---
name: android-native-dev
description: Android native application development and UI design guide. Covers Material Design 3, Kotlin/Compose development, project configuration, accessibility, and build troubleshooting. Read this before Android native application development.
license: MIT
metadata:
  version: "1.0.0"
  category: mobile
  sources:
    - Material Design 3 Guidelines (material.io)
    - Android Developer Documentation (developer.android.com)
    - Google Play Quality Guidelines
    - WCAG Accessibility Guidelines
---

## 1. Project Scenario Assessment

Before starting development, assess the current project state:

| Scenario | Characteristics | Approach |
|----------|-----------------|----------|
| **Empty Directory** | No files present | Full initialization required, including Gradle Wrapper |
| **Has Gradle Wrapper** | `gradlew` and `gradle/wrapper/` exist | Use `./gradlew` directly for builds |
| **Android Studio Project** | Complete project structure, may lack wrapper | Check wrapper, run `gradle wrapper` if needed |
| **Incomplete Project** | Partial files present | Check missing files, complete configuration |

**Key Principles**:
- Before writing business logic, ensure `./gradlew assembleDebug` succeeds
- If `gradle.properties` is missing, create it first and configure AndroidX

### 1.1 Required Files Checklist

```
MyApp/
├── gradle.properties          # Configure AndroidX and other settings
├── settings.gradle.kts
├── build.gradle.kts           # Root level
├── gradle/wrapper/
│   └── gradle-wrapper.properties
├── app/
│   ├── build.gradle.kts       # Module level
│   └── src/main/
│       ├── AndroidManifest.xml
│       ├── java/com/example/myapp/
│       │   └── MainActivity.kt
│       └── res/
│           ├── values/
│           │   ├── strings.xml
│           │   ├── colors.xml
│           │   └── themes.xml
│           └── mipmap-*/       # App icons
```

---

## 2. Project Configuration

### 2.1 gradle.properties

```properties
# Required configuration
android.useAndroidX=true
android.enableJetifier=true

# Build optimization
org.gradle.parallel=true
kotlin.code.style=official

# JVM memory settings (adjust based on project size)
# Small projects: 2048m, Medium: 4096m, Large: 8192m+
# org.gradle.jvmargs=-Xmx4096m -Dfile.encoding=UTF-8
```

> **Note**: If you encounter `OutOfMemoryError` during build, increase `-Xmx` value. Large projects with many dependencies may require 8GB or more.

### 2.2 Dependency Declaration Standards

```kotlin
dependencies {
    // Use BOM to manage Compose versions
    implementation(platform("androidx.compose:compose-bom:2024.02.00"))
    implementation("androidx.compose.ui:ui")
    implementation("androidx.compose.material3:material3")
    
    // Activity & ViewModel
    implementation("androidx.activity:activity-compose:1.8.2")
    implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.7.0")
}
```

### 2.3 Build Variants & Product Flavors

Product Flavors allow you to create different versions of your app (e.g., free/paid, dev/staging/prod).

**Configuration in app/build.gradle.kts**:

```kotlin
android {
    // Define flavor dimensions
    flavorDimensions += "environment"
    
    productFlavors {
        create("dev") {
            dimension = "environment"
            applicationIdSuffix = ".dev"
            versionNameSuffix = "-dev"
            
            // Different config values per flavor
            buildConfigField("String", "API_BASE_URL", "\"https://dev-api.example.com\"")
            buildConfigField("Boolean", "ENABLE_LOGGING", "true")
            
            // Different resources
            resValue("string", "app_name", "MyApp Dev")
        }
        
        create("staging") {
            dimension = "environment"
            applicationIdSuffix = ".staging"
            versionNameSuffix = "-staging"
            
            buildConfigField("String", "API_BASE_URL", "\"https://staging-api.example.com\"")
            buildConfigField("Boolean", "ENABLE_LOGGING", "true")
            resValue("string", "app_name", "MyApp Staging")
        }
        
        create("prod") {
            dimension = "environment"
            // No suffix for production
            
            buildConfigField("String", "API_BASE_URL", "\"https://api.example.com\"")
            buildConfigField("Boolean", "ENABLE_LOGGING", "false")
            resValue("string", "app_name", "MyApp")
        }
    }
    
    buildTypes {
        debug {
            isDebuggable = true
            isMinifyEnabled = false
        }
        release {
            isDebuggable = false
            isMinifyEnabled = true
            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
        }
    }
}
```

