How to add elements to a SerializedProperty that refernces a List where T : is a Serializable 'regular' class?

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Hello,

I have a SerializedProperty that is referencing a List, where Decision is just a regular class (Not a MonoBehaviour, nor a ScriptableObject) mocked with [System.Serializable]

The problem I'm facing, I can't add new decisions!

Well, the way one would add something to a list that's referenced via a SerializedProperty is to manually increase the size of the array (via arraySize), and then set the last element directly, a method to do that would be (for strings):

 public static void Add(this SerializedProperty prop, string value)
 {
     prop.arraySize++;
     prop.GetAt(prop.arraySize - 1).stringValue = value;
 }

The problem is that I can't do this to add my Decision object:

     prop.arraySize++;
     prop.GetAt(prop.arraySize - 1).objectReferenceValue = value;

Because, objectReferenceValue is a UnityEngine.Object, while Decision is a System.Object There's no way to convert from the first to the second.

There are obvious ways around this, one to make the Decision class a ScriptableObject that way it is a UnityEngine.Object, other is to just get a direct reference to the list and just add the element - but then I would have to register undo manually.

I would really love to just keep my class a normal class, and be able to add it to the list via the SerializedProperty

Any ideas?

Thanks!

Answer 1

Best Answer

Answer by vexe · Feb 14, 2014 at 10:22 PM

Found the solution! - I was just watching this video for the 3rd time maybe, when I noticed @29:40, he's just incrementing the arraySize to add a new entry. But then I said oh well, that's because the entry is probably a ScriptableObject, but... surprise surprise @30:19 - it's a normal class!

Couple of things to take note of:

Doing a size increment like that will duplicate the last element in the array/list.
If after the increment you wanted to 'directly' access the element you added, you have to do a serializedObject.ApplyModifiedProperties(); so that the change will get reflected on the actual target object.
Not a horrible thing to notice, but you should put the initialization logic of your object (in my case Decision) in its constructor since you can't really get a reference to it via the SerializedProperty to call some Init method (if there's a method you'd want to call, you have to call it directly like (target as MyClass).Field.Method(); )

So yeah that's about it, arraySize++

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instruct9r · Dec 08, 2015 at 01:29 PM 0

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Heya @vexe this is cool, thanks for sharing

Anyway i wonder... How can i perform List.Remove(index) with the _serializedProperty...

Because if i try to do

 _serializedProperty.DeleteArrayElementAtIndex(index)

It removes the reference of the index, but doesn't actually removes the index, but leaves it empty...

The only way i found, doing it is by moving the index to the last position and then do arraySize--:

 if (_serializedProperty.GetArrayElementAtIndex(index).objectReferenceValue != null)
     _serializedProperty.DeleteArrayElementAtIndex(index);
 
 _serializedProperty.$$anonymous$$oveArrayElement(index, _serializedProperty.arraySize -1);
 _serializedProperty.arraySize--;

I was wondering if there is another way...

vexe · Dec 08, 2015 at 07:33 PM 2

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@instruct9r Yeah I remember that. Another way is to call DeleteArrayElementAtIndex twice on the same index, second time's the charm! Another way is to forget about SerializedProperties altogether, and don't use them. Awful API.

ModLunar · Jun 04, 2018 at 04:54 AM 0

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As always, thanks for your very insightful answers! They need you on the Unity documentation $$anonymous$$m to write details like these :P

Bubsavvy · Sep 27, 2019 at 08:17 AM 0

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@vexe as of Unity 2019.1.9f1 this see$$anonymous$$gly does not work. :C Whenever you increment on the next call to OnGUI the property is indeed not updated. Really annoying actually unless i am missing something. I already tried prop.serializedObject.Apply$$anonymous$$odifiedProperties as well

How to add elements to a SerializedProperty that refernces a List where T : is a Serializable 'regular' class?

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