Load a weakly-referenced object at runtime

Unity doesn't automatically load weakly-referenced objects, so it's your responsibility to load them before you need them. To load an object at runtime, you must have a weak reference to the object stored in an ECS component. The weak reference can be either a WeakObjectReference or an UntypedWeakReferenceId. For information on how to store a weak reference to an object, refer to Weakly reference an object.

Load an object at runtime with a WeakObjectReference

The following code example shows how to use WeakObjectReferences to load and render a mesh with a material from an ISystem. For information on how to pass a WeakObjectRefrence to a component, refer to Weakly reference an object from the Inspector.

using Unity.Entities;
using Unity.Entities.Content;
using Unity.Transforms;
using UnityEngine;

public struct WeakObjectReferenceData : IComponentData
{
    public bool startedLoad;
    public WeakObjectReference<Mesh> mesh;
    public WeakObjectReference<Material> material;
}

[WorldSystemFilter(WorldSystemFilterFlags.Default | WorldSystemFilterFlags.Editor)]
[UpdateInGroup(typeof(PresentationSystemGroup))]
public partial struct RenderFromWeakObjectReferenceSystem : ISystem
{
    public void OnCreate(ref SystemState state) { }
    public void OnDestroy(ref SystemState state) { }
    public void OnUpdate(ref SystemState state)
    {
        foreach (var (transform, dec) in SystemAPI.Query<RefRW<LocalToWorld>, RefRW<WeakObjectReferenceData>>())
        {
            if (!dec.ValueRW.startedLoad)
            {
                dec.ValueRW.mesh.LoadAsync();
                dec.ValueRW.material.LoadAsync();
                dec.ValueRW.startedLoad = true;
            }
            if (dec.ValueRW.mesh.LoadingStatus == ObjectLoadingStatus.Completed &&
                dec.ValueRW.material.LoadingStatus == ObjectLoadingStatus.Completed)
            {
                Graphics.DrawMesh(dec.ValueRO.mesh.Result,
                    transform.ValueRO.Value, dec.ValueRO.material.Result, 0);
            }
        }
    }
}

Load an object at runtime with an UntypedWeakReferenceId

The following code example shows how to use the RuntimeContentManager APIs and UntypedWeakReferenceIds to load and render a mesh with a material from an ISystem. For information on how to pass a UntypedWeakReferenceId to a component, refer to Weakly reference an object from a C# script.

using Unity.Entities;
using Unity.Entities.Content;
using Unity.Transforms;
using UnityEngine;
using Unity.Entities.Serialization;

public struct ObjectUntypedWeakReferenceIdData : IComponentData
{
    public bool startedLoad;
    public UntypedWeakReferenceId mesh;
    public UntypedWeakReferenceId material;
}

[WorldSystemFilter(WorldSystemFilterFlags.Default | WorldSystemFilterFlags.Editor)]
[UpdateInGroup(typeof(PresentationSystemGroup))]
public partial struct RenderFromUntypedWeakReferenceIdSystem : ISystem
{
    public void OnCreate(ref SystemState state) { }
    public void OnDestroy(ref SystemState state) { }
    public void OnUpdate(ref SystemState state)
    {
        foreach (var (transform, dec) in SystemAPI.Query<RefRW<LocalToWorld>, RefRW<ObjectUntypedWeakReferenceIdData>>())
        {
            if (!dec.ValueRO.startedLoad)
            {
                RuntimeContentManager.LoadObjectAsync(dec.ValueRO.mesh);
                RuntimeContentManager.LoadObjectAsync(dec.ValueRO.material);
                dec.ValueRW.startedLoad = true;
            }
            if (RuntimeContentManager.GetObjectLoadingStatus(dec.ValueRO.mesh) == ObjectLoadingStatus.Completed &&
                RuntimeContentManager.GetObjectLoadingStatus(dec.ValueRO.material) == ObjectLoadingStatus.Completed)
            {
                Mesh mesh = RuntimeContentManager.GetObjectValue<Mesh>(dec.ValueRO.mesh);
                Material material = RuntimeContentManager.GetObjectValue<Material>(dec.ValueRO.material);
                Graphics.DrawMesh(mesh, transform.ValueRO.Value, material, 0);
            }
        }
    }
}

Additional resources