OnBeforeSerialize is getting called rapidly?

Question

Not sure if this is normal, but I noticed that OnBeforeSerialize is getting called very rapidly in-editor and at runtime - almost every frame.

 using UnityEngine;   
 
 public class Test : MonoBehaviour, ISerializationCallbackReceiver
 {
     public void OnBeforeSerialize()
     {
         Debug.Log("before");
     }
 
     public void OnAfterDeserialize()
     {
         Debug.Log("after");
     }
 }

I read in the docs that it's called before Unity 'reads' my objects' values - I don't think 'read' is quite a synonym to 'serialize' - they're using 'read'/'write' to 'serialization'/'deserialization' - not sure about that.

Is this how it's supposed to work? (called very rapidly) - if so, I think they should have named it something else cause 'OnBeforeSerialize' is miss-leading, unless I'm miss-understanding something here.

Cheers!

EDIT:

So I thought maybe cause I'm using some Unity API (Debug.Log) which the doc states that it wouldn't be preferred - but not the case, tried this:

 public int counter;

 public void OnBeforeSerialize()
 {
     counter++;
 }

And the value still changes very rapidly!

Answer 1

Best Answer

Answer by Landern · Sep 04, 2014 at 07:10 PM

The documentation warns you that using this interface and the rapid calls right here:

Another caveat is that serialization happens more often than you might think. When a MonoBehaviour gets cloned through Instantiate() at runtime, it gets deserialized and serialized. If the object had a field that pointed to its own gameObject, when that gameObject gets cloned, you'd want the field to point to the new gameObject, not the old one. In order to update these "internal references", Unity uses the serialization system. Unity reads all your fields, finds references to "things that were cloned", and then writes the new values in your fields. The callbacks will also be invoked for this updating phase, allowing you to make the updating of internal references to also work in your custom classes that Unity cannot serialize.

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vexe · Sep 05, 2014 at 05:31 AM 1

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@Landern Yes I read that of course. It mentions that it gets called many times in many situations. But it never mentions where it gets called 'rapidly' almost each frame when the object is just sitting there doing nothing (i.e. no cloning no etc) - Have you tried the example counter script above?

Landern · Sep 05, 2014 at 03:24 PM 1

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I would next read the blog post about the introduction to ISerializationCallbackReceiver, there are a LOT of gotcha's depending on how you construct objects, what they derive from and whether unity is going to just (de)serialize ad nauseam to ensure the internal stream has the newest information. If you go through the comments on the blog post they explain quite a bit, this includes sixtrillionbillion calls and why it may be happening.

vexe · Sep 05, 2014 at 05:53 PM 0

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Thanks will take a look

sarynth · Oct 04, 2020 at 05:09 PM 0

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I started to go to the blog post linked, but the next answer below this one answered the question in my case. When I have the Inspector focused on the Scriptable Object asset, it's serializing the value every frame to display in the inspector. When I clicked to inspect something else, it stopped being called. Very cool

Answer 2

Answer by Tryz · Sep 24, 2014 at 12:40 PM

I would agree that "happens more often than you might think" doesn't really equate to "every frame".

Here's what I found for OnBeforeSerialize:

Called once before a recompile is handled by the Unity Editor
Called multiple times when the scene is saved (ie two or three times)
Called every frame if the inspector for the object is open in the editor
Not called in an actual build (in my simple test)

Here's what I found for OnAfterDeserialize:

Called once after a recompile
Called once after the scene is loaded
Called once in an actual build (in my simple test)

So, if you have the editor open and an inspector open. OnBeforeSerialize is called every frame by the OnInspectorUpdate function. So far, there doesn't seem to be a way for me to stop or interrupt this.

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Deni35 · Nov 27, 2016 at 05:20 PM 0

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What is the point to call OnBeforeSerialize every frame if inspector is opened?

Bunny83 Deni35 · Nov 27, 2016 at 05:50 PM 0

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The inspector works soley on the serialized data of the objects. It uses the SerializedObject and it's SerializedProperty objects. Each time those are "read" (whenever the inspector redraws) the serialized data need to be updated.

Sanctus2099 Bunny83 · Aug 31, 2017 at 11:53 AM 0

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That's the key there "whenever the inspector redraws". I did however add a log in the OnInspectorGUI method and one on OnBeforeSerialize. The first one is logged once or so and the other one is constantly called.

Answer 3

Answer by DaCookie · Jun 15, 2020 at 02:02 PM

This is an old thread, but here's a workaround.

I have a ScriptableObject that have some properties exposed in the inspector, but I use the serialization callbacks to serialize a non-serializable data (as an example, I'm serializing a dictionary).

In order to avoid serialization if it's not needed, I use the Unity's dirty flag. This flag is enabled when an exposed property is changed in the inspector. So if this flag is set to true (and so a property has been modified), I let the serialization happen, then I remove the dirty flag.

 public void OnBeforeSerialize()
 {
     #if UNITY_EDITOR
     if(UnityEditor.EditorUtility.IsDirty(this);
     {
         SerializeDictionary();
         UnityEditor.EditorUtility.ClearDirty(this);
     }
     #else
     SerializeDictionary();
 }
 
 private void SerializeDictionary() { /* ... */ }

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iliaJelly · Apr 13, 2021 at 06:34 AM 0

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You are onto something,

iliaJelly · Apr 13, 2021 at 08:38 AM 0

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However, according to my findings, If you do .ClearDirty() than you will prevent the Asset from being saved to Disk.

Assets are saved to disk whenever AssetDatabase.SaveAssets() is called, Or the Save Project from menu is pressed.

the IsDirty flag gets cleared by itself when asset is saved to Disk. So I would not do .ClearDirty(), this still means that it would run every frame after it was changed, and before SaveAssets() is called. But thats better than nothing

OnBeforeSerialize is getting called rapidly?

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