Customizing the inspector for your game objects

using System;
using UnityEngine;

public class ShowInspector : MonoBehaviour
{
    [Range(1, 10)]
    public float Price = 5;

    public ExtraData ExtraData = new ExtraData();
    public UsableItems UsableItems = UsableItems.None;

    public void ResetValues()
    {
        UsableItems = UsableItems.None;
        Price = 5;
    }
}

[Serializable]
public class ExtraData
{
    public bool ShowIcon = true;

    [Range(32.0f, 256)]
    public float IconSize = 96;

}

using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

[CustomEditor(typeof(ShowInspector)), CanEditMultipleObjects]
public class ShowInspector_UI : Editor
{
    private ShowInspector _showInspector;
    private string _oldName;
    private Texture2D _showItem = null;

    private static Texture2D GetTexture(string name)
    {
        try
        {
            Texture2D go = (Texture2D)Resources.Load(name);
            return go;
        }
        catch
        {
            return null;
        }
    }


    public override void OnInspectorGUI()
    {
        DrawDefaultInspector();

        if (_showInspector.ExtraData.ShowIcon)
        {
            if (_showItem == null ||
            _oldName != _showInspector.UsableItems.ToString())
            {
                _showItem = GetTexture(_showInspector.UsableItems.ToString());
                _oldName = _showInspector.UsableItems.ToString();
            }

            if (_showItem != null)
            {
                GUILayout.Label(
                    _showItem,
                    GUILayout.Width(_showInspector.ExtraData.IconSize),
                    GUILayout.Height(_showInspector.ExtraData.IconSize));
            }
        }

        if (_showInspector.UsableItems != UsableItems.None)
        {
            GUI.color = Color.green;
            if (GUILayout.Button("Reset Values"))
            {
                _showInspector.ResetValues();
            }
        }

    }

    private void OnEnable()
    {
        _showInspector = (ShowInspector)target;
    }
}