Kotlin for Unity Developers: 5 Key Differences to Know

Difficulty Level: 🌟🌟 Intermediate

Hey there, Unity developer! 👋

Thinking about expanding into native Android development with Kotlin? First off, let me say you’re making a smart move! Your Unity C# experience puts you in an excellent position to pick up Kotlin, and honestly, the transition is smoother than most developers expect.

But I’ll be real with you—there are some key differences that can trip you up if you’re not aware of them. I remember my first week with Kotlin, confidently thinking “I know C#, how different can this be?” Well… let’s just say I spent a lot of time scratching my head wondering why my “obviously correct” code wasn’t working! 😅

💡 Encouraging Note: If you’ve mastered Unity’s C#, you already understand object-oriented programming, memory management, and mobile development constraints. Those are the hard parts! Kotlin is just a different way of expressing the same concepts you already know.

After years of developing both Unity games and native Android apps, including our VR puzzle game Pipe Craft and various mobile applications, I’ve helped numerous Unity developers successfully make this transition. Here’s what I’ve learned: many concepts transfer directly, but understanding where they differ will save you hours of frustration.

The good news? The learning curve isn’t as steep as you might think. The challenge? Knowing which familiar concepts work differently in Kotlin so you don’t get stuck on silly syntax issues.

Ready to add native Android development to your toolkit? Let’s explore the 5 most important differences that will make your transition smooth and confident!

Why Unity Developers Should Learn Kotlin

Before diving into the differences, let’s address why this transition makes sense:

Complementary Skills:

• Unity: Games, AR/VR experiences, cross-platform content
• Kotlin: Native Android apps, performance-critical mobile applications
• Combined: Full mobile development stack from games to productivity apps

Market Opportunities:

• Many clients need both game development AND native mobile apps
• Kotlin Multiplatform lets you share code between Android and iOS
• AR/VR often requires native mobile integration for companion apps

Technical Synergy:

• Both target mobile devices with performance constraints
• Similar object-oriented programming principles
• Both require understanding of mobile lifecycle management
• Performance optimization skills transfer well—concepts from Unity mobile performance management apply to native Android development

Difference 1: Null Safety - From Nullable References to Safe Calls

Unity C# Approach:

// C# - Null reference exceptions are runtime errors
public class PlayerController : MonoBehaviour {
    [SerializeField] private Transform targetTransform;
    [SerializeField] private AudioSource audioSource;
    
    private void Update() {
        // Potential NullReferenceException if targetTransform is null
        float distance = Vector3.Distance(transform.position, targetTransform.position);
        
        if (distance < 5f) {
            // Potential NullReferenceException if audioSource is null
            audioSource.Play();
        }
    }
}

Kotlin Approach:

// Kotlin - Null safety built into the type system
class GameManager {
    private var targetPosition: Vector3? = null
    private var audioPlayer: AudioPlayer? = null
    
    fun updateGame() {
        // Safe call operator - only executes if targetPosition is not null
        targetPosition?.let { target ->
            val distance = calculateDistance(currentPosition, target)
            
            if (distance < 5f) {
                // Safe call with Elvis operator for default behavior
                audioPlayer?.playSound() ?: showError("Audio unavailable")
            }
        }
    }
    
    private fun calculateDistance(pos1: Vector3, pos2: Vector3): Float {
        // Kotlin requires explicit null handling
        return sqrt((pos1.x - pos2.x).pow(2) + (pos1.y - pos2.y).pow(2))
    }
}

Key Takeaway: Kotlin forces you to handle null cases at compile time, preventing the runtime crashes that Unity developers often encounter with missing component references. However, many developers new to Kotlin make common null safety mistakes when transitioning from languages without built-in null safety. This becomes especially important when building Jetpack Compose UIs where null state can break your interface.

