MoveArrayElementEditor

using UnityEditor;
using UnityEngine;
using Object = UnityEngine.Object;

namespace AlienCore
{
    public static class MoveArrayElementEditor
    {
        [InitializeOnLoadMethod]
        static void Start ()
        {
            // For more information visit: https://docs.unity3d.com/ScriptReference/EditorApplication-contextualPropertyMenu.html
            EditorApplication.contextualPropertyMenu += OnPropertyContextMenu;
        }

        static void OnPropertyContextMenu (GenericMenu menu, SerializedProperty property)
        {
            if (property == null) return;

            // Path of an array is "PropertyName.Array.data[arraylength]", so let's look if the property is an array
            string propertyPath = property.propertyPath;
            if (!propertyPath.Contains (".Array.data[") || !propertyPath.EndsWith ("]")) return;

            // Split the property path and find out the array length
            string[] fullPathSplit = propertyPath.Split ('.');
            string ending = fullPathSplit [fullPathSplit.Length - 1];
            int index = 0;
            if (!int.TryParse (ending.Replace ("data[", "").Replace ("]", ""), out index)) return;

            // Rebuild the path without the ".Array.data[arraylength]" stuff
            string pathToArray = string.Empty;
            for (int i = 0; i < fullPathSplit.Length - 2; i++)
            {
                if (i < fullPathSplit.Length - 3)
                {
                    pathToArray = string.Concat (pathToArray, fullPathSplit [i], ".");
                }
                else
                {
                    pathToArray = string.Concat (pathToArray, fullPathSplit [i]);
                }
            }

            // Get the serialized target object and the property of the array with the path
            Object targetObject = property.serializedObject.targetObject;
            SerializedObject serializedTargetObject = new SerializedObject (targetObject);

            SerializedProperty serializedArray = serializedTargetObject.FindProperty (pathToArray);
            int arrayLength = serializedArray.arraySize;

            if (serializedArray == null) return;

            // Show context menu entry only if the user can move it up or down
            if (index > 0)
            {
                menu.AddItem (new GUIContent ("Move Array Element Down"), false,
                              () => MoveDown (serializedTargetObject, serializedArray, index));
            }

            if (index < arrayLength - 1)
            {
                menu.AddItem (new GUIContent ("Move Array Element Up"), false,
                              () => MoveUp (serializedTargetObject, serializedArray, index));
            }
        }

        static public void MoveDown (SerializedObject target, SerializedProperty array, int index)
        {
            array.MoveArrayElement (index, index - 1);
            target.ApplyModifiedProperties ();
        }

        static public void MoveUp (SerializedObject target, SerializedProperty array, int index)
        {
            array.MoveArrayElement (index, index + 1);
            target.ApplyModifiedProperties ();
        }
    }
}