Start with first scene script

Sometimes when working on a scene in Unity you do not necessarily want the play mode to start with that scene (which is the default behavior).

Instead, you may want it to start as it would in a build (aka the first scene is used).

This adds a simple on/off checkbox to the Tools menu. It is based on an idea on this unity forum thread. You can also find the source as a Gist on GitHub.

#if UNITY_EDITOR
using UnityEditor;
using UnityEngine;

using UnityEditor.SceneManagement;

namespace Kamgam
{
	/// <summary>
	/// Start With First Scene<br />
	/// Sometimes when working on a scene in Unity you do not necessarily want the play mode
	/// to start with that scene (which is the default behavior). Instead, you may want it to
	/// start as it would in a build (aka the first scene is used).<br /><br />
	/// This adds a simple on/off checkbox to the Tools menu.
	/// </summary>
	/// <description>
	/// Based on an idea on this thread:
	/// http://forum.unity3d.com/threads/157502-Executing-first-scene-in-build-settings-when-pressing-play-button-in-editor
	/// </description>
	[InitializeOnLoad]
	public static class StartWithFirstScene
	{
		private const string NAME = "Tools/Start with first scene";

		static bool isEnabled
		{
			get
			{
				return EditorPrefs.GetBool(NAME, false);
			}
			set
			{
				EditorPrefs.SetBool(NAME, value);
				SceneListChanged();
			}
		}

		[MenuItem(NAME, false, 0)]
		static void LoadFirstScene()
		{
			isEnabled = !isEnabled;
		}

		[MenuItem(NAME, true, 0)]
		static bool ValidateLoadFirstScene()
		{
			Menu.SetChecked(NAME, isEnabled);
			return true;
		}

		static StartWithFirstScene()
		{
			SceneListChanged();

			EditorBuildSettings.sceneListChanged += SceneListChanged;
		}

		static void SceneListChanged()
		{
			if (!isEnabled)
			{
				EditorSceneManager.playModeStartScene = default;
				return;
			}
			//Ensure at least one build scene exist.
			if (EditorBuildSettings.scenes.Length == 0)
			{
				Debug.Log("No Scenes in Build Settings");
				isEnabled = false;
				return;
			}
			//Reference the first scene
			SceneAsset theScene = AssetDatabase.LoadAssetAtPath<SceneAsset>(EditorBuildSettings.scenes[0].path);
			// Set Play Mode scene to first scene defined in build settings.
			EditorSceneManager.playModeStartScene = theScene;
		}
	}
}
#endif

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