Editor script to make Play button always jump to a start scene

After 5.2, Unity introduced RuntimeInitializeLoadType.BeforeSceneLoad. So we can get a perfect version of this. What does the perfect mean?

• Hook into the play button. So you don't need use the menu item.

• Automatically use the currently scene changes in runtime, you don't even need to save them.

• After exit play mode, scene go back to previously editing scene. And the all the unsaved changes still there.

So here's the code,

 public static class PlayFromTheFirstScene
 {      
     const string playFromFirstMenuStr = "Edit/Always Start From Scene 0 &p";
 
     static bool playFromFirstScene
     {
         get{return EditorPrefs.HasKey(playFromFirstMenuStr) && EditorPrefs.GetBool(playFromFirstMenuStr);}
         set{EditorPrefs.SetBool(playFromFirstMenuStr, value);}
     }
 
     [MenuItem(playFromFirstMenuStr, false, 150)]
     static void PlayFromFirstSceneCheckMenu() 
     {
         playFromFirstScene = !playFromFirstScene;
         Menu.SetChecked(playFromFirstMenuStr, playFromFirstScene);
 
         ShowNotifyOrLog(playFromFirstScene ? "Play from scene 0" : "Play from current scene");
     }
 
     // The menu won't be gray out, we use this validate method for update check state
     [MenuItem(playFromFirstMenuStr, true)]
     static bool PlayFromFirstSceneCheckMenuValidate()
     {
         Menu.SetChecked(playFromFirstMenuStr, playFromFirstScene);
         return true;
     }
 
     // This method is called before any Awake. It's the perfect callback for this feature
     [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)] 
     static void LoadFirstSceneAtGameBegins()
     {
         if(!playFromFirstScene)
             return;
 
         if(EditorBuildSettings.scenes.Length  == 0)
         {
             Debug.LogWarning("The scene build list is empty. Can't play from first scene.");
             return;
         }
 
         foreach(GameObject go in Object.FindObjectsOfType<GameObject>())
             go.SetActive(false);
         
         SceneManager.LoadScene(0);
     }
 
     static void ShowNotifyOrLog(string msg)
     {
         if(Resources.FindObjectsOfTypeAll<SceneView>().Length > 0)
             EditorWindow.GetWindow<SceneView>().ShowNotification(new GUIContent(msg));
         else
             Debug.Log(msg); // When there's no scene view opened, we just print a log
     }
 }

Enjoy! Oh, also, there's some other useful tricks like how to make a checkable menu item correctly, or how to show a compile error like message in the scene view. Check them out in the code if you interested.

How about this?

In scene 0, create a game object called "Scene 0 Object" and attach this script:

 public class DontDestroyOnLoad : MonoBehaviour {
     void Start() {
         DontDestroyOnLoad(this.GameObject);
     }
 }

In your other scenes, create a game object called "Play Scene 0" and attach this script:

 public class PlayScene0 : MonoBehaviour {
     void Start() {
         if (Application.isEditor && (GameObject.Find("Scene 0 Object") == null)) {
             Application.LoadLevel(0);
         }
     }
 }

You can make this a prefab and just add the prefab to every scene.

This way you can continue using your regular play button. If you really want to run from scene 4 instead of auto-loading scene 0 on play, just disable the "Play Scene 0" object.

My approach would be to directly hook into the user pressing the play button with the following code:

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 
 [InitializeOnLoad]
 public static class LoadSceneOnPressingPlay{
     
     [SerializeField]
     public static string oldScene;
     
     static void LoadSceneOnPressingPlay(){
         EditorApplication.playmodeStateChanged += StateChange;
     }
     
     static void StateChange(){
         if(EditorApplication.isPlaying){
             EditorApplication.playmodeStateChanged -= StateChange;
             if(!EditorApplication.isPlayingOrWillChangePlaymode){
                 //We're in playmode, just about to change playmode to Editor
                 Debug.Log("Loading original level");
                 EditorApplication.OpenScene(oldScene);
             }else{
                 //We're in playmode, right after having pressed Play
                 oldScene = EditorApplication.currentScene;
                 Debug.Log("Loading first level");
                 Application.LoadLevel(0);
             }
         }
     }
 }

For the record, the alternative to LoadLevel in the Editor is

 EditorApplication.OpenScene(EditorBuildSettings.scenes[levelIndex].path);

I just went through setting up Fattie's Grid system with the Scene Auto Loader by User_Yoyo in a little video I put together.

Note: This movie shows how to rig it so when you press play, the pre-game scene gets loaded and then the scene you are working on gets automatically loaded after that.

https://www.youtube.com/watch?v=lWmk2QXy4wU

I also put a download link to the package in the movie details.

Let me know if you find any mistakes.

Share and enjoy.