Entity Component System c#

Question

I'm currently creating a 2D game engine in C#. At the moment, I'm implementing an entity component system.

My structure is as follows:

• Entity Class: Contains a list of IGameComponent's, you can add, remove and delete any component by class type. (ie; entity.RemoveComponent(typeof(Transform));. It also contains a parent Entity, and a list child entities.
• IGameComponent Interface: For now, is just an empty interface. (Note that: Components only contain data, and not functionality)
• Entity Pool: Contains a list of all the active objects in the game, it's also used to create and destroy entities.

Everything so far is great.

However, I'm faced with a problem. Since components only contain data I need a way to initialize, update and render the components and I'd rather not just add a bunch of virtual methods to a GameComponent class, however I don't know of any other way to resolve it.

What are my options?

EDIT:

I've seen that Unity uses methods like 'SendMessage' which I can only assume uses reflection to call methods. Should I implement something similar?

Answer 1

I don't know if you still need it, but I have made something similar a few years ago and it might help you. It's written in C# built on top of MonoGame/XNA

You GameObject class can look like this

public class GameObject
{
    List<GameObjectComponent> _goComponent = new List<GameObjectComponent();

    public T GetComponent<T>() where T : GameObjectComponent
    {
        foreach (GameObjectComponent goc in _goComponent)
            if (goc.GetType().Equals(typeof(T)))
                return (T)goc;
        return null;
    }

    public void AddComponent(GameObjectComponent gameObjectComponent)
    {
        _goComponent.Add(gameObjectComponent);
        gameObjectComponent.gameObject = this;
        gameObjectComponent.Init();
    }

    public virtual void Update(GameTime gameTime)
    {
        foreach (GameObjectComponent _goc in _goComponent)
            _goc.Update(gameTime);
    }

    public static void Instantiate(GameObject gameObject)
    {
       Scene._AddedGO.Add(gameObject);
    }

    public static void Destroy(GameObject gameObject)
    {
       Scene._RemoveGO.Add(gameObject);
    }

}

GameObjectComponent is similar to MonoBehaivior from Unity3D

  public class GameObjectComponent
{

    public GameObject gameObject;

    public GameObjectComponent()
    {

    }

    public virtual void Init()
    {

    }

    public virtual void Update(GameTime gameTime)
    {

    }
}

and then you Inherit other classes like so:

public class Sprite : GameObjectComponent
{
    public Texture2D texture;
    public Vector2 origin = Vector2.Zero;
    public Rectangle rect;
    public Rectangle sourceRect;
    public Color color = Color.White;
    public float rotation = 0f;
    private float layerDepth = 0f;
    public int scale = 1;

    public Sprite()
    {

    } 

    public void Load(string path)
    {
        texture = Setup.ContentDevice.Load<Texture2D>(path);
    }

}

now you can finally create you Player GameObject

class Player : GameObjectComponent
{
    float speed = 150f;
    KeyboardState keyState;

    float pos_X;
    float pos_Y;
    int rect_X;
    int rect_Y;

    public Player(float x, float y, int rx, int ry)
    {
        pos_X = x;
        pos_Y = y;
        rect_X = rx;
        rect_Y = ry;
    }

    public override void Init()
    {
        Sprite sprite = new Sprite();
        gameObject.AddComponent(sprite);

        gameObject.GetComponent<Sprite>().Load("Sprites/MainGuySpriteSheet_0");
        gameObject.GetComponent<Sprite>().scale = 1;
        gameObject.GetComponent<Sprite>().rect = new Rectangle(46, 0, 32, 36);


        Transform transform = new Transform();
        gameObject.AddComponent(transform);
        //  gameObject.GetComponent<Transform>().position = new Vector2(Screen.width / 2 - gameObject.GetComponent<Sprite>().rect.Width, Screen.height / 2 - gameObject.GetComponent<Sprite>().rect.Height);
        gameObject.GetComponent<Transform>().position = new Vector2(pos_X, pos_Y - 32 * (gameObject.GetComponent<Sprite>().scale - 1));

        RectCollider collider = new RectCollider();
        gameObject.AddComponent(collider);
        gameObject.GetComponent<RectCollider>().Set(gameObject.GetComponent<Sprite>(), gameObject.GetComponent<Transform>());

        SpriteRenderer render = new SpriteRenderer();
        gameObject.AddComponent(render);
        gameObject.GetComponent<SpriteRenderer>().layer = 1;
        gameObject.GetComponent<SpriteRenderer>().Set(gameObject.GetComponent<Sprite>());
    }

    public override void Update(GameTime gameTime)
    {
        //movex = transform.position.X -= 25 * gameTime.DeltaTime();


        if (Keyboard.GetState().IsKeyDown(Keys.Left))
            gameObject.GetComponent<Transform>().Move(-speed * gameTime.DeltaTime(), 0);

       else if (Keyboard.GetState().IsKeyDown(Keys.Right))
            gameObject.GetComponent<Transform>().Move(speed * gameTime.DeltaTime(), 0);

       else if (Keyboard.GetState().IsKeyDown(Keys.Down))
            gameObject.GetComponent<Transform>().Move(0, speed * gameTime.DeltaTime());

       else if (Keyboard.GetState().IsKeyDown(Keys.Up))
            gameObject.GetComponent<Transform>().Move(0, -speed * gameTime.DeltaTime());

        if (Keyboard.GetState().IsKeyDown(Keys.Space) && !keyState.IsKeyDown(Keys.Space))
        {
            GameObject tomato = new GameObject();
            tomato.AddComponent(new Tomato());
            tomato.GetComponent<Transform>().position = gameObject.GetComponent<Transform>().position;
            GameObject.Instantiate(tomato);
        }

        if (Keyboard.GetState().IsKeyDown(Keys.Q) && !keyState.IsKeyDown(Keys.Q))
        {
            SceneManager.LoadScene(new AnotherOne());
        }

        keyState = Keyboard.GetState();


        gameObject.GetComponent<Transform>().position.Y = MathHelper.Clamp(gameObject.GetComponent<Transform>().position.Y, 0, Screen.bounds.Height - gameObject.GetComponent<Sprite>().rect.Height * gameObject.GetComponent<Sprite>().scale);
        gameObject.GetComponent<Transform>().position.X = MathHelper.Clamp(gameObject.GetComponent<Transform>().position.X, 0, Screen.bounds.Width - gameObject.GetComponent<Sprite>().rect.Width * gameObject.GetComponent<Sprite>().scale);
    }

}

I hope it's not too confusing and helps you a little bit. To make it clearer I leave a link to the git here: https://github.com/Memorix101/MonoGame_ComponentSystem

Cheers, Memorix101 :)