android-design（安卓设计）

Android Design Skill

Expert knowledge of Material Design 3 for Jetpack Compose applications. This skill enforces design excellence, accessibility compliance, and performance best practices.

Core Principles

1. Material Design 3 Foundation

• Use semantic tokens, not hardcoded values
• Apply dynamic color for Android 12+
• Follow M3 shape scale (4dp extraSmall to 28dp extraLarge)
• Use elevation levels (0dp to 5 levels)

2. Accessibility First

• Minimum 48x48dp touch targets
• 4.5:1 contrast ratio for normal text
• Proper contentDescription on all interactive elements
• Support fontScale up to 200%

3. Performance Stability

• Mark data classes @Immutable or @Stable
• Use remember and derivedStateOf correctly
• Prefer LazyColumn over Column for lists
• Provide stable keys for list items

Typography Scale (15 Styles)

Usage Pattern

// GOOD - Semantic tokens
Text(
    text = "Welcome",
    style = MaterialTheme.typography.headlineLarge
)

// BAD - Hardcoded values
Text(
    text = "Welcome",
    fontSize = 32.sp,
    fontWeight = FontWeight.Normal
)

Color System

Key Colors (5 Primary)

1. Primary - Brand color, interactive elements
2. Secondary - Less prominent UI
3. Tertiary - Accents, special elements
4. Error - Error states
5. Neutral - Surfaces, backgrounds

Tonal Palettes (13 Tones)

Each key color generates: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, 100

Usage Pattern

// GOOD - Semantic tokens
Surface(color = MaterialTheme.colorScheme.surface) {
    Text(
        text = "Hello",
        color = MaterialTheme.colorScheme.onSurface
    )
}

// BAD - Hardcoded colors
Surface(color = Color(0xFFFAFAFA)) {
    Text(
        text = "Hello",
        color = Color.Black
    )
}

Dynamic Color (Android 12+)

val colorScheme = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
    if (darkTheme) dynamicDarkColorScheme(context)
    else dynamicLightColorScheme(context)
} else {
    if (darkTheme) DarkColorScheme
    else LightColorScheme
}

Shape Scale

Touch Targets

Requirements

• Minimum: 48x48dp (M3 requirement)
• Recommended: 48x48dp with 8dp spacing
• WCAG 2.2: 24x24 CSS px minimum (Level AA)

Implementation

// GOOD - Proper touch target
IconButton(
    onClick = { /* action */ },
    modifier = Modifier.minimumInteractiveComponentSize()
) {
    Icon(
        imageVector = Icons.Default.Close,
        contentDescription = "Close dialog"
    )
}

// BAD - No touch target guarantee
Icon(
    imageVector = Icons.Default.Close,
    modifier = Modifier
        .size(24.dp)
        .clickable { /* action */ }
)

Spacing Scale

Base unit: 4dp

DO / DON'T

State Management

DO: Hoist state to appropriate level

@Composable
fun SearchScreen(viewModel: SearchViewModel = viewModel()) {
    val query by viewModel.searchQuery.collectAsState()
    SearchBar(query = query, onQueryChange = viewModel::updateQuery)
}

DON'T: Create state in leaf composables

@Composable
fun SearchBar() {
    var query by remember { mutableStateOf("") } // Can't test, can't share
    TextField(value = query, onValueChange = { query = it })
}

Modifiers

DO: Create modifiers outside composable body

private val cardModifier = Modifier
    .fillMaxWidth()
    .padding(16.dp)

@Composable
fun MyCard() {
    Card(modifier = cardModifier) { /* content */ }
}

DON'T: Create modifiers inside composition

@Composable
fun MyCard() {
    Card(
        modifier = Modifier // Creates new object every recomposition
            .fillMaxWidth()
            .padding(16.dp)
    ) { /* content */ }
}

Collections

DO: Use immutable collections for stable recomposition

@Immutable
data class UiState(
    val items: ImmutableList<Item> = persistentListOf()
)

DON'T: Use mutable collections in state

data class UiState(
    val items: List<Item> = emptyList() // Unstable!
)

LazyColumn Keys

DO: Provide stable keys

LazyColumn {
    items(items, key = { it.id }) { item ->
        ItemRow(item)
    }
}

DON'T: Rely on index-based keys

LazyColumn {
    items(items.size) { index -> // Breaks on reorder
        ItemRow(items[index])
    }
}

Severity Levels

When auditing, classify issues as:

References

For detailed specifications, see:

• Material Design 3 Foundation
• Compose Anti-Patterns Database
• Compose Rules Integration
• Compiler Metrics Guide
• Now in Android Patterns
• Integration Guide