Unity Rendering Sorting Layer

SortComponent.cs

using UnityEngine;
using System.Collections;

namespace SortingOrder
{
    [RequireComponent(typeof(Renderer))]
    public class SortComponent : MonoBehaviour { }
}

SortingOrderEditor.cs

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

namespace SortingOrder
{
    [CustomEditor(typeof(SortComponent), true)]
    public class SortingOrderEditor : Editor
    {
        private string[] GetSortingLayerNames()
        {
            var internalEditorUtilityType = typeof(InternalEditorUtility);
            PropertyInfo sortingLayersProperty = internalEditorUtilityType.GetProperty("sortingLayerNames", BindingFlags.Static | BindingFlags.NonPublic);
            return (string[])sortingLayersProperty.GetValue(null, new object[0]);
        }

        private int GetSelectedID(string[] layerNames, Renderer renderer)
        {
            string currentLayer = renderer.sortingLayerName;
            for (int index = 0; index < layerNames.Length; index++)
            {
                if (layerNames[index] == currentLayer)
                {
                    return index;
                }
            }
            return -1;
        }

        public override void OnInspectorGUI()
        {
            base.OnInspectorGUI();
            Renderer renderer = ((SortComponent)target).renderer;
            string[] layerNames = GetSortingLayerNames();
            EditorGUILayout.LabelField("Sorting Layer", EditorStyles.boldLabel);
            EditorGUI.indentLevel++;
            EditorGUILayout.LabelField("Current Layer ID: ", renderer.sortingLayerID.ToString());
            EditorGUILayout.BeginHorizontal();
            EditorGUI.BeginChangeCheck();
            int selected = EditorGUILayout.Popup("Layer Name:", GetSelectedID(layerNames, renderer), layerNames);
            if (EditorGUI.EndChangeCheck())
            {
                renderer.sortingLayerName = layerNames[selected];
            }
            EditorGUILayout.EndHorizontal();
            EditorGUILayout.BeginHorizontal();
            EditorGUI.BeginChangeCheck();
            int order = EditorGUILayout.IntField("Sorting Order: ", renderer.sortingOrder);
            if (EditorGUI.EndChangeCheck())
            {
                if (order < 0)
                {
                    order = 0;
                }
                renderer.sortingOrder = order;
            }
            EditorGUILayout.EndHorizontal();
        }
    }
}