Compose Multiplatform Theming: Cross-Platform UI Consistency with Jetpack Compose

Jetpack Compose is revolutionizing UI development across platforms, including Android, desktop, and web, through its Compose Multiplatform initiative. Consistent and cohesive theming is paramount to creating a polished, unified user experience regardless of the deployment target. This comprehensive guide will explore theming in Compose Multiplatform, covering custom themes, dark/light mode implementations, platform-specific adaptations, and best practices to achieve a visually harmonious and user-friendly application across various environments.

Understanding Compose Multiplatform Theming

Theming in Jetpack Compose revolves around creating a design system that defines the visual appearance of your application. This encompasses colors, typography, shapes, and other visual elements. In a multiplatform environment, effective theming ensures that these elements are consistent yet adapt appropriately to the nuances of each platform. Jetpack Compose’s MaterialTheme composable provides the foundational building blocks for theming. In the following sections, we will explore creating platform-agnostic themes with variations.

Benefits of Compose Multiplatform Theming

• Consistent Brand Identity: Ensures your application reflects a unified visual brand across all supported platforms, improving user recognition and trust.
• Simplified Maintenance: Centralized theme definitions reduce duplication and make visual updates and branding changes more manageable across the entire application.
• Enhanced User Experience: Provides a cohesive look and feel, promoting intuitive navigation and user satisfaction, regardless of whether they are using the app on their phone, desktop, or web browser.
• Code Reusability: Leverages shared codebase for theming logic and definitions, minimizing platform-specific code and improving maintainability.

Key Concepts for Theming in Compose Multiplatform

• Material Theme: The core building block for theming in Jetpack Compose, providing pre-defined color palettes, typography styles, and shapes that can be customized.
• Custom Themes: Creating and applying a custom theme to tailor the appearance to align with your brand’s style guide and create unique visual elements.
• Color Palette: Defining color schemes (primary, secondary, background, etc.) to create visually balanced themes with easy modification across different modes or platform adjustments.
• Typography: Setting text styles like font families, font sizes, font weights, and line heights for headers, body text, and captions, ensuring a consistent typography design across platforms.
• Shapes: Specifying the rounding, borders, and corners for UI elements like buttons, cards, and text fields to control the shape and visual emphasis of elements in your application.
• Dark and Light Modes: Implementing support for both dark and light color schemes within your theme and letting the system or the user easily toggle between the two for flexibility and readability under varying lighting conditions.
• Platform-Specific Adaptations: Customizing theming on different platforms to accommodate usability norms and styles appropriate to that environment while maintaining theme cohesion.

Implementing a Custom Theme in Compose Multiplatform

Step 1: Define Custom Colors, Typography, and Shapes

Create Kotlin files for defining your custom colors, typography, and shapes. Start by defining your color palette in a Colors.kt file. This will include setting the color variables in both Light and Dark modes to accommodate preferences by your end-users, who can manually set a preference or let the mobile or desktop OS dictate the preference in system settings:

// Colors.kt
import androidx.compose.ui.graphics.Color

object AppColors {
    object Light {
        val primary = Color(0xFF6200EE)
        val onPrimary = Color.White
        val secondary = Color(0xFF03DAC5)
        val onSecondary = Color.Black
        val background = Color.White
        val onBackground = Color.Black
        val surface = Color.White
        val onSurface = Color.Black
    }

    object Dark {
        val primary = Color(0xFFBB86FC)
        val onPrimary = Color.Black
        val secondary = Color(0xFF03DAC5)
        val onSecondary = Color.Black
        val background = Color(0xFF121212)
        val onBackground = Color.White
        val surface = Color(0xFF121212)
        val onSurface = Color.White
    }
}

Next, define typography using TextStyle. This should go into a separate file called Typography.kt:

// Typography.kt
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.text.font.FontFamily
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.unit.sp

object AppTypography {
    val h1 = TextStyle(
        fontFamily = FontFamily.Default,
        fontWeight = FontWeight.Bold,
        fontSize = 32.sp
    )

    val body1 = TextStyle(
        fontFamily = FontFamily.Default,
        fontWeight = FontWeight.Normal,
        fontSize = 16.sp
    )
}

