Loading and unloading multiple scenes with AsyncOperation

Unity Engine
,
1

Hi everyone! I’m developing a room system for a Metroidvania game. Each room was made in a separate scene, and when the player enters the room bounds, it loads all scenes nearby that room and unloads all scenes far away.

Loads the scenes:

IEnumerator LoadNearbyScenesAsync()
    {
        List<AsyncOperation> sceneLoads = new List<AsyncOperation>();
        for (int i = 0; i < nearbyRoomsName.Count; ++i)
        {

            if (!SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded().Contains(nearbyRoomsName[i]))
            {
                AsyncOperation sceneLoading = SceneManager.LoadSceneAsync(nearbyRoomsName[i], LoadSceneMode.Additive);
                sceneLoading.allowSceneActivation = false;
                sceneLoads.Add(sceneLoading);

                while (sceneLoads[i].progress < 0.9f)
                {
                    yield return null;
                }
            }
        }
        for (int i = 0; i < sceneLoads.Count; ++i)
        {

            sceneLoads[i].allowSceneActivation = true;
            while (!sceneLoads[i].isDone)
            {
                yield return null;
            }
            if (!SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded().Contains(this.gameObject.scene.name))
            {
                SceneHandler.sceneHandlerInstance.SetSceneAsLoaded(nearbyRoomsName[i]);
            }
        }
        UnloadFarLevels();

    }

Unloads the scenes:

 IEnumerator UnloadFarScenes()
    {
        List<AsyncOperation> sceneUnloads = new List<AsyncOperation>();


        for (int i = 0; i < SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded().Count; ++i)
        {
            if (!nearbyRoomsName.Contains(SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded()[i]))
            {
                AsyncOperation sceneUnloading = SceneManager.UnloadSceneAsync(SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded()[i]);
                sceneUnloads.Add(sceneUnloading);
                SceneHandler.sceneHandlerInstance.SetSceneAsUnloaded(SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded()[i]);

                while (!sceneUnloads[i].isDone)
                {
                    yield return null;
                }
            }
        }
    }

It is working kinda well, but sometimes I get an Out of Range Exception, and some scenes start loading, but never loads. Should be some silly logic mistake, any ideias on what should it be?

2

Here are some notes on IndexOutOfRangeException and ArgumentOutOfRangeException:

http://plbm.com/?p=236

Steps to success:

  • find which collection it is (critical first step!)
  • find out why it has fewer items than you expect
  • fix whatever logic is making the indexing value exceed the collection
  • remember you might have more than one instance of this script in your scene/prefab

You must find a way to get the information you need in order to reason about what the problem is.

Once you understand what the problem is, you may begin to reason about a solution to the problem.

What is often happening in these cases is one of the following:

  • the code you think is executing is not actually executing at all
  • the code is executing far EARLIER or LATER than you think
  • the code is executing far LESS OFTEN than you think
  • the code is executing far MORE OFTEN than you think
  • the code is executing on another GameObject than you think it is
  • you’re getting an error or warning and you haven’t noticed it in the console window

To help gain more insight into your problem, I recommend liberally sprinkling Debug.Log() statements through your code to display information in realtime.

Doing this should help you answer these types of questions:

  • is this code even running? which parts are running? how often does it run? what order does it run in?
  • what are the values of the variables involved? Are they initialized? Are the values reasonable?
  • are you meeting ALL the requirements to receive callbacks such as triggers / colliders (review the documentation)

Knowing this information will help you reason about the behavior you are seeing.

You can also supply a second argument to Debug.Log() and when you click the message, it will highlight the object in scene, such as Debug.Log("Problem!",this);

If your problem would benefit from in-scene or in-game visualization, Debug.DrawRay() or Debug.DrawLine() can help you visualize things like rays (used in raycasting) or distances.

You can also call Debug.Break() to pause the Editor when certain interesting pieces of code run, and then study the scene manually, looking for all the parts, where they are, what scripts are on them, etc.

You can also call GameObject.CreatePrimitive() to emplace debug-marker-ish objects in the scene at runtime.

You could also just display various important quantities in UI Text elements to watch them change as you play the game.

If you are running a mobile device you can also view the console output. Google for how on your particular mobile target, such as this answer or iOS: https://discussions.unity.com/t/700551 or this answer for Android: https://discussions.unity.com/t/699654

Another useful approach is to temporarily strip out everything besides what is necessary to prove your issue. This can simplify and isolate compounding effects of other items in your scene or prefab.

Here’s an example of putting in a laser-focused Debug.Log() and how that can save you a TON of time wallowing around speculating what might be going wrong:

https://discussions.unity.com/t/839300/3

When in doubt, print it out!™

Note: the print() function is an alias for Debug.Log() provided by the MonoBehaviour class.

3

Found the problem, the null exceptions were due to IEnumerator and yield return, causing problems at adding values to the list. Swapped to this and worked:

 public void LoadNearbyLevels()
   {
        for (int i = 0; i < nearbyRoomsName.Count; ++i)
        {
            if (!SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded().Contains(nearbyRoomsName[i]))
            {
                AsyncOperation sceneLoading = SceneManager.LoadSceneAsync(nearbyRoomsName[i], LoadSceneMode.Additive);
                SceneHandler.sceneHandlerInstance.SetSceneAsLoaded(nearbyRoomsName[i]);
            }
        }
        UnloadFarLevels();
    }
   private void UnloadFarLevels()
    {
        for (int i = 0; i < SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded().Count; ++i)
        {
            if (!nearbyRoomsName.Contains(SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded()[i])
                && this.gameObject.scene.name != SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded()[i])
            {
                AsyncOperation sceneUnloading = SceneManager.UnloadSceneAsync(SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded()[i]);
                SceneHandler.sceneHandlerInstance.SetSceneAsUnloaded(SceneHandler.sceneHandlerInstance.GetCurrentScenesLoaded()[i]);
            }
        }
    }