android-native-dev

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

3.8 Logging Level Usage

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

// ❌ 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

// 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

// ❌ 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+):

<!-- 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:

<!-- ❌ 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>

// ❌ 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

<!-- ❌ 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

• Read the complete error message first: Locate file and line number

• Check recent changes: Problems usually in latest modifications

• Clean Build: ./gradlew clean assembleDebug

• Check dependency versions: Version conflicts are common causes

• Refresh dependencies if needed: Clear cache and rebuild

6.3 Debugging Commands

# 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 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

Animation & Transitions Motion System

Accessibility Guidelines Accessibility

Large Screens & Foldables Adaptive Screens

Android Vitals & Performance Performance & Stability

Privacy & Security Privacy & Security

Audio, Video, Notifications Functional Requirements

App Style by Category Design Style Guide

8. Testing

Note: Only add test dependencies when the user explicitly asks for testing.

A well-tested Android app uses layered testing: fast local unit tests for logic, instrumentation tests for UI and integration, and Gradle Managed Devices to run emulators reproducibly on any machine — including CI.

8.1 Test Dependencies

Before adding test dependencies, inspect the project's existing versions to avoid conflicts:

• Check gradle/libs.versions.toml — if present, add test deps using the project's version catalog style

• Check existing build.gradle.kts for already-pinned dependency versions

• Match version families using the table below

Version Alignment Rules:

Test Dependency Must Align With How to Check

kotlinx-coroutines-test Project's kotlinx-coroutines-core version Search for kotlinx-coroutines in build files or version catalog

compose-ui-test-junit4 Project's Compose BOM or compose-compiler Search for compose-bom or compose.compiler in build files

espresso-* All Espresso artifacts must use the same version Search for espresso in build files

androidx.test:runner, rules, ext:junit Should use compatible AndroidX Test versions Search for androidx.test in build files

mockk Must support the project's Kotlin version Check kotlin version in root build.gradle.kts or version catalog

Dependencies Reference — add only the groups you need:

dependencies {
    // --- Local unit tests (src/test/) ---
    testImplementation("junit:junit:<version>")                          // 4.13.2+
    testImplementation("org.robolectric:robolectric:<version>")          // 4.16.1+
    testImplementation("io.mockk:mockk:<version>")                      // match Kotlin version
    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:<version>")  // match coroutines-core
    testImplementation("androidx.arch.core:core-testing:<version>")      // InstantTaskExecutorRule for LiveData
    testImplementation("app.cash.turbine:turbine:<version>")             // Flow/StateFlow testing

    // --- Instrumentation tests (src/androidTest/) ---
    androidTestImplementation("androidx.test.ext:junit:<version>")
    androidTestImplementation("androidx.test:runner:<version>")
    androidTestImplementation("androidx.test:rules:<version>")
    androidTestImplementation("androidx.test.espresso:espresso-core:<version>")
    androidTestImplementation("androidx.test.espresso:espresso-contrib:<version>")   // RecyclerView, Drawer
    androidTestImplementation("androidx.test.espresso:espresso-intents:<version>")   // Intent verification
    androidTestImplementation("androidx.test.espresso:espresso-idling-resource:<version>")
    androidTestImplementation("androidx.test.uiautomator:uiautomator:<version>")

    // --- Compose UI tests (only if project uses Compose) ---
    androidTestImplementation("androidx.compose.ui:ui-test-junit4")      // version from Compose BOM
    debugImplementation("androidx.compose.ui:ui-test-manifest")          // required for createComposeRule
}

Note: If the project uses a Compose BOM, ui-test-junit4 and ui-test-manifest don't need explicit versions — the BOM manages them.

Enable Robolectric resource support in the android block:

android {
    testOptions {
        unitTests.isIncludeAndroidResources = true  // required for Robolectric
    }
}

8.2 Testing by Layer

Layer Location Runs On Speed Use For

Unit (JUnit) src/test/ JVM ~ms ViewModels, repos, mappers, validators

Unit + Robolectric src/test/ JVM + simulated Android ~100ms Code needing Context, resources, SharedPrefs

Compose UI (local) src/test/ JVM + Robolectric ~100ms Composable rendering & interaction

Espresso src/androidTest/ Device/Emulator ~seconds View-based UI flows, Intents, DB integration

Compose UI (device) src/androidTest/ Device/Emulator ~seconds Full Compose UI flows with real rendering

UI Automator src/androidTest/ Device/Emulator ~seconds System dialogs, notifications, multi-app

Managed Device src/androidTest/ Gradle-managed AVD ~minutes (first run) CI, matrix testing across API levels

See Testing for detailed examples, code patterns, and Gradle Managed Device configuration.

8.3 Testing Commands

# Local unit tests (fast, no emulator)
./gradlew test                          # all modules
./gradlew :app:testDebugUnitTest        # app module, debug variant

# Single test class
./gradlew :app:testDebugUnitTest --tests "com.example.myapp.CounterViewModelTest"

# Instrumentation tests (requires device or managed device)
./gradlew connectedDebugAndroidTest     # on connected device
./gradlew pixel6Api34DebugAndroidTest   # on managed device

# Both together
./gradlew test connectedDebugAndroidTest

# Test with coverage report (JaCoCo)
./gradlew testDebugUnitTest jacocoTestReport

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