**Build Variant Naming**: `{flavor}{BuildType}` → e.g., `devDebug`, `prodRelease`

**Gradle Build Commands**:

```bash
# List all available build variants
./gradlew tasks --group="build"

# Build specific variant (flavor + buildType)
./gradlew assembleDevDebug        # Dev flavor, Debug build
./gradlew assembleStagingDebug    # Staging flavor, Debug build
./gradlew assembleProdRelease     # Prod flavor, Release build

# Build all variants of a specific flavor
./gradlew assembleDev             # All Dev variants (debug + release)
./gradlew assembleProd            # All Prod variants

# Build all variants of a specific build type
./gradlew assembleDebug           # All flavors, Debug build
./gradlew assembleRelease         # All flavors, Release build

# Install specific variant to device
./gradlew installDevDebug
./gradlew installProdRelease

# Build and install in one command
./gradlew installDevDebug && adb shell am start -n com.example.myapp.dev/.MainActivity
```

**Access BuildConfig in Code**:

> **Note**: Starting from AGP 8.0, `BuildConfig` is no longer generated by default. You must explicitly enable it in your `build.gradle.kts`:
> ```kotlin
> android {
>     buildFeatures {
>         buildConfig = true
>     }
> }
> ```

```kotlin
// Use build config values in your code
val apiUrl = BuildConfig.API_BASE_URL
val isLoggingEnabled = BuildConfig.ENABLE_LOGGING

if (BuildConfig.DEBUG) {
    // Debug-only code
}
```

**Flavor-Specific Source Sets**:

```
app/src/
├── main/           # Shared code for all flavors
├── dev/            # Dev-only code and resources
│   ├── java/
│   └── res/
├── staging/        # Staging-only code and resources
├── prod/           # Prod-only code and resources
├── debug/          # Debug build type code
└── release/        # Release build type code
```

**Multiple Flavor Dimensions** (e.g., environment + tier):

```kotlin
android {
    flavorDimensions += listOf("environment", "tier")
    
    productFlavors {
        create("dev") { dimension = "environment" }
        create("prod") { dimension = "environment" }
        
        create("free") { dimension = "tier" }
        create("paid") { dimension = "tier" }
    }
}
// Results in: devFreeDebug, devPaidDebug, prodFreeRelease, etc.
```

---

## 3. Kotlin Development Standards

### 3.1 Naming Conventions

| Type | Convention | Example |
|------|------------|---------|
| Class/Interface | PascalCase | `UserRepository`, `MainActivity` |
| Function/Variable | camelCase | `getUserName()`, `isLoading` |
| Constant | SCREAMING_SNAKE | `MAX_RETRY_COUNT` |
| Package | lowercase | `com.example.myapp` |
| Composable | PascalCase | `@Composable fun UserCard()` |

### 3.2 Code Standards (Important)

**Null Safety**:
```kotlin
// ❌ Avoid: Non-null assertion !! (may crash)
val name = user!!.name

// ✅ Recommended: Safe call + default value
val name = user?.name ?: "Unknown"

// ✅ Recommended: let handling
user?.let { processUser(it) }
```

**Exception Handling**:
```kotlin
// ❌ Avoid: Random try-catch in business layer swallowing exceptions
fun loadData() {
    try {
        val data = api.fetch()
    } catch (e: Exception) {
        // Swallowing exception, hard to debug
    }
}

// ✅ Recommended: Let exceptions propagate, handle at appropriate layer
suspend fun loadData(): Result<Data> {
    return try {
        Result.success(api.fetch())
    } catch (e: Exception) {
        Result.failure(e)  // Wrap and return, let caller decide handling
    }
}

// ✅ Recommended: Unified handling in ViewModel
viewModelScope.launch {
    runCatching { repository.loadData() }
        .onSuccess { _uiState.value = UiState.Success(it) }
        .onFailure { _uiState.value = UiState.Error(it.message) }
}
```

### 3.3 Threading & Coroutines (Critical)

**Thread Selection Principles**:

| Operation Type | Thread | Description |
|----------------|--------|-------------|
| UI Updates | `Dispatchers.Main` | Update View, State, LiveData |
| Network Requests | `Dispatchers.IO` | HTTP calls, API requests |
| File I/O | `Dispatchers.IO` | Local storage, database operations |
| Compute Intensive | `Dispatchers.Default` | JSON parsing, sorting, encryption |

**Correct Usage**:
```kotlin
// In ViewModel
viewModelScope.launch {
    // Default Main thread, can update UI State
    _uiState.value = UiState.Loading
    
    // Switch to IO thread for network request
    val result = withContext(Dispatchers.IO) {
        repository.fetchData()
    }
    
    // Automatically returns to Main thread, update UI
    _uiState.value = UiState.Success(result)
}

// In Repository (suspend functions should be main-safe)
suspend fun fetchData(): Data = withContext(Dispatchers.IO) {
    api.getData()
}
```

