I'm trying to implement an observable pattern on variables, so that I can hook up UI components, etc. to change displayed values or other actions when their value changes.
I wanted three features that the built-in Delegate system doesn't satisfy:
- (optional) try/catch calls so that some not important UI element doesn't break the whole game loop
- having the variables in ScriptableObjects for easy storage and inspection
- having a list of listeners in the inspector for debugging and transparency
Here is the code I finally came up with, and it does what I need. But I'm relatively new to C# so I'm looking forward to improvements and advise:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Events;
using UnityEditor;
using Sirenix.OdinInspector;
[CreateAssetMenu(fileName = "New Observable Float", menuName = "Observables/Float")]
public class ObservableFloat : ScriptableObject {
[System.Serializable]
public class Listener {
[DisplayAsString, HideInInspector] public int ID;
[DisplayAsString, HideLabel, HorizontalGroup] public string Observer;
[DisplayAsString, HideLabel, HorizontalGroup] public string Method;
[HideInInspector] public UnityAction<float> Callback;
public Listener(UnityAction<float> cb) {
ID = cb.GetHashCode();
Observer = cb.Target.ToString();
Method = cb.Method.ToString();
Callback = cb;
}
}
[Delayed]
[OnValueChanged("NotifyListeners")]
[SerializeField] private float m_Value;
public float Value {
get {
return m_Value;
}
set {
m_Value = value;
NotifyListeners();
}
}
[Tooltip("Log Invoke() calls")]
[SerializeField] bool Trace;
[Tooltip("Use try/catch around Invoke() calls so events continue to other listeners even if one fails")]
[SerializeField] bool CatchExceptions;
[ListDrawerSettings(DraggableItems = false, Expanded = true, ShowIndexLabels = false, ShowPaging = false, ShowItemCount = true)]
[SerializeField] List<Listener> listeners = new List<Listener>();
void Awake() {
// clear out whenever we start - just in case some observer doesn't properly remove himself
// maybe later I'll also add persistent listeners, but for now I don't see the use case
listeners = new List<Listener>();
}
void NotifyListeners() {
foreach (Listener listener in listeners) {
if (Trace) {
Debug.Log("invoking "+listener.Observer+" / "+listener.Method+ " / value = "+m_Value);
}
if (CatchExceptions) {
try {
listener.Callback.Invoke(m_Value);
} catch (System.Exception exception) {
Debug.LogException(exception, this);
}
} else {
listener.Callback.Invoke(m_Value);
}
}
}
public void AddListener(UnityAction<float> func) { listeners.Add(new Listener(func)); }
public void RemoveListener(UnityAction<float> func) { listeners.RemoveAll(l => l.ID == func.GetHashCode()); }
}
Note that I'm using a few OdinInspector tags to make the inspector display a bit more beautiful, but it's not required for functionality.
Note 2: Yes, I plan to turn this into a generic eventually.