Understanding Themes in Jetpack Compose for Better UI

Jetpack Compose has revolutionized Android development, providing a modern, declarative approach to building user interfaces. While creating visually stunning and functional UIs is simpler than ever, understanding how to use theming effectively in Compose is essential for building scalable, maintainable, and cohesive applications. This post dives deep into the theming system in Jetpack Compose, offering advanced insights, best practices, and techniques for intermediate to advanced Android developers.

What is Theming in Jetpack Compose?

Theming in Jetpack Compose refers to defining and applying a consistent look and feel across your application’s user interface. Unlike the traditional XML-based approach in View systems, Jetpack Compose uses Kotlin’s type-safe APIs to define themes. This declarative approach enhances readability, flexibility, and integration with business logic.

At its core, theming revolves around the MaterialTheme composable, which provides:

  1. Typography: Text styles (e.g., headings, body text).

  2. Color: Primary, secondary, background, surface, and more.

  3. Shape: Corner shapes for components (e.g., buttons, cards).

By customizing these three aspects, you can create unique, brand-aligned designs for your application.

The Building Blocks of Jetpack Compose Themes

1. MaterialTheme

MaterialTheme is the foundational element for theming in Jetpack Compose. It wraps your composables and applies the defined theme values to its children.

@Composable
fun MyApp() {
    MaterialTheme(
        colors = lightColorPalette,
        typography = myTypography,
        shapes = myShapes
    ) {
        // Content here
    }
}

2. ColorScheme

ColorScheme defines the color palette for your application. Jetpack Compose supports dynamic theming with Material 3 (M3), which adapts your app’s colors to the user’s wallpaper. You can still create a static palette if preferred.

Example of a custom light color palette:

private val lightColorPalette = lightColorScheme(
    primary = Color(0xFF6200EE),
    onPrimary = Color.White,
    secondary = Color(0xFF03DAC6),
    onSecondary = Color.Black,
    background = Color.White,
    onBackground = Color.Black,
    surface = Color.White,
    onSurface = Color.Black
)

3. Typography

Typography plays a vital role in enhancing readability and aesthetics. Jetpack Compose uses Typography to manage text styles such as headers, captions, and body text. You can customize it as follows:

private val myTypography = Typography(
    headline1 = TextStyle(
        fontFamily = FontFamily.Default,
        fontWeight = FontWeight.Bold,
        fontSize = 30.sp
    ),
    body1 = TextStyle(
        fontFamily = FontFamily.Serif,
        fontWeight = FontWeight.Normal,
        fontSize = 16.sp
    )
)

4. Shapes

Shapes define the geometry of UI components, such as buttons, dialogs, and cards. The Shapes object enables customization of these corner shapes:

private val myShapes = Shapes(
    small = RoundedCornerShape(4.dp),
    medium = RoundedCornerShape(8.dp),
    large = RoundedCornerShape(16.dp)
)

Best Practices for Theming in Jetpack Compose

1. Separate Theme Definitions from Application Logic

Maintain theme definitions in a dedicated file to improve code readability and modularity. For instance:

- theme/
  - Color.kt
  - Typography.kt
  - Shape.kt
  - Theme.kt

2. Use Dynamic Color (Material 3)

Dynamic theming provides a personalized experience by adapting colors to the user’s device settings. To implement dynamic theming:

@Composable
fun MyApp() {
    val dynamicColors = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
        dynamicLightColorScheme(LocalContext.current)
    } else {
        lightColorPalette
    }

    MaterialTheme(
        colorScheme = dynamicColors,
        typography = myTypography,
        shapes = myShapes
    ) {
        // Content here
    }
}

3. Define Custom Attributes

Extend your theme by adding custom attributes. For example:

data class CustomColors(val customBackground: Color)

val LocalCustomColors = staticCompositionLocalOf { CustomColors(Color.Unspecified) }

@Composable
fun MyTheme(content: @Composable () -> Unit) {
    val customColors = CustomColors(Color(0xFFEDE7F6))

    CompositionLocalProvider(LocalCustomColors provides customColors) {
        MaterialTheme(content = content)
    }
}

val customBackground: Color
    @Composable get() = LocalCustomColors.current.customBackground

4. Support Dark Mode

Designing for both light and dark themes ensures accessibility and user satisfaction. Implement dark mode as follows:

val darkColorPalette = darkColorScheme(
    primary = Color(0xFFBB86FC),
    onPrimary = Color.Black,
    background = Color.Black,
    onBackground = Color.White,
    surface = Color.DarkGray,
    onSurface = Color.White
)

@Composable
fun MyApp() {
    val colors = if (isSystemInDarkTheme()) darkColorPalette else lightColorPalette

    MaterialTheme(
        colorScheme = colors,
        typography = myTypography,
        shapes = myShapes
    ) {
        // Content here
    }
}

Advanced Use Cases for Jetpack Compose Themes

1. Dynamic Runtime Theme Updates

Allow users to switch themes dynamically (e.g., light/dark mode toggle):

@Composable
fun MyApp(darkTheme: Boolean) {
    val colors = if (darkTheme) darkColorPalette else lightColorPalette

    MaterialTheme(
        colorScheme = colors,
        typography = myTypography,
        shapes = myShapes
    ) {
        // Content here
    }
}

2. Theming for Multimodal Applications

For apps supporting multiple device types (e.g., phones, tablets, or foldables), define responsive themes:

val screenSize = LocalConfiguration.current.screenWidthDp
val shapes = if (screenSize < 600) smallShapes else largeShapes

MaterialTheme(shapes = shapes) {
    // Content
}

3. Custom Animations in Themes

Integrate animations into themes to enhance user experience. For instance:

val transition = updateTransition(targetState = isDarkTheme, label = "ThemeTransition")
val backgroundColor by transition.animateColor(label = "BackgroundColor") { dark ->
    if (dark) Color.Black else Color.White
}

MaterialTheme(
    colors = lightColorPalette.copy(background = backgroundColor)
) {
    // Content
}

Conclusion

Mastering theming in Jetpack Compose unlocks the ability to create visually appealing, brand-consistent, and user-friendly interfaces. By leveraging the tools and best practices discussed in this post, developers can craft scalable and dynamic themes that cater to diverse user preferences and device configurations.

As Jetpack Compose evolves, staying up-to-date with new features like Material 3 and dynamic theming ensures your applications remain modern and competitive in the ever-changing landscape of Android development. Dive into theming today and elevate your Compose skills to the next level!