**Common Mistakes**:
```kotlin
// ❌ Wrong: Updating UI on IO thread
viewModelScope.launch(Dispatchers.IO) {
    val data = api.fetch()
    _uiState.value = data  // Crash or warning!
}

// ❌ Wrong: Executing time-consuming operation on Main thread
viewModelScope.launch {
    val data = api.fetch()  // Blocking main thread! ANR
}

// ✅ Correct: Fetch on IO, update on Main
viewModelScope.launch {
    val data = withContext(Dispatchers.IO) { api.fetch() }
    _uiState.value = data
}
```

### 3.4 Visibility Rules

```kotlin
// Default is public, declare explicitly when needed
class UserRepository {           // public
    private val cache = mutableMapOf<String, User>()  // Visible only within class
    internal fun clearCache() {} // Visible only within module
}

// data class properties are public by default, be careful when used across modules
data class User(
    val id: String,       // public
    val name: String
)
```

### 3.5 Common Syntax Pitfalls

```kotlin
// ❌ Wrong: Accessing uninitialized lateinit
class MyViewModel : ViewModel() {
    lateinit var data: String
    fun process() = data.length  // May crash
}

// ✅ Correct: Use nullable or default value
class MyViewModel : ViewModel() {
    var data: String? = null
    fun process() = data?.length ?: 0
}

// ❌ Wrong: Using return in lambda
list.forEach { item ->
    if (item.isEmpty()) return  // Returns from outer function!
}

// ✅ Correct: Use return@forEach
list.forEach { item ->
    if (item.isEmpty()) return@forEach
}
```

### 3.6 Server Response Data Class Fields Must Be Nullable

```kotlin
// ❌ Wrong: Fields declared as non-null (server may not return them)
data class UserResponse(
    val id: String = "",
    val name: String = "",
    val avatar: String = ""
)

// ✅ Correct: All fields declared as nullable
data class UserResponse(
    @SerializedName("id")
    val id: String? = null,
    @SerializedName("name")
    val name: String? = null,
    @SerializedName("avatar")
    val avatar: String? = null
)
```

### 3.7 Lifecycle Resource Management

```kotlin
// ❌ Wrong: Only adding Observer, not removing
class MyView : View {
    override fun onAttachedToWindow() {
        super.onAttachedToWindow()
        activity?.lifecycle?.addObserver(this)
    }
    // Memory leak!
}

// ✅ Correct: Paired add and remove
class MyView : View {
    override fun onAttachedToWindow() {
        super.onAttachedToWindow()
        activity?.lifecycle?.addObserver(this)
    }

    override fun onDetachedFromWindow() {
        activity?.lifecycle?.removeObserver(this)
        super.onDetachedFromWindow()
    }
}
```

### 3.8 Logging Level Usage

```kotlin
import android.util.Log

// Info: Key checkpoints in normal flow
Log.i(TAG, "loadData: started, userId = $userId")

// Warning: Abnormal but recoverable situations
Log.w(TAG, "loadData: cache miss, fallback to network")

// Error: Failure/error situations
Log.e(TAG, "loadData failed: ${error.message}")
```

| Level | Use Case |
|-------|----------|
| `i` (Info) | Normal flow, method entry, key parameters |
| `w` (Warning) | Recoverable exceptions, fallback handling, null returns |
| `e` (Error) | Request failures, caught exceptions, unrecoverable errors |

---

## 4. Jetpack Compose Standards

### 4.1 @Composable Context Rules

```kotlin
// ❌ Wrong: Calling Composable from non-Composable function
fun showError(message: String) {
    Text(message)  // Compile error!
}

// ✅ Correct: Mark as @Composable
@Composable
fun ErrorMessage(message: String) {
    Text(message)
}

// ❌ Wrong: Using suspend outside LaunchedEffect
@Composable
fun MyScreen() {
    val data = fetchData()  // Error!
}

// ✅ Correct: Use LaunchedEffect
@Composable
fun MyScreen() {
    var data by remember { mutableStateOf<Data?>(null) }
    LaunchedEffect(Unit) {
        data = fetchData()
    }
}
```

### 4.2 State Management

```kotlin
// Basic State
var count by remember { mutableStateOf(0) }

// Derived State (avoid redundant computation)
val isEven by remember { derivedStateOf { count % 2 == 0 } }

// Persist across recomposition (e.g., scroll position)
val scrollState = rememberScrollState()

// State in ViewModel
class MyViewModel : ViewModel() {
    private val _uiState = MutableStateFlow(UiState())
    val uiState: StateFlow<UiState> = _uiState.asStateFlow()
}
```

