An observable list for Unity

ObservedList.cs

public abstract class ObservedList { }

[Serializable]
public class ObservedList<T> : ObservedList, IList<T>
{
    public delegate void ChangedDelegate(int index, T oldValue, T newValue);

    // In a bit of a dirty hack the editor scripts is looking for this field
    // with exactly this name "_list"
    [SerializeField] private List<T> _list = new List<T>();

    // NOTE: I changed the signature to provide a bit more information
    // now it returns index, oldValue, newValue
    public event ChangedDelegate Changed;

    public event Action Updated;

    public IEnumerator<T> GetEnumerator()
    {
        return _list.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    public void Add(T item)
    {
        _list.Add(item);
        Updated?.Invoke();
    }

    public void Clear()
    {
        _list.Clear();
        Updated?.Invoke();
    }

    public bool Contains(T item)
    {
        return _list.Contains(item);
    }

    public void CopyTo(T[] array, int arrayIndex)
    {
        _list.CopyTo(array, arrayIndex);
    }

    public bool Remove(T item)
    {
        var output = _list.Remove(item);
        Updated?.Invoke();

        return output;
    }

    public int Count => _list.Count;
    public bool IsReadOnly => false;

    public int IndexOf(T item)
    {
        return _list.IndexOf(item);
    }

    public void InsertRange(int index, IEnumerable<T> collection)
    {
        _list.InsertRange(index, collection);
        Updated?.Invoke();
    }

    public void AddRange(IEnumerable<T> collection)
    {
        _list.AddRange(collection);
        Updated?.Invoke();
    }

    public void RemoveAll(Predicate<T> predicate)
    {
        _list.RemoveAll(predicate);
        Updated?.Invoke();
    }

    public void RemoveRange(int index, int count)
    {
        _list.RemoveRange(index, count);
        Updated?.Invoke();
    }

    public void Insert(int index, T item)
    {
        _list.Insert(index, item);
        Updated?.Invoke();
    }

    public void RemoveAt(int index)
    {
        _list.RemoveAt(index);
        Updated?.Invoke();
    }

    public T this[int index]
    {
        get { return _list[index]; }
        set
        {
            var oldValue = _list[index];
            _list[index] = value;
            Changed?.Invoke(index, oldValue, value);

            // I would also call the generic one here
            Updated?.Invoke();
        }
    }
}

ObservedListDrawer.cs

[CustomPropertyDrawer(typeof(ObservedList), true)]
public class ObservedListDrawer : PropertyDrawer
{
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        var list = property.FindPropertyRelative("_list");
        EditorGUI.PropertyField(position, list, label, true);
    }

    public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
    {
        var list = property.FindPropertyRelative("_list");

        return EditorGUI.GetPropertyHeight(list, label, true);
    }
}

I get an error in unity 2022:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.PropertyHandler.GetHeight (UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren) (at <7d481861b3d34328a9633ade22dcedd6>:0)

I think the hack "_list" return null:
var list = property.FindPropertyRelative("_list");

Where shoud I search to find the new way to get the "list" name ?

I get an error in unity 2022: NullReferenceException: Object reference not set to an instance of an object UnityEditor.PropertyHandler.GetHeight (UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren) (at <7d481861b3d34328a9633ade22dcedd6>:0)

I think the hack "_list" return null: var list = property.FindPropertyRelative("_list");

Where shoud I search to find the new way to get the "list" name ?

Hey there, tbh I don't remember why I did this here ^^

The issue here is that the custom editor is only for the base type ObservableList which doesn't have any serialized property called _list (which btw is not a hack but the normal way of accessing those) - only the generic implementation ObservableList<T> has this.

As said I don't really remember and not sure if serialization / editor rules maybe changed since then.

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Though I just tested and imported both into Unity 2021.3.8f1 (Latest LTS) and it works exactly as expected .. maybe stick to the LTS until the pre-release sorts out its bugs ;)