open-project-1/UOP1_Project/Assets/Scripts/StateMachine/Editor/Utilities/InitOnlyAttributeDrawer.cs

using UnityEditor;
using UnityEngine;

namespace UOP1.StateMachine.Editor
{
	[CustomPropertyDrawer(typeof(InitOnlyAttribute))]
	public class InitOnlyAttributeDrawer : PropertyDrawer
	{
		private static readonly string _text = "Changes to this parameter during Play mode won't be reflected on existing StateMachines";
		private static readonly GUIStyle _style = new GUIStyle(GUI.skin.GetStyle("helpbox")) { padding = new RectOffset(5, 5, 5, 5) };

		public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
		{
			if (EditorApplication.isPlaying)
			{
				position.height = _style.CalcHeight(new GUIContent(_text), EditorGUIUtility.currentViewWidth);
				EditorGUI.HelpBox(position, _text, MessageType.Info);
				position.y += position.height + EditorGUIUtility.standardVerticalSpacing;
				position.height = EditorGUI.GetPropertyHeight(property, label);
			}

			EditorGUI.PropertyField(position, property, label);
		}

		public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
		{
			float height = EditorGUI.GetPropertyHeight(property, label);

			if (EditorApplication.isPlaying)
			{
				height += _style.CalcHeight(new GUIContent(_text), EditorGUIUtility.currentViewWidth)
					+ EditorGUIUtility.standardVerticalSpacing * 4;
			}

			return height;
		}
	}
}