Also specify shape attributes into a file labeled Shapes.kt to provide continuity and consistent stylization in components like buttons:

// Shapes.kt
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.ui.unit.dp

object AppShapes {
    val small = RoundedCornerShape(4.dp)
    val medium = RoundedCornerShape(8.dp)
    val large = RoundedCornerShape(16.dp)
}

Step 2: Create a Custom Theme Composable

Implement a custom theme composable that sets the MaterialTheme colors, typography, and shapes. Make sure to provide a boolean flag that specifies a check on Light or Dark mode to make themes easier to switch between when running:

// Theme.kt
import androidx.compose.foundation.isSystemInDarkTheme
import androidx.compose.material.MaterialTheme
import androidx.compose.material.Shapes
import androidx.compose.material.Typography
import androidx.compose.material.darkColors
import androidx.compose.material.lightColors
import androidx.compose.runtime.Composable

@Composable
fun AppTheme(darkTheme: Boolean = isSystemInDarkTheme(), content: @Composable () -> Unit) {
    val colors = if (darkTheme) {
        darkColors(
            primary = AppColors.Dark.primary,
            onPrimary = AppColors.Dark.onPrimary,
            secondary = AppColors.Dark.secondary,
            onSecondary = AppColors.Dark.onSecondary,
            background = AppColors.Dark.background,
            onBackground = AppColors.Dark.onBackground,
            surface = AppColors.Dark.surface,
            onSurface = AppColors.Dark.onSurface
        )
    } else {
        lightColors(
            primary = AppColors.Light.primary,
            onPrimary = AppColors.Light.onPrimary,
            secondary = AppColors.Light.secondary,
            onSecondary = AppColors.Light.onSecondary,
            background = AppColors.Light.background,
            onBackground = AppColors.Light.onBackground,
            surface = AppColors.Light.surface,
            onSurface = AppColors.Light.onSurface
        )
    }

    MaterialTheme(
        colors = colors,
        typography = Typography(), // You can use custom Typography as well
        shapes = Shapes(),   // You can use custom Shapes as well
        content = content
    )
}

Step 3: Apply the Custom Theme to Your Application

Wrap the root composable of your application with the AppTheme composable.

import androidx.compose.material.Text
import androidx.compose.runtime.Composable

@Composable
fun AppContent() {
    Text("Hello, Multiplatform!")
}

@Composable
fun MainView() {
    AppTheme {
        AppContent()
    }
}

Dark and Light Mode Implementation

Jetpack Compose makes implementing dark and light mode seamless using the isSystemInDarkTheme() composable function. When integrating into Theme.kt for each component type such as buttons, backgrounds, text, etc., they dynamically update their color based on device setting or can provide a direct preference from user to immediately override.

Toggling Between Dark and Light Modes

To add a user-controlled switch for toggling themes in Compose Multiplatform, you can use mutable state:

import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.material.Switch
import androidx.compose.runtime.Composable
import androidx.compose.foundation.layout.*
import androidx.compose.material.Text
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp

@Composable
fun ThemeToggle() {
    val isDarkTheme = remember { mutableStateOf(false) }

    Row(
        modifier = Modifier
            .fillMaxWidth()
            .padding(16.dp),
        verticalAlignment = Alignment.CenterVertically,
        horizontalArrangement = Arrangement.SpaceBetween
    ) {
        Text(text = "Dark Mode")
        Switch(
            checked = isDarkTheme.value,
            onCheckedChange = { isDarkTheme.value = it }
        )
    }
}

Implementing Multiplatform Awareness

Multiplatform aware means theme can accommodate particular platforms to avoid having it look the same everywhere but offer a look and feel expected by users and OS style design expectations such as fonts or even how certain popups are shown and displayed for notifications:

import androidx.compose.runtime.Composable
import androidx.compose.ui.platform.LocalView

