Unity ScriptableObject, UnityEvent & GenericObject usage

Question

I would like to combine ScriptableObject along with UnityEvent and GenericObject usage. My ultimate goal is to create generic event and listener and then use ScriptableObject to create specific events e.g. GameObject, int and etc. and handle these with respective listeners. Here is the code I have so far: EventTemplate.cs

using System.Collections.Generic;
using UnityEngine;

public class EventTemplate<T> : ScriptableObject {
    private List<ListenerTemplate<T>> listeners = new List<ListenerTemplate<T>>();

    public void Raise(T go) {
        for (int i = listeners.Count - 1; i >= 0; i--) {
            listeners[i].OnEventRaised(go);
        }
    }

    public void RegisterListener(ListenerTemplate<T> listener) {
        listeners.Add(listener);
    }

    public void UnregisterListener(ListenerTemplate<T> listener) {
        listeners.Remove(listener);
    }
}

ListenerTemplate.cs

using UnityEngine;
using UnityEngine.Events;

[System.Serializable]
public class ResponseEvent<T> : UnityEvent<T> { }

public class ListenerTemplate<T> : MonoBehaviour {
    //[SerializeField]
    public EventTemplate<T> gameEvent;

    //[SerializeField]
    public ResponseEvent<T> response;

    private void OnEnable() {
        gameEvent.RegisterListener(this);
    }

    private void OnDisable() {
        gameEvent.UnregisterListener(this);
    }

    public void OnEventRaised(T go) {
        response.Invoke(go);
    }
}

Now, when I have both generic types, I created one Event and one Listener for int type. These are two files:

EventInt.cs

using System.Collections.Generic;
using UnityEngine;

[CreateAssetMenu(fileName = "New Event Template", menuName = "Stage Management/Event Templates/Event Int")]
public class EventInt : EventTemplate<int> {

}

and ListenerInt.cs

using UnityEngine;
using UnityEngine.Events;

[System.Serializable]
public class ResponseInt : ResponseEvent<int> { }

public class ListenerInt : ListenerTemplate<int> {
}

then my expectation was, once I add ListenerInt.cs to specific game component via Editor, I will able to access gameEvent and response in the same fashion I can access them as if I define UnityEvent for int type. However, the reality is that I cannot see / access neither gameEvent nor response via the Editor.

Answer 1

Unity serialization doesn't work on generics T.

you would need to explicitely create an inherited non-generic type for everything you want to serialize in the Inspector. You would need e.g. a

[Serializable] public class IntEvent : UnityEvent<T> { }

in order to be able to serialize it.

---

In order to do what you want (kind of) I would do this:

First use an interface like

public interface IEventListener<in T>
{
    void OnEventRaised(T value);
}

Then make your ListenerTemplate

public abstract class ListenerTemplate<T> : MonoBehaviour, IEventListener<T>
{
    // These have to be provided by the inheritor
    public abstract UnityEvent<T> unityEvent { get; }
    public abstract EventTemplate<T> gameEvent { get; }

    private void OnEnable()
    {
        gameEvent.RegisterListener(this);
    }

    private void OnDisable()
    {
        gameEvent.UnregisterListener(this);
    }

    public void OnEventRaised(T value)
    {
        unityEvent.Invoke(value);
    }
}

As you can see any class inheriting from ListenerTemplate<T> will have to somehow provide both the UnityEvent<T> and the EventTemplate<T>.

So e.g.

// The specific scriptable object doesn't change it just inherits
[CreateAssetMenu(fileName = "New Event Template", menuName = "Stage Management/Event Templates/Event Int")]
public class EventInt : EventTemplate<int>{ }

and

// Specific override for the UnityEvent
[Serializable] public class IntUnityEvent : UnityEvent<int> { }

public class ListenerInt : ListenerTemplate<int>
{
    [SerializeField] private EventInt eventInt;
    [SerializeField] private IntUnityEvent intUnityEvent;

    // override and populate the two abstract properties
    // with the references from the serialized fields
    public override UnityEvent<int> unityEvent => intUnityEvent;
    public override EventTemplate<int> gameEvent => eventInt;
}

This at least reduces the implementation overhead to these two fields for every inheritor and according specific implementations of EventTemplate and UnityEvent.

Finally the EventTemplate<T> just has to use a list of IEventListener instead

public abstract class EventTemplate<TValue> : ScriptableObject
{
    private readonly List<IEventListener<TValue>> listeners = new List<IEventListener<TValue>>();

    public void Raise(TValue go)
    {
        // actually why iterate backwards?
        for (int i = listeners.Count - 1; i >= 0; i--)
        {
            listeners[i].OnEventRaised(go);
        }
    }

    public void RegisterListener(ListenerTemplate<TValue> listener)
    {
        listeners.Add(listener);
    }

    public void UnregisterListener(ListenerTemplate<TValue> listener)
    {
        listeners.Remove(listener);
    }
}