Difference 2: Properties - From Auto-Properties to Smart Accessors

Unity C# Approach:

// C# - Properties with backing fields
public class PlayerStats : MonoBehaviour {
    [SerializeField] private int health = 100;
    [SerializeField] private int maxHealth = 100;
    
    public int Health {
        get { return health; }
        set { 
            health = Mathf.Clamp(value, 0, maxHealth);
            OnHealthChanged?.Invoke(health);
        }
    }
    
    public float HealthPercentage {
        get { return (float)health / maxHealth; }
    }
    
    public UnityEvent<int> OnHealthChanged;
}

Kotlin Approach:

// Kotlin - Properties with custom getters/setters
class PlayerStats {
    var maxHealth: Int = 100
    
    var health: Int = 100
        set(value) {
            field = value.coerceIn(0, maxHealth) // Kotlin's version of Mathf.Clamp
            onHealthChanged?.invoke(field)
        }
    
    // Computed property - no backing field needed
    val healthPercentage: Float
        get() = health.toFloat() / maxHealth
    
    // Kotlin doesn't have UnityEvent, use function types instead
    var onHealthChanged: ((Int) -> Unit)? = null
}

// Usage
fun updatePlayerHealth() {
    val playerStats = PlayerStats()
    
    playerStats.onHealthChanged = { newHealth ->
        println("Health changed to: $newHealth")
        updateHealthBar(newHealth)
    }
    
    playerStats.health = 75 // Automatically triggers the setter
}

Key Takeaway: Kotlin properties are more concise than C# but work similarly. The main difference is using field instead of a private backing field.

Difference 3: Coroutines vs Unity Coroutines - Different But Familiar

Unity C# Approach:

// Unity Coroutines - yield-based with MonoBehaviour dependency
public class SpawnManager : MonoBehaviour {
    [SerializeField] private GameObject enemyPrefab;
    [SerializeField] private Transform spawnPoint;
    
    private void Start() {
        StartCoroutine(SpawnEnemiesRoutine());
    }
    
    private IEnumerator SpawnEnemiesRoutine() {
        while (true) {
            // Wait for specific conditions
            yield return new WaitForSeconds(2f);
            yield return new WaitUntil(() => CanSpawnEnemy());
            
            // Spawn enemy
            Instantiate(enemyPrefab, spawnPoint.position, spawnPoint.rotation);
            
            yield return null; // Wait one frame
        }
    }
    
    private bool CanSpawnEnemy() {
        return GameObject.FindGameObjectsWithTag("Enemy").Length < 5;
    }
}

Kotlin Approach:

// Kotlin Coroutines - suspend functions with structured concurrency
class SpawnManager {
    private val enemyPrefab: EnemyPrefab = EnemyPrefab()
    private val spawnPoint: Vector3 = Vector3(0f, 0f, 0f)
    
    // Launch coroutine in appropriate scope
    fun startSpawning(scope: CoroutineScope) {
        scope.launch {
            spawnEnemiesRoutine()
        }
    }
    
    private suspend fun spawnEnemiesRoutine() {
        while (true) {
            // Delay function replaces WaitForSeconds
            delay(2000) // 2 seconds in milliseconds
            
            // Custom suspend function for complex waiting
            waitUntil { canSpawnEnemy() }
            
            // Spawn enemy (this would interface with your game engine)
            spawnEnemy(spawnPoint)
            
            // Yield to other coroutines (similar to yield return null)
            yield()
        }
    }
    
    private suspend fun waitUntil(condition: () -> Boolean) {
        while (!condition()) {
            delay(16) // ~60 FPS check rate
        }
    }
    
    private fun canSpawnEnemy(): Boolean {
        return getCurrentEnemyCount() < 5
    }
}

Key Takeaway: Kotlin coroutines are more powerful and flexible than Unity coroutines, but the concept of cooperative multitasking is similar.

