PrefabUtility.prefabInstanceUpdated delegate (why not event?)

Not sure this is new functionality in 2018.3, but still:
In PrefabUtility we have this static delegate field:

Code (CSharp):

1.  public static PrefabUtility.PrefabInstanceUpdated prefabInstanceUpdated;

Why was this made public static, and not public static event? Basically this can be nulled or accessed from outside of this class.

 

I don’t think this was introduced in the beta. The same pattern (delegate but no event) is repeated throughout the editor API. Maybe performance reasons or the way these are called from C++? I would also assume that they override the behaviours, so we can’t break it by setting it null (edit: this assumption is wrong, we can break these delegates). I would be interested to know as well why this was chosen and not events.

 

You can break it by setting it to null. For example - my code sets the delegate to something, but some other plugin or 3rd party codes deletes that.

 

I can confirm this and that it's also true for

EditorApplication.delayCall

. I agree, that those should rather be events or implemented to not allow breaking Unity callbacks from user code.

 

I know, so when creating new APIs, it's better to not repeat past mistakes all over again.

 

This event no longer works on 2018.3. Any alternatives?

 

@SteenLund

Version 2018.3.0f2 Windows

Here is my code under Editor folder:

Code (CSharp):

1. [InitializeOnLoad]
2. public static class MyEditorTool
3. {
4.     static MyEditorTool()
5.     {
6.         PrefabUtility.prefabInstanceUpdated += OnPrefabInstanceUpdated;
7.     }
8.  
9.    
10.     static void OnPrefabInstanceUpdated(GameObject instance)
11.     {
12.         Debug.Log("Prefab update: " + instance);
13.     }
14. }

Nothing output when I was going to save my prefab via the 'Save' button at the top of scene window.
It used to be working on the previous version with the old 'Apply' button on the inspector window.

 

I found a way to make it work.
Only the

PrefabUtility.SaveAsPrefabAssetAndConnect

will fire this event.

PrefabUtility.SaveAsPrefabAsset

or click 'Save' button in the scene window or Ctrl + S won't fire this event.

 

Any alternatives for SaveAsPrefabAsset?

 

@SteenLund, I can't speak for other users, but I've been looking for a hook when a prefab is saved that gives me the actual prefab object.

I tried OnWillSaveAssets in a custom AssetModificationProcessor class, as I've done for scenes, but I haven't been able to find the equivalent of EditorSceneManager.GetSceneByPath for a prefab.

I intuited that prefabInstanceUpdated would be called at save, but discovered, as discussed above, that it is not.

To others: the best practice when hooking a single-cast delegate is to store the old value, and call it (if it exists) internally:

Code (CSharp):

1.     [InitializeOnLoad]
2.     public class PrefabChanged
3.     {
4.         private static PrefabUtility.PrefabInstanceUpdated _oldUpdated;
5.  
6.         static PrefabChanged()
7.         {
8.             if (!Application.isPlaying)
9.             {
10.                 _oldUpdated = PrefabUtility.prefabInstanceUpdated;
11.                 PrefabUtility.prefabInstanceUpdated = InstanceUpdated;
12.             }
13.         }
14.  
15.         private static void InstanceUpdated(GameObject instance)
16.         {
17.             _oldUpdated?.Invoke(instance);
18.             //... other stuff
19.         }
20.     }