编辑器下的一些操作默认是不可撤销的，如创建、销毁物体，使用Undo可以将某个操作标记为可撤销操作，Ctrl+Z即可撤销

官方文档

 实例：

using UnityEngine;
using UnityEditor;

public class TestUndoEditorWindow
{

    [InitializeOnLoadMethod]
    public static void Init()
    {
        SceneView.duringSceneGui += DuringSceneGui;
    }

    private static void DuringSceneGui(SceneView sceneView)
    {
        Handles.BeginGUI();
        if(GUI.Button(new Rect(0,10,100,20),"创建单个Cube"))
        {
            //手动对可撤销操作分组
            Undo.IncrementCurrentGroup();
            //创建Cube
            GameObject cube = GameObject.CreatePrimitive(PrimitiveType.Cube);

            //销毁Cube
            //Undo.DestroyObjectImmediate(cube);
            //标记可撤销操作
            Undo.RegisterCreatedObjectUndo(cube,"创建单个Cube : " + cube.name);
        }
        if(GUI.Button(new Rect(0,35,100,20),"创建多个Cube"))
        {
            Undo.IncrementCurrentGroup();

            for(int i = 0; i < 5; i++)
            {
                GameObject cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
                cube.transform.position = new Vector3(i * 1.5f,0,0);
                Undo.RegisterCreatedObjectUndo(cube,"创建多个Cube : " + cube.name);
            }
        }
        Handles.EndGUI();
    }

}