ソースコード

#if UNITY_EDITOR

using System;
using UnityEditor;
using UnityEngine;

namespace Kogane
{
    [InitializeOnLoad]
    public static class ScreenSizeChecker
    {
        public static event Action OnChanged;

        static ScreenSizeChecker()
        {
            var oldWidth  = Screen.width;
            var oldHeight = Screen.height;

            EditorApplication.update += () =>
            {
                var newWidth  = Screen.width;
                var newHeight = Screen.height;

                if ( oldWidth != newWidth || oldHeight != newHeight )
                {
                    OnChanged?.Invoke();
                }

                oldWidth  = newWidth;
                oldHeight = newHeight;
            };
        }
    }
}

#endif