Styles

Limitations

• Warn the user that this skill is EXPERIMENTAL and requires updating to alpha version of Compose and opting in to the Experimental APIs.
• This skill only supports custom UI components and custom themes.
• This skill does not support Material Design component Styles.

Prerequisites

1. Upgrade dependencies

• The project must use compileSdk version 37 or higher.
• The project must use androidx.compose.foundation:foundation version 1.12.0-alpha01 or higher.
• Alternatively, the project must use Compose BOM version 2026.04.01 or higher.
• The API requires this exact package: import androidx.compose.foundation.style.Style

2. Configure compiler options to enable experimental API

You must opt-in to the experimental API at the project level. Add the following block to your module's build.gradle.kts:

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kotlin {
    compilerOptions {
        jvmTarget = JvmTarget.fromTarget("17")
        freeCompilerArgs.add("-opt-in=androidx.compose.foundation.style.ExperimentalFoundationStyleApi")
    }
}

Core workflows and guides

Refer to the official documentation to complete specific development tasks:

• Basic Style Usage: To set backgrounds, sizes, and alignments on a component, follow the Compose Styles Fundamentals Guide.
• State and Transitions: To configure property changes for state shifts (like pressed or hovered), follow the Animations and State-Based Styling Guide.
• Architecture Trade offs: To decide when to use a Style versus a standard Modifier, follow the Styles versus Modifiers Comparison.
• Theme Level Integration: To connect style definitions with custom themes, follow Theming with Styles and Custom Themes in Compose.

Step-by-Step Migration Workflow

Step 1: Analyze theme structure

1. Locate your central theme file (such as Theme.kt).
2. Identify design tokens. Note references for colors, typography, and shapes (for example, LocalColorScheme, LocalTypography, or LocalShapes).
3. If the project lacks Jetpack Compose dependencies, stop. Instruct the user to migrate to Jetpack Compose first.
4. If the project imports androidx.compose.material.MaterialTheme, recommend migrating to Material 3 before proceeding.

Step 2: Establish ComponentStyles

1. Create a new file named ComponentStyles.kt in your theme directory.

2. Define a top-level data class to hold your component styles, for example, the Jetsnack one is called JetsnackStyles:

   kotlinCopy code
   object ExampleComponentStyles {
       val customButtonStyle: Style = {
   
       }
       val customTextFieldStyle: Style = {
   
       }
   }
   

3. Expose this class through your custom theme with a static reference, don't use CompositionLocals here as it's not required.

   kotlinCopy code
   @Immutable
   class JetsnackTheme(
       // other Design system properties
   ) {
       companion object {
           val colors: CustomThemingWithStyles.JetsnackColors
               @Composable @ReadOnlyComposable
               get() = LocalJetsnackTheme.current.colors
           // ...
   
           // add helper static reference
           val styles: ComponentStyles = ComponentStyles
       }
   }
   

4. Provide extensions on StyleScope to reference theme tokens directly if they are exposed using CompositionLocals. For example:

   kotlinCopy code
   val StyleScope.colors: JetsnackColors
       get() = LocalJetsnackTheme.currentValue.colors
   
   val StyleScope.typography: androidx.compose.material3.Typography
       get() = LocalJetsnackTheme.currentValue.typography
   
   val StyleScope.shapes: Shapes
       get() = LocalJetsnackTheme.currentValue.shapes
   

Step 3: Migrate a component to Styles API

For each custom component (for example, CustomButton), complete the following sequence:

1. Establish a visual baseline (If an emulator is available):
   • If you CANNOT run an Android emulator: Skip this step entirely and proceed to Step 2.
   • If you CAN run an Android emulator: Perform the following to capture a baseline screenshot:
     • Option A: Locate and run an existing screenshot test for the component.
     • Option B (If no test exists): Create a test using the project's existing testing framework, then run it.
     • Option C (If no framework exists): Create a minimal screenshot test using UI Automator or Espresso, then run it.
2. Remove individual styling parameters : Remove styling parameters such as backgroundColor, shape, textStyle, and contentPadding from the signature - anything that StyleScope supports.
3. Add the style parameter : Add style: Style = Style to the function signature. Always ensure the default value is exactly Style (e.g., style: Style = Style) and not a specific style default like ChipStyleDefault or any other value.
4. Declare state tracking : If the component is interactable, create a MutableStyleState using the interaction source. Update state fields (such as isEnabled) inside the Composable to track the state correctly.
5. Apply styleable modifier : Replace specific layout modifiers on the root element with Modifier.styleable().
6. Move defaults to ComponentStyles : Move hardcoded values from the component definition to a dedicated Style instance in ComponentStyles.kt.
7. Validate component: Compare the baseline screenshot image taken at the start with the rendered Compose Preview of the new composable. Ignore string content; focus on layout and styling. Iterate on the Compose code until visual parity is achieved. Once verified, write a Compose UI test for the new composable.

Migration example

Before Migration:

kotlinCopy code
@Composable
fun CustomButton(
    onClick: () -> Unit,
    modifier: Modifier = Modifier,
    backgroundColor: Color = JetsnackTheme.colors.brandLight,
    disabledBackgroundColor: Color = JetsnackTheme.colors.brandSecondary,
    shape: Shape = JetsnackTheme.shapes.extraLarge,
    textStyle: TextStyle = JetsnackTheme.typography.labelLarge,
    enabled: Boolean = true,
    content: @Composable RowScope.() -> Unit,
) {
    val interactionSource = remember { MutableInteractionSource() }
    Row(
        modifier
            .clickable(onClick = onClick, indication = null, interactionSource = interactionSource)
            .background(if (enabled) backgroundColor else disabledBackgroundColor, shape)
            .defaultMinSize(58.dp, 40.dp),
        horizontalArrangement = Arrangement.Center,
        verticalAlignment = Alignment.CenterVertically,
        content = content,
    )
}

After Migration:

kotlinCopy code
// Exposed via ComponentStyles.kt
object ComponentStyles {
    val buttonStyle = Style {
        background(colors.brandLight)
        shape(shapes.extraLarge)
        minWidth(58.dp)
        minHeight(40.dp)
        textStyle(typography.labelLarge)
        disabled {
            background(colors.brandSecondary)
        }
    }
}

@Composable
fun CustomButton(
    onClick: () -> Unit,
    modifier: Modifier = Modifier,
    style: Style = Style,
    enabled: Boolean = true,
    content: @Composable RowScope.() -> Unit,
) {
    val interactionSource = remember { MutableInteractionSource() }
    val styleState = rememberUpdatedStyleState(interactionSource) {
        it.isEnabled = enabled
    }
    Row(
        modifier
            .clickable(onClick = onClick, indication = null, interactionSource = interactionSource)
            .styleable(styleState, JetsnackTheme.styles.buttonStyle, style),
        horizontalArrangement = Arrangement.Center,
        verticalAlignment = Alignment.CenterVertically,
        content = content,
    )
}

Step 4: Validate Changes

1. Build the project. Verify that there are no compilation errors.
2. Run your module's screenshot tests.
3. Compare visual outputs of the whole app between the previous and updated components. Verify that no visual layout regressions occur.