How to build a BagComponent with ECS

Unity Engine
,
1

As the header, I wanna write a BagComponent which contains a list of Entities and some common properties like CurrentWeight,MaxWeight,CurrentCount,MaxCount etc.(With pure ECS)

2

Dynamic buffers should be helpful.

using Unity.Entities;

public struct Bag : IComponentData
{
    public int CurrentWeight;
    public int MaxWeight;
    public int CurrentCount;
    public int MaxCount;
}

using Unity.Entities;

[InternalBufferCapacity(16)]
public struct BagBufferElement : IBufferElementData
{
    public Entity Entity;

    public static implicit operator Entity(BagBufferElement e) => e.Entity;
    public static implicit operator BagBufferElement(Entity e) => new BagBufferElement { Entity = e };
}

var bag = EntityManager.CreateEntity(typeof(Bag));
EntityManager.AddBuffer<BagBufferElement>(bag);
3

Wow, thank you so much!

4

And is there anyway to store the buffer and common properties in a single component?

5

Not at the moment. What you can do is prepare an Entity that has the DynamicBuffer then use this entity as reference to the owner component. For example:

// This is the bag entity
Entity bag = EntityManager.CreateEntity(typeof(Bag));
EntityManager.AddBuffer<BagBufferElement>(bag);

// This is the owner component
struct Character : IComponentData {
    public Entity bagEntity;
}

Entity characterEntity = EntityManager.CreateEntity(typeof(Character));

// Prepare the component
Character character = new Character() {
    bagEntity = bag
};

EntityManager.SetComponentData(characterEntity, character);