Found a reproducible(?) case of preview not working. Basically just using a color from a custom them...

# compose

[Colton Idle]

Found a reproducible(?) case of preview not working. Basically just using a color from a custom theme as a background causes preview to fail. Code in thread.

Stacktrace snippet:

Render Problem
java.lang.IllegalStateException: No RollerToasterColorPalette provided   at com.rollertoaster.app.theme.ThemeKt$AmbientRollerToasterColors$1.invok

[Colton Idle]

Fails:

@Preview
@Composable
fun MyPrev() {
    Column(
        modifier = Modifier
            .background(color = RollerToasterTheme.colors.main_1)
            .fillMaxWidth(1F)
    ) {
        Text("asdf")
    }
}

Works:

@Preview
@Composable
fun MyPrev() {
    Column(
        modifier = Modifier
            .fillMaxWidth(1F)
    ) {
        Text("asdf")
    }
}

[Albert Chang]

You can't expect your theme to work if you don't include the theme composable in the preview.

[Colton Idle]

Oof. For some reason... I did not know what. I feel like that maybe shouldn't compile or something? Idk. I understand it's valid code and so having it compile makes sense, but I totally did not get the feeling that I had to wrap it in my theme. I guess I haven't wrapped any of my previews in my theme

[jim]

This is one of the reasons you should avoid ambients - they create implicit dependencies that aren't tracked by the compiler. Of course, they're a little hard to avoid when material theme is an ambient 😔. But as a general rule. This is actually one of the less-bad failures; sometimes the issues are a lot more subtle.

I pushed pretty hard for ambients to be tracked by the compiler. Maybe some day we will have a different feature which provides similar capabilities but is more safe in a variety of ways.

[Chris Sinco [G]]

Yes right now functions shown in Preview need the app themes to be included/wrapped since otherwise it defaults to MaterialTheme. We've considered how to make this clearer but haven't resolved it yet.

[Colton Idle]

@Chris Sinco [G] is there an issue I can star?

[Chris Sinco [G]]

I can’t seem to find it on the public tracker as a feature request, so if you can, please file it to this component on Issue Tracker: Compose Preview

[Colton Idle]

Compose Preview is locked btw @Chris Sinco [G]

But filed here: https://issuetracker.google.com/issues/184759538

[Chris Sinco [G]]

Fun 🙂 Alright let me triage - thanks for filing!