android-native-dev

---

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

# 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

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:

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:

# 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:

android {
    buildFeatures {
        buildConfig = true
    }
}

// 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):

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:

// ❌ 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:

// ❌ 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:

// 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:

// ❌ 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

// 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

// ❌ 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

// ❌ 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

// ❌ 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 onDetache