Unity Development

Unity Development Guide

A comprehensive guide for Unity development. This skill serves as always-referenced parent skill, providing common patterns and tool selection guidance.

Architecture Patterns

Fail-Fast Principle

Do not write null checks. Use objects directly when their existence is assumed.

// NG: Forbidden pattern
if (component != null) { component.DoSomething(); }
if (gameObject != null) { gameObject.SetActive(false); }
if (service != null) { service.Execute(); }

// OK: Correct pattern - direct usage
GetComponent<Rigidbody>().velocity = Vector3.zero;
GameService.Initialize();
target.position = Vector3.zero;

Applies to:

• Null check after GetComponent<T>()
• Null check after Find*()
• Null check after [Inject]

No GetComponent in Update

GetComponent every frame causes GC allocation and performance degradation. Cache in Awake.

// NG: GC allocation every frame
void Update()
{
    GetComponent<Rigidbody>().velocity = input;
}

// OK: Cache in Awake
private Rigidbody _rb;

void Awake()
{
    _rb = GetComponent<Rigidbody>();
}

void Update()
{
    _rb.velocity = input;
}

UniTask Patterns

Use UniTask instead of coroutines. async void is forbidden.

using Cysharp.Threading.Tasks;

// NG: async void
async void Start()
{
    await DoWorkAsync();
}

// OK: UniTaskVoid + destroyCancellationToken
async UniTaskVoid Start()
{
    await DoWorkAsync(destroyCancellationToken);
}

// OK: When return value is needed
async UniTask<int> CalculateAsync(CancellationToken ct)
{
    await UniTask.Delay(1000, cancellationToken: ct);
    return 42;
}

Best Practices:

• Use destroyCancellationToken for auto-cancel on GameObject destruction
• UniTask.Delay > Task.Delay (zero allocation)
• UniTask.WhenAll for parallel execution

VContainer DI

Use VContainer for dependency injection. Constructor injection recommended.

// Interface definition
public interface IPlayerService
{
    void Initialize();
}

// Implementation class
public class PlayerService : IPlayerService
{
    public void Initialize() { /* ... */ }
}

// Consumer (MonoBehaviour)
public class GameManager : MonoBehaviour
{
    [Inject] private readonly IPlayerService _playerService;

    void Start()
    {
        _playerService.Initialize();
    }
}

// LifetimeScope configuration
public class GameLifetimeScope : LifetimeScope
{
    protected override void Configure(IContainerBuilder builder)
    {
        builder.Register<IPlayerService, PlayerService>(Lifetime.Singleton);
        builder.RegisterComponentInHierarchy<GameManager>();
    }
}

Lifetime Selection:

• Lifetime.Singleton - One instance for entire app
• Lifetime.Scoped - One instance per scene
• Lifetime.Transient - New instance each time

MCP Tool Categories

C# Code Editing

Scene & GameObject

Asset Management

PlayMode & Testing

UI Systems

Composite Workflow Examples

Example 1: Scene Transition with UI Button

Required operations: UI creation + Scene management + C# script

// 1. Create button GameObject
mcp__unity-mcp-server__create_gameobject({
  name: "StartButton",
  parentPath: "/Canvas"
})

// 2. Add Button component
mcp__unity-mcp-server__add_component({
  gameObjectPath: "/Canvas/StartButton",
  componentType: "Button"
})

// 3. Create click handler script
mcp__unity-mcp-server__create_class({
  path: "Assets/Scripts/UI/StartButtonHandler.cs",
  className: "StartButtonHandler",
  baseType: "MonoBehaviour",
  namespace: "Game.UI"
})

// 4. Add OnClick implementation
mcp__unity-mcp-server__edit_structured({
  path: "Assets/Scripts/UI/StartButtonHandler.cs",
  symbolName: "StartButtonHandler",
  operation: "insert_after",
  newText: `
    public void OnStartClicked()
    {
        SceneManager.LoadScene("GameScene");
    }
`
})

Example 2: Create Enemy Character

Required operations: GameObject + Components + C# script + Prefab

// 1. Create enemy GameObject
mcp__unity-mcp-server__create_gameobject({
  name: "Enemy",
  primitiveType: "capsule",
  position: { x: 0, y: 1, z: 0 }
})

// 2. Add components
mcp__unity-mcp-server__add_component({
  gameObjectPath: "/Enemy",
  componentType: "Rigidbody"
})

// 3. Create enemy script
mcp__unity-mcp-server__create_class({
  path: "Assets/Scripts/Enemies/EnemyController.cs",
  className: "EnemyController",
  baseType: "MonoBehaviour"
})

// 4. Add AI implementation
mcp__unity-mcp-server__edit_structured({
  path: "Assets/Scripts/Enemies/EnemyController.cs",
  symbolName: "EnemyController",
  operation: "insert_after",
  newText: `
    [SerializeField] private float _speed = 3f;
    private Transform _target;

    void Update()
    {
        if (_target != null)
            transform.position = Vector3.MoveTowards(
                transform.position,
                _target.position,
                _speed * Time.deltaTime
            );
    }
`
})

// 5. Convert to prefab
mcp__unity-mcp-server__create_prefab({
  gameObjectPath: "/Enemy",
  prefabPath: "Assets/Prefabs/Enemies/Enemy.prefab"
})

Example 3: PlayMode Testing

Required operations: Test creation + PlayMode control + Input simulation

// 1. Create test class
mcp__unity-mcp-server__create_class({
  path: "Assets/Tests/PlayMode/PlayerMovementTests.cs",
  className: "PlayerMovementTests",
  namespace: "Tests.PlayMode",
  usings: "NUnit.Framework,UnityEngine.TestTools,System.Collections"
})

// 2. Add PlayMode test implementation
mcp__unity-mcp-server__edit_structured({
  path: "Assets/Tests/PlayMode/PlayerMovementTests.cs",
  symbolName: "PlayerMovementTests",
  operation: "insert_after",
  newText: `
    [UnityTest]
    public IEnumerator Player_MovesForward_WhenWPressed()
    {
        var player = Object.FindObjectOfType<PlayerController>();
        var startPos = player.transform.position;

        yield return null;

        // Simulate W key input
        // Use input_keyboard tool during test execution

        yield return new WaitForSeconds(0.5f);

        Assert.Greater(player.transform.position.z, startPos.z);
    }
`
})

// 3. Run tests
mcp__unity-mcp-server__run_tests({
  testMode: "PlayMode",
  filter: "PlayerMovementTests"
})

Child Skill Reference

Refer to the following child skills when detailed implementation patterns are needed:

Quick Decision Tree

Unity Development Task
├─ Need code editing?
│   ├─ YES → edit_snippet / edit_structured
│   │         Details: unity-csharp-editing
│   └─ NO → Next
├─ Need scene/GameObject operations?
│   ├─ YES → create_gameobject / add_component
│   │         Details: unity-scene-management
│   └─ NO → Next
├─ Need asset operations?
│   ├─ YES → create_prefab / addressables_manage
│   │         Details: unity-asset-management
│   └─ NO → Next
├─ Need UI implementation?
│   ├─ Game UI → unity-game-ugui-design or unity-game-ui-toolkit-design
│   └─ Editor UI → unity-editor-imgui-design
└─ Need testing/verification?
    └─ YES → play_game / run_tests
              Details: unity-playmode-testing