Unity Reparent To Selection

ReparentToSelected.cs

using System.Linq;
using UnityEditor;
using UnityEngine;

[InitializeOnLoad]
public class ReparentToSelected
{
    private static GameObject[] _lastSelection;
    private static GameObject[] _secondLastSelection;

    static ReparentToSelected()
    {
        Selection.selectionChanged += OnSelectionChanged;
    }

    private static void OnSelectionChanged()
    {
        _secondLastSelection = _lastSelection;
        _lastSelection = Selection.gameObjects;
    }


    [MenuItem("GameObject/Reparent To Selected", false, 0)]
    public static void InvokeAction()
    {
        GameObject parent = Selection.activeGameObject;

        Undo.SetCurrentGroupName("Reparent to Selected");
        int group = Undo.GetCurrentGroup();
        {
            foreach (GameObject child in _secondLastSelection)
            {
                Undo.SetTransformParent(
                    child.transform,
                    parent.transform,
                    "Reparent to Selected"
                );
            }
        }
        Undo.CollapseUndoOperations(group);

        Selection.objects = _secondLastSelection.Cast<Object>().ToArray();
    }

    [MenuItem("GameObject/Reparent To Selected", true)]
    public static bool ValidateInvokeAction()
    {
        if (_secondLastSelection == null)
            return false;

        if(_lastSelection == null || _lastSelection.Length != 1)
            return false;

        return true;
    }
}