ComponentTitlebarGUI.cs

using System;
using System.Collections.Generic;
using System.Reflection;
using Unity.Profiling;
using UnityEngine;
using UnityEngine.UIElements;
using Object = UnityEngine.Object;

namespace UnityEditor.Custom
{
	public static class ComponentTitlebarGUI
	{
		public static Action<Rect, Object> OnTitlebarGUI;

#if UNITY_EDITOR
		private static ProfilerMarker _profileMarker = new ProfilerMarker($"{nameof(ComponentTitlebarGUI)}.{nameof(OnUpdate)}");
		private static ProfilerMarker _profileMarker2 = new ProfilerMarker($"{nameof(ComponentTitlebarGUI)}.OnTitlebarGUI");
		private static Type type = typeof(EditorWindow).Assembly.GetType("UnityEditor.InspectorWindow");
		private static Type type2 = typeof(EditorWindow).Assembly.GetType("UnityEditor.PropertyEditor");
		private static Type type3 = typeof(EditorWindow).Assembly.GetType("UnityEditor.UIElements.EditorElement");
		private static FieldInfo field = type2.GetField("m_EditorsElement", BindingFlags.NonPublic | BindingFlags.Instance);
		private static FieldInfo field2 = type3.GetField("m_Header", BindingFlags.NonPublic | BindingFlags.Instance);
		private static FieldInfo field3 = type3.GetField("m_EditorTarget", BindingFlags.NonPublic | BindingFlags.Instance);
		private static VisualElement m_EditorsElement;
		private static VisualElement editorsElement => m_EditorsElement ??= GetEditorVisualElement();
		private static Dictionary<VisualElement, Action> _callbacks = new();

		private static VisualElement GetEditorVisualElement()
		{
			EditorWindow window = EditorWindow.GetWindow(type);
			if (window)
			{
				return field.GetValue(window) as VisualElement;
			}

			return null;
		}

		[InitializeOnLoadMethod]
		public static void Init()
		{
			EditorApplication.update -= OnUpdate;
			EditorApplication.update += OnUpdate;
			Selection.selectionChanged -= OnSelectionChanged;
			Selection.selectionChanged += OnSelectionChanged;
		}

		private static void OnSelectionChanged() => _callbacks.Clear();

		private static void OnUpdate()
		{
			using (_profileMarker.Auto())
			{
				VisualElement inspectorRoot = editorsElement;
				if (inspectorRoot == null) return;

				var foundAll = editorsElement.Children();
				foreach (VisualElement element in foundAll)
				{
					if (element.GetType() != type3) continue;

					var localTarget = field3.GetValue(element) as Object;
					if (localTarget)
					{
						IMGUIContainer value2 = field2.GetValue(element) as IMGUIContainer;
						Action callback = null;
						if (_callbacks.TryGetValue(element, out var found))
						{
							callback = found;
						}
						else
						{
							callback = _callbacks[element] = MyLocalCallback;
						}

						if (value2 != null)
						{
							value2.onGUIHandler -= callback;
							value2.onGUIHandler += callback;
						}

						void MyLocalCallback()
						{
							using (_profileMarker2.Auto())
							{
								try
								{
									OnTitlebarGUI?.Invoke(GUILayoutUtility.GetLastRect(), localTarget);
								}
								catch (Exception e)
								{
									Debug.LogException(e);
								}
							}
						}
					}
				}
			}
		}

		//private static GUIContent content = EditorGUIUtility.IconContent("console.erroricon.sml");
		// [InitializeOnLoadMethod]
		// public static void InitTest()
		// {
		// 	ComponentTitlebarGUI.OnTitlebarGUI -= TestGUI;
		// 	ComponentTitlebarGUI.OnTitlebarGUI += TestGUI;
		// }
		//
		// private static void TestGUI(Rect rect, Object target)
		// {
		// 	if (target is not MonoBehaviour) return;
		//
		// 	GUI.Label(rect, content);
		// }
#endif
	}
}