@Composable
fun PlatformSpecificTheme() {
    val view = LocalView.current

    if (view.context.packageName.contains("android")) {
        Text("Android-Specific Theme")
    } else if (view.javaClass.name.contains("DesktopPlatformView")) {
        Text("Desktop-Specific Theme")
    } else {
        Text("Unknown platform. Implement Web or Default Style")
    }
}

Advanced Theming Techniques

Using Custom Design Tokens

Design tokens are named values that represent visual design attributes like color, spacing, or typography. They serve as a source of truth for the UI, and allow theme components to stay easily modified. In Compose Multiplatform, design tokens centralize theming information. Start defining those properties for both mobile, web, and desktop and import them in any of the custom stylings previously written and have values associated with each when rendering based on screen sizes or OS types.

Dynamic Color

You can incorporate dynamic colors, generated either programmatically or retrieved from platform-level settings, into the custom themes in the mobile area. While not yet widely available across other desktop or web versions of the theme styling for components and templates, they will eventually catch up when system tools expose values with run time checks on device characteristics to render dynamic styling.

Accessibility

When the styling or templating are set in design token as constants to be rendered dynamically or retrieved to update when conditions happen on client’s app or in OS levels, provide alternative values accessible at both web (with CSS adjustments when using semantics/accessibility tags), desktop (which typically comes by default and exposed), or mobile using talkback APIs and expose the right labels on button’s state with conditions exposed and assigned at run time to talk about elements state if clicked by end user to confirm styling properties are used accordingly to guide. Accessibility, styling properties like sizes (buttons size/minimum fonts etc) and styles will go through them for continuous delivery of the UI look for apps created for platforms using Compose’s framework, components and layouts with dynamic stylization/conditional stylization set dynamically on web, desktop and mobile. Those strategies enhance usability for everyone accessing through web and OS versions.

Best Practices for Compose Multiplatform Theming

• Centralize Theme Definitions: Maintain all theme-related definitions in a single location to avoid duplication and simplify maintenance.
• Use Semantic Color Names: Assign semantic names (e.g., primary, secondary, background) rather than specific color codes to provide better clarity and facilitate easy theme switching.
• Plan for Dark and Light Modes: Design your themes with both dark and light modes in mind from the beginning. Test frequently to address issues for both visual schemes throughout your applications to be run anywhere.
• Automate: When styling requirements meet dynamic characteristics like size/responsiveness and platforms OS capabilities/expected, make tests using automated tools against real user to validate whether what end users on both mobile, web or desktop, can experience good, clear applications following both WCAG on accessibilities with visual themes dynamically stylized through dynamic adjustments applied by clients system set for user preferences set locally by devices at either run time when system sets for local conditions too to meet optimal expectations. Keep automations to avoid surprises and allow constant deliveries against what requirements sets with design and styling across multi platform and devices for constant end user experience
• Consider Platform Conventions: While striving for consistency, adapt certain UI elements to align with platform-specific conventions, such as adjusting font rendering and applying platform-native shape configurations where possible.
• Thorough Testing: Extensively test themes across all target platforms to ensure consistent visual experiences and correct behavior of accessibility elements. Use real end users on platforms OS/browser systems across phones/tablets desktops browsers to know how dynamic stylized adjustments set at constants can allow right delivery visual components meeting end users with any set platform across system properties dynamically handled through run conditions inside clients, servers through multiple scenarios that users uses the systems to get constant satisfaction and results by access through their application, dynamically set the same way with system.

Conclusion

Compose Multiplatform Theming allows you to craft visually consistent, user-friendly experiences across diverse environments. To streamline your theme consistency, establish foundational configurations within Compose architecture by customizing colors/fonts or forms from start, which is especially crucial when expanding across multiple applications running across a number of devices, sizes dynamically styled on several operating system configurations with platforms’ requirements at runtime while system access parameters and visual element consistency remain strong from users by continuous delivery through continuous evaluation through access levels in all ways. Proper planning, centralized management, multi-scheme mode accessibilities including web browser requirements by dynamically accessing on multi platform projects using platforms Compose delivers satisfaction by styling aspects across them easily and dynamic satisfaction to run tests against system.