A mini-script to simplify the work of designers in a project on Unity.

DesignMode.cs

using System.Runtime.CompilerServices;
using UnityEngine;

namespace DCFApixels
{
    public static class DesignMode
    {
        internal static bool _isOn = false;
        public static bool ON
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get { return _isOn; }
        }
        public static bool OFF
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get { return !_isOn; }
        }
    }
    [System.AttributeUsage(System.AttributeTargets.All, Inherited = false, AllowMultiple = false)]
    public sealed class DesignOnlyAttribute : PropertyAttribute
    {
        public DesignOnlyAttribute()
        {
            order = int.MinValue;
        }
    }
    [System.AttributeUsage(System.AttributeTargets.All, Inherited = false, AllowMultiple = false)]
    public sealed class DevelopmentOnlyAttribute : PropertyAttribute
    {
        public DevelopmentOnlyAttribute()
        {
            order = int.MinValue;
        }
    }
}


#if UNITY_EDITOR
namespace DCFApixels.Editors
{
    using UnityEditor;
    [InitializeOnLoad]
    internal static class DesignModeSwitcher
    {
        private const string _PREF_KEY_NAME = "DCFApixels_DesignMode_IsOn";
        static DesignModeSwitcher()
        {
            int x = PlayerPrefs.GetInt(_PREF_KEY_NAME);
            DesignMode._isOn = x > 0;
        }
        [MenuItem("Design Mode/Toggle")]
        public static void ToggleDesignMode()
        {
            DesignMode._isOn = !DesignMode._isOn;
            PlayerPrefs.SetInt(_PREF_KEY_NAME, DesignMode._isOn ? 1 : 0);
        }
    }
    [CustomPropertyDrawer(typeof(DesignOnlyAttribute), true)]
    internal class DesignOnlyAttributeDrawer : ViewModeDrawer<DesignOnlyAttribute> { }
    [CustomPropertyDrawer(typeof(DevelopmentOnlyAttribute), true)]
    internal class DevelopmentOnlyAttributeDrawer : ViewModeDrawer<DevelopmentOnlyAttribute> { }
    internal class ViewModeDrawer<T> : PropertyDrawer
    {
        protected static bool _isDesignOnly = typeof(T) == typeof(DesignOnlyAttribute);
        private static bool IsDraw
        {
            get { return _isDesignOnly ? DesignMode.ON : DesignMode.OFF; }
        }
        public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
        {
            if (IsDraw)
            {
                return EditorGUI.GetPropertyHeight(property, label);
            }
            return 0f;
        }
        public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
        {
            if (IsDraw)
            {
                EditorGUI.PropertyField(position, property, label, true);
            }
        }
    }
}
#endif

DesignMode.md

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The script adds a mode switcher for designers and for developers in a panel at the top of the Unity window called Design Mode.

Through the DesignMode.ON property, you can get the bool value of whether design mode is enabled.

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And also adds 2 attributes to customize the display of types in the inspector::

public class SomeMonoBehaviour : MonoBehaviour
{
    // The field is visible only in Design Mode.
    [DesignOnly] public int someField1;
    // Hides the field in Design Mode.
    [DevelopmentOnly] public int someField2;
}

DesignMode.ON == false

DesignMode.ON == true

---

To get the current value of DesignMode.ON without depending on this script, you can get it like this:

bool isDesignMode = PlayerPrefs.GetInt("DCFApixels_DesignMode_IsOn") == 0 ? false : true;