Question Cancel async AssetReference instantiation on scene change.

Hello all. I have a problem in my project. I can't reproduce it on my PC, but I have a theory of what is the reason.
Imagine an AssetReference which instntiates right after the scene is loaded.

Code (CSharp):

1. public static async Task InstantiateAssetsAddToList<T>(IEnumerable<AssetReference> AssetReferences, List<T> AssetsList) where T : UnityEngine.Object
2. {
3.     foreach (AssetReference reference in AssetReferences)
4.     {
5.         AssetsList.Add(await reference.InstantiateAsync().Task as T);
6.     }
7. }

But before the async instantiation completes, the player returns to the previous scene (clicks 'return to main menu') and the instantiation ends in the environment of the scene, which can't accept the instantiated object. This causes a lot of errors.
Can the described scenario exist in real life? How to cancel AssetReference instantiation in case of scene change?
Thanks in advance.

 

Line 5 should probably be broken into two steps:

- await the task and get the thing back

- add it to the AssetsList

This gives you an opportunity to reason about whether you should still proceed with adding it, and perhaps to put an interlock (via OnDisable() for instance) that sets AssetsList null so it won't add to it.

Beyond that, you gotta debug some more and find out exactly where it is blowing up.

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://forum.unity.com/threads/how-to-capturing-device-logs-on-ios.529920/ or this answer for Android: https://forum.unity.com/threads/how-to-capturing-device-logs-on-android.528680/

If you are working in VR, it might be useful to make your on onscreen log output, or integrate one from the asset store, so you can see what is happening as you operate your software.

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://forum.unity.com/threads/coroutine-missing-hint-and-error.1103197/#post-7100494

When in doubt, print it out!(tm)

Note: the

print()

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

 

Thank you. I can check for the scene name condition before adding it to the list. But at this point my objects will already be instantiated and their Await/Start methods will be called causing errors. Am I wrong?
I was thinking about something like CancellationTokenSource in C# that can be used to cancel Tasks. But while Addressables supports C# Tasks, I can't find a way to cancel Addressables async operations.