### 4.3 Common Compose Mistakes

```kotlin
// ❌ Wrong: Creating objects in Composable (created on every recomposition)
@Composable
fun MyScreen() {
    val viewModel = MyViewModel()  // Wrong!
}

// ✅ Correct: Use viewModel() or remember
@Composable
fun MyScreen(viewModel: MyViewModel = viewModel()) {
    // ...
}
```

---

## 5. Resources & Icons

### 5.1 App Icon Requirements

Must provide multi-resolution icons:

| Directory | Size | Purpose |
|-----------|------|---------|
| mipmap-mdpi | 48x48 | Baseline |
| mipmap-hdpi | 72x72 | 1.5x |
| mipmap-xhdpi | 96x96 | 2x |
| mipmap-xxhdpi | 144x144 | 3x |
| mipmap-xxxhdpi | 192x192 | 4x |

Recommended: Use Adaptive Icon (Android 8+):

```xml
<!-- res/mipmap-anydpi-v26/ic_launcher.xml -->
<adaptive-icon>
    <background android:drawable="@color/ic_launcher_background"/>
    <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
</adaptive-icon>
```

### 5.2 Resource Naming Conventions

| Type | Prefix | Example |
|------|--------|---------|
| Layout | layout_ | `layout_main.xml` |
| Image | ic_, img_, bg_ | `ic_user.png` |
| Color | color_ | `color_primary` |
| String | - | `app_name`, `btn_submit` |

### 5.3 Avoid Android Reserved Names (Important)

Variable names, resource IDs, colors, icons, and XML elements **must not** use Android reserved words or system resource names. Using reserved names causes build errors or resource conflicts.

**Common Reserved Names to Avoid**:

| Category | Reserved Names (Do NOT Use) |
|----------|----------------------------|
| Colors | `background`, `foreground`, `transparent`, `white`, `black` |
| Icons/Drawables | `icon`, `logo`, `image`, `drawable` |
| Views | `view`, `text`, `button`, `layout`, `container` |
| Attributes | `id`, `name`, `type`, `style`, `theme`, `color` |
| System | `app`, `android`, `content`, `data`, `action` |

**Examples**:

```xml
<!-- ❌ Wrong: Using reserved names -->
<color name="background">#FFFFFF</color>
<color name="icon">#000000</color>

<!-- ✅ Correct: Add prefix or specific naming -->
<color name="app_background">#FFFFFF</color>
<color name="icon_primary">#000000</color>
```

```kotlin
// ❌ Wrong: Variable names conflict with system
val icon = R.drawable.my_icon
val background = Color.White

// ✅ Correct: Use descriptive names
val appIcon = R.drawable.my_icon
val screenBackground = Color.White
```

```xml
<!-- ❌ Wrong: Drawable name conflicts -->
<ImageView android:src="@drawable/icon" />

<!-- ✅ Correct: Add prefix -->
<ImageView android:src="@drawable/ic_home" />
```

---

## 6. Build Error Diagnosis & Fixes

### 6.1 Common Error Quick Reference

| Error Keyword | Cause | Fix |
|---------------|-------|-----|
| `Unresolved reference` | Missing import or undefined | Check imports, verify dependencies |
| `Type mismatch` | Type incompatibility | Check parameter types, add conversion |
| `Cannot access` | Visibility issue | Check public/private/internal |
| `@Composable invocations` | Composable context error | Ensure caller is also @Composable |
| `Duplicate class` | Dependency conflict | Use `./gradlew dependencies` to investigate |
| `AAPT: error` | Resource file error | Check XML syntax and resource references |

### 6.2 Fix Best Practices

1. **Read the complete error message first**: Locate file and line number
2. **Check recent changes**: Problems usually in latest modifications
3. **Clean Build**: `./gradlew clean assembleDebug`
4. **Check dependency versions**: Version conflicts are common causes
5. **Refresh dependencies if needed**: Clear cache and rebuild

### 6.3 Debugging Commands

```bash
# Clean and build
./gradlew clean assembleDebug

# View dependency tree (investigate conflicts)
./gradlew :app:dependencies

# View detailed errors
./gradlew assembleDebug --stacktrace

# Refresh dependencies
./gradlew --refresh-dependencies
```

---

## 7. Material Design 3 Guidelines

Review Android UI files for compliance with Material Design 3 Guidelines and Android best practices.

