using UnityEngine;
using System;

[AttributeUsage(AttributeTargets.Field)]
public class ListableAttribute : PropertyAttribute
{
    public Type acceptedType;

    public ListableAttribute(Type type)
    {
        acceptedType = type;
    }
}


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using UnityEditor;
using UnityEngine;
using System.Reflection;

[CustomEditor(typeof(TestManager))]
public class TestManagerEditor : Editor
{
    private bool showList = true;

    public override void OnInspectorGUI()
    {
        TestManager tm = (TestManager)target;

        DrawDefaultInspector();

        GUILayout.Space(10);

        showList = EditorGUILayout.Foldout(showList, "Listable Fields");

        if (showList)
        {
            FieldInfo[] fields = typeof(TestManager).GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

            foreach (var field in fields)
            {
                var attr = field.GetCustomAttribute(typeof(ListableAttribute)) as ListableAttribute;

                if (attr != null)
                {
                    if (attr.acceptedType.IsAssignableFrom(field.FieldType))
                    {
                        object value = field.GetValue(tm);
                        object newValue = EditorGUILayout.ObjectField(field.Name, value as UnityEngine.Object, field.FieldType, true);

                        if (newValue != value)
                        {
                            Undo.RecordObject(tm, "Modify Field");
                            field.SetValue(tm, newValue);
                            EditorUtility.SetDirty(tm);
                        }
                    }
                }
            }
        }
    }
}