Difference 4: Component System vs Class Composition

Unity C# Approach:

// Unity - Component-based architecture with MonoBehaviour
public class Enemy : MonoBehaviour {
    [SerializeField] private float health = 100f;
    [SerializeField] private float speed = 5f;
    
    private Rigidbody rb;
    private AudioSource audioSource;
    
    private void Awake() {
        rb = GetComponent<Rigidbody>();
        audioSource = GetComponent<AudioSource>();
    }
    
    private void Update() {
        MoveTowardsPlayer();
    }
    
    private void MoveTowardsPlayer() {
        var player = GameObject.FindWithTag("Player");
        if (player != null) {
            var direction = (player.transform.position - transform.position).normalized;
            rb.velocity = direction * speed;
        }
    }
    
    public void TakeDamage(float damage) {
        health -= damage;
        audioSource.PlayOneShot(hurtSound);
        
        if (health <= 0) {
            Die();
        }
    }
    
    private void Die() {
        Destroy(gameObject);
    }
}

Kotlin Approach:

// Kotlin - Composition over inheritance with interfaces
interface Movable {
    fun moveTo(target: Vector3)
}

interface Damageable {
    var health: Float
    fun takeDamage(damage: Float)
    fun die()
}

interface AudioCapable {
    fun playSound(soundId: String)
}

// Compose behaviors using delegation
class Enemy(
    private val movement: Movable,
    private val audio: AudioCapable,
    initialHealth: Float = 100f
) : Damageable {
    
    override var health: Float = initialHealth
        private set
    
    private var speed: Float = 5f
    var isAlive: Boolean = true
        private set
    
    fun update(playerPosition: Vector3) {
        if (isAlive) {
            movement.moveTo(playerPosition)
        }
    }
    
    override fun takeDamage(damage: Float) {
        if (!isAlive) return
        
        health -= damage
        audio.playSound("hurt")
        
        if (health <= 0) {
            die()
        }
    }
    
    override fun die() {
        isAlive = false
        audio.playSound("death")
        // Handle death logic
    }
}

// Concrete implementations
class BasicMovement : Movable {
    override fun moveTo(target: Vector3) {
        // Implement movement logic
    }
}

class AndroidAudioPlayer : AudioCapable {
    override fun playSound(soundId: String) {
        // Use Android MediaPlayer or SoundPool
    }
}

// Usage
fun createEnemy(): Enemy {
    return Enemy(
        movement = BasicMovement(),
        audio = AndroidAudioPlayer(),
        initialHealth = 100f
    )
}

Key Takeaway: Kotlin favors composition and interfaces over Unity’s component inheritance model. This leads to more testable and flexible code.

Difference 5: Lifecycle Management - From Unity Events to Android Lifecycle

Unity C# Approach:

// Unity - Automatic lifecycle methods
public class GameManager : MonoBehaviour {
    private PlayerData playerData;
    private AudioManager audioManager;
    
    private void Awake() {
        // Initialize before any Start() calls
        playerData = new PlayerData();
        audioManager = FindObjectOfType<AudioManager>();
    }
    
    private void Start() {
        // Initialize after all Awake() calls
        LoadPlayerData();
        audioManager.PlayBackgroundMusic();
    }
    
    private void OnApplicationPause(bool pauseStatus) {
        if (pauseStatus) {
            SavePlayerData();
            audioManager.PauseAll();
        } else {
            audioManager.ResumeAll();
        }
    }
    
    private void OnApplicationFocus(bool hasFocus) {
        if (!hasFocus) {
            Time.timeScale = 0f; // Pause game
        } else {
            Time.timeScale = 1f; // Resume game
        }
    }
    
    private void OnDestroy() {
        SavePlayerData();
    }
}

Kotlin Approach:

// Kotlin - Manual lifecycle management with Android components
class GameActivity : AppCompatActivity() {
    private lateinit var playerData: PlayerData
    private lateinit var audioManager: AudioManager
    private var gameTimer: Timer? = null
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_game)
        
        // Initialize components (like Unity's Awake)
        playerData = PlayerData()
        audioManager = AudioManager(this)
        
