android - Jetpack Compose "onSurface"颜色不起作用

Question

我正在使用 Jetpack Compose 使用 Material Theming 进行测试，但我不确定为什么我不能制作主题的 onSurface色彩工作。
这里是 Theme.kt与 onSurface颜色设置为 Color.Red :

private val DarkColorPalette = darkColors(
    primary = Purple200,
    primaryVariant = Purple700,
    secondary = Teal200,
    onSurface = Color.Red, // <------- HERE
    onPrimary = Color.Blue, // <----- HERE
)

private val LightColorPalette = lightColors(
    primary = Purple500,
    primaryVariant = Purple700,
    secondary = Teal200,
    onSurface = Color.Red, // <------- AND HERE
    onPrimary = Color.Blue, // <----- HERE
)

@Composable
fun ExploringMaterialTheme(
    darkTheme: Boolean = isSystemInDarkTheme(),
    content: @Composable() () -> Unit
) {
    val colors = if (darkTheme) {
        DarkColorPalette
    } else {
        LightColorPalette
    }

    MaterialTheme(
        colors = colors,
        typography = Typography,
        shapes = Shapes,
        content = content
    )
}

这是 Activity :

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyApp()
        }
    }
}

@Preview
@Composable
fun MyApp() {
    ExploringMaterialTheme {
        // I also tried
        // Surface(color = MaterialTheme.colors.surface) {
        Surface {
            Text(text = "Hello!!", modifier = Modifier.padding(16.dp))
        }
    }
}

我期待“你好!!”以红色显示，而是以正常黑色显示。有什么我想念的想法吗？ 🤔

当我在 Surface 中设置颜色时，它可以正常工作零件。 Surface获得权利 on颜色(本例中为 onPrimary):

        Surface(color = MaterialTheme.colors.primary) {
            Text(text = "Hello!!", modifier = Modifier.padding(16.dp))
        }

Answer 1

Surface可组合用途:

CompositionLocalProvider(
        LocalContentColor provides contentColor){
            //
            content()
}

contentColor定义为:

fun Colors.contentColorFor(backgroundColor: Color): Color {
    return when (backgroundColor) {
    primary -> onPrimary
    primaryVariant -> onPrimary
    secondary -> onSecondary
    secondaryVariant -> onSecondary
    background -> onBackground
    surface -> onSurface
    error -> onError
    else -> Color.Unspecified
    }
}

目前您必须指定 surface 在您的主题中着色:

private val LightColorPalette = lightColors(
    primary = Blue500,
    surface = Color.Yellow)

在这种情况下， Text使用 onSurface颜色。
如果不指定 surface给 Surface 上色组件使用 background作为 colorBackground 和 onBackground对于 Text .