Question Question about Instatiate() inside a function called by a UnityEvent

(Unity version 2020.1.16f1 Personal)
I really don't understand why, but it doesn't seem to work like i expect it to. Can anyone explain me why?

This gives no Exceptions but does terminate the method call:

Code (CSharp):

1. using Assets.Scripts.http;
2. using UnityEngine;
3.  
4. public class TrackList : MonoBehaviour
5. {
6.     public RectTransform Content;
7.  
8.     public GameObject TrackListEntryPrefab;
9.  
10.     public TrackRequest TrackRequest;
11.  
12.     private void Start()
13.     {
14.         TrackRequest.OnResult.AddListener(SpawnList);
15.         TrackRequest.GetAllTracks();
16.     }
17.  
18.     public void SpawnList() {
19.         Instantiate(TrackListEntryPrefab, Content);
20.     }
21. }
22.  

But this does work (but it's ridiculous ofcourse):

Code (CSharp):

1. using Assets.Scripts.Model;
2. using Assets.Scripts.http;
3. using System.Collections.Generic;
4. using System.Linq;
5. using UnityEngine;
6.  
7. public class TrackList : MonoBehaviour
8. {
9.     public RectTransform Content;
10.  
11.     public GameObject TrackListEntryPrefab;
12.  
13.     public TrackRequest TrackRequest;
14.  
15.     private bool spawn = false;
16.  
17.     private void Start()
18.     {
19.         TrackRequest.OnResult.AddListener(SpawnList);
20.         TrackRequest.GetAllTracks();
21.     }
22.  
23.     private void Update()
24.     {
25.         if (spawn) {
26.             AddEntry();
27.             spawn = false;
28.         }
29.     }
30.  
31.     public void SpawnList() {
32.         spawn = true;
33.     }
34.  
35.     public void AddEntry() {
36.         Instantiate(TrackListEntryPrefab, Content);
37.     }
38. }

 

If your first posted solution failed but the second one worked, my guess would be that the event TrackRequest.OnResult is occurring on a different thread. Most UnityEngine functions are only safe to use on the main thread. Your second solution gets around this by setting a flag that is later processed by a function on the main thread.

 

Ah i see. TrackRequest.OnResult is indeed invoked on a different thread! Thanks for the info you saved me a lot more headache.