        // Start game logic (like Unity's Start)
        loadPlayerData()
        audioManager.playBackgroundMusic()
        startGameTimer()
    }
    
    override fun onPause() {
        super.onPause()
        // App is going to background (like OnApplicationPause(true))
        savePlayerData()
        audioManager.pauseAll()
        gameTimer?.pause()
    }
    
    override fun onResume() {
        super.onResume()
        // App is coming back to foreground (like OnApplicationPause(false))
        audioManager.resumeAll()
        gameTimer?.resume()
    }
    
    override fun onDestroy() {
        super.onDestroy()
        // Cleanup (like Unity's OnDestroy)
        savePlayerData()
        audioManager.release()
        gameTimer?.cancel()
    }
    
    private fun startGameTimer() {
        gameTimer = Timer().apply {
            scheduleAtFixedRate(object : TimerTask() {
                override fun run() {
                    // Game update loop (like Unity's Update, but manual)
                    updateGame()
                }
            }, 0, 16) // ~60 FPS
        }
    }
    
    private fun updateGame() {
        // Your game logic here
    }
}

// Extension for Timer pause/resume functionality
fun Timer.pause() {
    // Implementation depends on your needs
}

fun Timer.resume() {
    // Implementation depends on your needs
}

Key Takeaway: Unlike Unity’s automatic lifecycle callbacks, Android requires explicit lifecycle management. You must manually handle app states and resource cleanup. This connects to proper state management patterns, which become even more important when building Compose UI applications with proper @Composable annotations.

Making the Transition: Practical Tips

1. Start with Data Classes

Unity developers are used to [System.Serializable] classes. Kotlin’s data classes are similar but more powerful:

// Kotlin data class (like Unity's serializable class)
data class PlayerStats(
    val name: String,
    val level: Int,
    val experience: Int,
    val health: Float = 100f
) {
    // Automatically generates: equals(), hashCode(), toString(), copy()
    
    val nextLevelXP: Int
        get() = level * 1000
}

// Usage - much cleaner than Unity's approach
val player = PlayerStats("Hero", 5, 4500)
val leveledUpPlayer = player.copy(level = 6, experience = 0)

2. Replace Unity’s FindObjectOfType with Dependency Injection

// Instead of FindObjectOfType, use constructor injection
class GameManager(
    private val audioManager: AudioManager,
    private val playerRepository: PlayerRepository
) {
    fun startGame() {
        audioManager.playBackgroundMusic()
        val playerData = playerRepository.loadPlayer()
        // Game logic
    }
}

3. Use Kotlin’s Built-in Collections

// Rich collection operations (like LINQ in C#)
val activeEnemies = enemies
    .filter { it.isAlive }
    .sortedBy { it.distanceToPlayer }
    .take(10)

val totalDamage = weapons
    .filter { it.isEquipped }
    .sumOf { it.damage }

When to Use Unity vs Kotlin

Choose Unity When:

• Building games or interactive 3D/2D content
• Need cross-platform deployment (mobile, desktop, console)
• Working with AR/VR experiences
• Want visual scripting and scene-based development

Choose Kotlin When:

• Building native Android applications
• Need maximum performance on Android
• Integrating deeply with Android system features
• Building business/productivity apps
• Want to share code between Android and iOS (Kotlin Multiplatform)

Use Both When:

• Creating companion apps for Unity games
• Building AR apps that need native mobile integration
• Offering full mobile development services to clients
• Developing game analytics or backend services

Conclusion

The transition from Unity C# to Kotlin is smoother than you might expect. Your object-oriented programming skills, understanding of mobile constraints, and experience with component-based architecture all transfer well.

The key differences—null safety, property syntax, coroutines, composition patterns, and lifecycle management—become second nature with practice. Many Unity developers find that learning Kotlin actually makes them better C# developers too, as both languages continue to influence each other.

Start small: build a simple Android app using the concepts I’ve outlined, then gradually expand your Kotlin skills. Focus on mastering the fundamentals like proper Compose annotations before tackling complex state management. Before long, you’ll be offering both game development and native mobile app services to your clients.

Ready to expand your mobile development skills? Contact Angry Shark Studio for expert guidance on Unity and Kotlin development, or explore our mobile portfolio to see how we’ve successfully combined both technologies for client projects.

Related Reading:

• Kotlin Beginner Mistake: Using !! Everywhere for Null Safety
• Compose Beginner Mistake: Forgetting @Composable Annotations
• Unity Mobile Performance: Memory Management Tips for AR/VR