### Design Philosophy

#### M3 Core Principles

| Principle | Description |
|-----------|-------------|
| **Personal** | Dynamic color based on user preferences and wallpaper |
| **Adaptive** | Responsive across all screen sizes and form factors |
| **Expressive** | Bold colors and typography with personality |
| **Accessible** | Inclusive design for all users |

#### M3 Expressive (Latest)

The latest evolution adds emotion-driven UX through:
- Vibrant, dynamic colors
- Intuitive motion physics
- Adaptive components
- Flexible typography
- Contrasting shapes (35 new shape options)

### App Style Selection

**Critical Decision**: Match visual style to app category and target audience.

| App Category | Visual Style | Key Characteristics |
|--------------|--------------|---------------------|
| Utility/Tool | Minimalist | Clean, efficient, neutral colors |
| Finance/Banking | Professional Trust | Conservative colors, security-focused |
| Health/Wellness | Calm & Natural | Soft colors, organic shapes |
| Kids (3-5) | Playful Simple | Bright colors, large targets (56dp+) |
| Kids (6-12) | Fun & Engaging | Vibrant, gamified feedback |
| Social/Entertainment | Expressive | Brand-driven, gesture-rich |
| Productivity | Clean & Focused | Minimal, high contrast |
| E-commerce | Conversion-focused | Clear CTAs, scannable |

See [Design Style Guide](references/design-style-guide.md) for detailed style profiles.

### Quick Reference: Key Specifications

#### Color Contrast Requirements

| Element | Minimum Ratio |
|---------|---------------|
| Body text | **4.5:1** |
| Large text (18sp+) | **3:1** |
| UI components | **3:1** |

#### Touch Targets

| Type | Size |
|------|------|
| Minimum | 48 × 48dp |
| Recommended (primary actions) | 56 × 56dp |
| Kids apps | 56dp+ |
| Spacing between targets | 8dp minimum |

#### 8dp Grid System

| Token | Value | Usage |
|-------|-------|-------|
| xs | 4dp | Icon padding |
| sm | 8dp | Tight spacing |
| md | 16dp | Default padding |
| lg | 24dp | Section spacing |
| xl | 32dp | Large gaps |
| xxl | 48dp | Screen margins |

#### Typography Scale (Summary)

| Category | Sizes |
|----------|-------|
| Display | 57sp, 45sp, 36sp |
| Headline | 32sp, 28sp, 24sp |
| Title | 22sp, 16sp, 14sp |
| Body | 16sp, 14sp, 12sp |
| Label | 14sp, 12sp, 11sp |

#### Animation Duration

| Type | Duration |
|------|----------|
| Micro (ripples) | 50-100ms |
| Short (simple) | 100-200ms |
| Medium (expand/collapse) | 200-300ms |
| Long (complex) | 300-500ms |

#### Component Dimensions

| Component | Height | Min Width |
|-----------|--------|-----------|
| Button | 40dp | 64dp |
| FAB | 56dp | 56dp |
| Text Field | 56dp | 280dp |
| App Bar | 64dp | - |
| Bottom Nav | 80dp | - |

### Anti-Patterns (Must Avoid)

#### UI Anti-Patterns
- More than 5 bottom navigation items
- Multiple FABs on same screen
- Touch targets smaller than 48dp
- Inconsistent spacing (non-8dp multiples)
- Missing dark theme support
- Text on colored backgrounds without contrast check

#### Performance Anti-Patterns
- Startup time > 2 seconds without progress indicator
- Frame rate < 60 FPS (> 16ms per frame)
- Crash rate > 1.09% (Google Play threshold)
- ANR rate > 0.47% (Google Play threshold)

#### Accessibility Anti-Patterns
- Missing contentDescription on interactive elements
- Element type in labels (e.g., "Save button" instead of "Save")
- Complex gestures in kids apps
- Text-only buttons for non-readers

### Review Checklist

- [ ] 8dp spacing grid compliance
- [ ] 48dp minimum touch targets
- [ ] Proper typography scale usage
- [ ] Color contrast compliance (4.5:1+ for text)
- [ ] Dark theme support
- [ ] contentDescription on all interactive elements
- [ ] Startup < 2 seconds or shows progress
- [ ] Visual style matches app category

### Design References

| Topic | Reference |
|-------|-----------|
| Colors, Typography, Spacing, Shapes | [Visual Design](references/visual-design.md) |
| Animation & Transitions | [Motion System](references/motion-system.md) |
| Accessibility Guidelines | [Accessibility](references/accessibility.md) |
| Large Screens & Foldables | [Adaptive Screens](references/adaptive-screens.md) |
| Android Vitals & Performance | [Performance & Stability](references/performance-stability.md) |
| Privacy & Security | [Privacy & Security](references/privacy-security.md) |
| Audio, Video, Notifications | [Functional Requirements](references/functional-requirements.md) |
| App Style by Category | [Design Style Guide](references/design-style-guide.md) |
