Unity - Snapping created GameObjects

SnapOnCreateToolbarToggle.cs

if UNITY_EDITOR
namespace LBG.EditorUtils.Editor
{
	using UnityEngine;
	using UnityEditor;
	using UnityEditor.Toolbars;
	using UnityEngine.UIElements;

	[EditorToolbarElement(SnapOnCreateToolbarToggle.id, typeof(SceneView))]
	internal sealed class SnapOnCreateToolbarToggle : EditorToolbarToggle
	{
		public const string id = "Snapping/SnapOnCreate";

		public SnapOnCreateToolbarToggle() : base()
		{
			text = "Snap On Create";
			tooltip = "Toggles whether game objects are always automatically snapped to the grid on creation.";
			icon = (Texture2D)EditorGUIUtility.Load("d_SceneViewSnap");
			bool snapOnCreate = SnapSettings.instance.SnapOnCreate;
			this.SetValueWithoutNotify(snapOnCreate);
			this.RegisterValueChangedCallback<bool>(HandleToggleEvent);
		}

		private void HandleToggleEvent(ChangeEvent<bool> e)
		{
			SnapSettings.instance.SnapOnCreate = e.newValue;
		}
	}
}
#endif

SnappingToolbar.cs

#if UNITY_EDITOR
namespace LBG.EditorUtils.Editor
{
	using UnityEditor;
	using UnityEditor.Overlays;

	[Overlay(typeof(SceneView), "Snapping Tools")]
	internal sealed class SnappingToolbar : ToolbarOverlay
	{
		public SnappingToolbar() : base(SnapOnCreateToolbarToggle.id) { }
	}
}
#endif

SnappingTracker.cs

#if UNITY_EDITOR
namespace LBG.EditorUtils.Editor
{
	using UnityEngine;
	using UnityEditor;

	[InitializeOnLoad]
	internal static class SnappingTracker
	{
		static SnappingTracker()
		{
			ObjectChangeEvents.changesPublished += HandleCreatedGameObjects;
		}

		private static void HandleCreatedGameObjects(ref ObjectChangeEventStream stream)
		{
			int length = stream.length;
			for (int i = 0; i < length; i++)
			{
				var eventType = stream.GetEventType(i);
				if (eventType == ObjectChangeKind.CreateGameObjectHierarchy)
				{
					stream.GetCreateGameObjectHierarchyEvent(i, out var createdGameObjectsEvent);
					int instanceID = createdGameObjectsEvent.instanceId;

					if (AssetDatabase.Contains(instanceID) == true) // don't want to snap assets
					{
						return;
					}

					var createdGameObject = EditorUtility.InstanceIDToObject(instanceID) as GameObject;
					var snaps = new Transform[] { createdGameObject.transform };
					Handles.SnapToGrid(snaps);
				}
			}
		}
	}
}
#endif

SnapSettings.cs

#if UNITY_EDITOR
namespace LBG.EditorUtils.Editor
{
	using System.Collections;
	using System.Collections.Generic;
	using UnityEditor;
	using UnityEngine;

	[FilePath("Library/LBGSnapSettings.asset", FilePathAttribute.Location.ProjectFolder)]
	public sealed class SnapSettings : ScriptableSingleton<SnapSettings>
	{
		#region Inspector Fields

		[SerializeField]
		private bool _snapOnCreate;

		#endregion

		#region Properties

		public bool SnapOnCreate
		{
			get => _snapOnCreate;
			set => _snapOnCreate = value;
		}

		#endregion

		private void OnDisable()
		{
			this.Save(true);
		}
	}
}
#endif