a way to detect preview mode?

# compose

[salomonbrys]

Is there a way to detect preview mode?

[pavi2410]

I don't think so, but you could do something like this

val PreviewAmbient = ambientOf { false }

@Preview
@Composable
fun MainScreenPreview() {
  Providers(PreviewAmbient provides true) {
    MainScreen()
  }
}

@Composable
fun MainScreen() {
  val isInPreview = PreviewAmbient.current
  ...
}

[salomonbrys]

That's what I currently do... But if I forget to provide the ambient in a preview, then I get "ViewModels creation is not supported in Preview" errors. So I'm looking for a more resilient way.

[salomonbrys]

How about

@Composable val isPreview: Boolean get() = ContextAmbient.current.applicationContext !is Application

?

[Joost Klitsie]

I think the common way is to write your composables as to not have them rely on a system. So instead of:

@Preview
@Composable
fun MainScreen() {
    val viewModel by viewModels()// or however kids these days get their viewmodel
}

@Composable
fun MainScreen() {
    val viewModel by viewModels()
    MainScreen(viewModel.viewState.collectAsState()) // Or pass in separate arguments
}

@Preview
@Composable
fun MainScreen(viewState: ViewState) {
    // display things
}

[Joost Klitsie]

This also makes your composables less platform specific

[sindrenm]

I think you mixed up a couple of things in that last example? @Preview should probably be on the first composable, and its function name would need to be different. simple smile