SceneManager.activeSceneChanged never called

Hi people, I have following setup:

MainScene: GO with script that initiates loading other scene with the code:

Code (CSharp):

1. void Start ()
2.     {
3.         SceneManager.sceneLoaded += SceneManager_sceneLoaded;
4.         SceneManager.activeSceneChanged += SceneManager_activeSceneChanged;
5.         SceneManager.LoadScene(2, LoadSceneMode.Additive);
6.     }

SceneManager_sceneLoaded is called and then I do:

Code (CSharp):

1. void SceneManager_sceneLoaded(Scene arg0, LoadSceneMode arg1)
2.     {
3.         SceneManager.SetActiveScene(arg0);
4.     }

SetActiveScene returns "false" and activeSceneChanged is never called.

How should I chain these events to make it work: I'd like to load scene, and once it's loaded to activate it and then do things to loaded scene objects?

Edit: I'm working with latest Unity version 5.4.0f3

 

How did you fix this?

 

SceneManager.activeSceneChanged is called when you change which scene is active when several scenes are loaded at once (through additive loading)... I believe.

Honestly, the documentation on the SceneManager stuff is very sparse. It mentions the active scene a bunch, without explaining what that means.

 

Ok I created 2 simple Scenes and added a GameObject to Scene one and attached this script:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using UnityEngine.Events;
4. using UnityEngine.EventSystems;
5. using UnityEngine.UI;
6. using UnityEngine.SceneManagement;
7.  
8. public class ActionTest : MonoBehaviour
9. {
10.    void Start()
11.     {
12.         SceneManager.sceneLoaded += SceneManager_sceneLoaded;
13.         SceneManager.activeSceneChanged += SceneManager_activeSceneChanged;
14.         SceneManager.LoadScene("Scene2", LoadSceneMode.Additive);
15.     }
16.  
17.     void SceneManager_sceneLoaded(Scene arg0, LoadSceneMode arg1)
18.     {
19.         if (SceneManager.SetActiveScene(arg0))
20.             Debug.Log(arg0.name + " set to Active:  Success");
21.         else
22.             Debug.Log(arg0.name + " set to Active: Failed");
23.     }
24.  
25.     void SceneManager_activeSceneChanged(Scene arg0, Scene arg1)
26.     {
27.         Debug.Log("Active Scene Changed");
28.     }
29. }

I get a failed debug message. So like many things with Unity when there is a lot of stuff going on in the background I decided to wait 1 Frame then try with this code:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using UnityEngine.Events;
4. using UnityEngine.EventSystems;
5. using UnityEngine.UI;
6. using UnityEngine.SceneManagement;
7.  
8. public class ActionTest : MonoBehaviour
9. {
10.    void Start()
11.     {
12.         SceneManager.sceneLoaded += SceneManager_sceneLoaded;
13.         SceneManager.activeSceneChanged += SceneManager_activeSceneChanged;
14.         SceneManager.LoadScene("Scene2", LoadSceneMode.Additive);
15.     }
16.  
17.     void SceneManager_sceneLoaded(Scene arg0, LoadSceneMode arg1)
18.     {
19.         StartCoroutine(LoadScene(arg0));
20.     }
21.  
22.     void SceneManager_activeSceneChanged(Scene arg0, Scene arg1)
23.     {
24.         Debug.Log("Active Scene Changed");
25.     }
26.  
27.     IEnumerator LoadScene(Scene scene)
28.     {
29.         yield return null;
30.         if (SceneManager.SetActiveScene(scene))
31.             Debug.Log("It worked");
32.         else
33.             Debug.Log("It didn't");
34.     }
35. }

This Gave me the Debug Message: "It Worked" as well as "Active SCene Changed".
So the trick is just stall 1 frame in a coroutine then change your active scene. Apparently Unity is sending the SceneLoaded Event a little to soon. Something isn't totally setup yet, and SceneManager.SetActive() is failing

 

That you can't react to an additive scene load by setting the scene active is either a bug, or horrendous design. I recommend that you send a bug report.