Serializing interfaces using [SerializeReference]

[fossil flower]

I made a custom object field and an Editor that allow drawing interfaces, which I am serializing using [SerializeReference],
but when I drag a monobehaviour implementing the interface and set the value of the interface field I get the error:
"Fields with [SerializeReference] cannot serialize objects that derive from Unity.Object".
Is there any way to fix this?

[elder lotus]

Unity does not offer a serialization implementation for direct Interface references

[fossil flower]

Is there any way for me to add serialization of interfaces, without using callback on every class implementing it?

[cedar sand]

SerializeReference can serialize interfaces just fine. What it can’t do is reference anything that inherits UnityEngine.Object, like MonoBehaviour and ScriptableObject.

It’s only for serializing classes/structs.

[flint bear]

You could always add a wrapper object that implements your interface and accept Unity.Object

You would obviously have to add a property drawer to limit what you can drag into the field

[fossil flower]

So there is no way of serializing an interface directly without a wrapper class and have it support unity Objects?

[tulip spoke]

No. I tend to use a wrapper like InterfaceObject<ISomething> which just draws one field and when you drop a ref it validates if it's of the right type and if not it just ignores it. And you can retrieve the typed ref like field.Object (yes, Object is a somewhat boring name, I know 😄 )

[fossil flower]

But i still need serializereference to serialize generics right?

[flint bear]

You cannot support both UnityEngine.Object and Serialized POCO directly. You can do 1 or the other with a PropertyDrawer, but needs a wrapper to support both.

[flint bear]

You do not "need" a SerializeReference if the object is a Unity Object

[tulip spoke]

No, you can do private InterfaceObject<ISomething> myInterfacedUnityObject;
What I'm saying is just in case you want to work with Monos or SOs by interface... [SerializeReference] is in case you want non UnityEngine.Object serialized and displayed in the inspector (which doesn't seem to be what you want?)

(In this case InterfaceObject is a single normal class with [Serialized] attribute on top, and a <T> for the interface type)

If that's what you're after, I can throw you the code

[obtuse crystal]

I do this the easy way. Serialize as Monobehaviour or Component and use OnValidate to ensure it implements the interface I want.

Ofc it requires a cast at some point but it works

[fossil flower]

No I dont want non Objects to be serialized, forgot to mention it. I already made the generic wrapper but im having trouble getting the generic stored interface from the serializedProperty in the propertydrawer. So I want to extract IInterface from wrapper<IInterface> using its SerializedProperty

[tulip spoke]

Here's my implementation of the thing, in case it helps you: https://gist.github.com/pulni4kiya/c28cbd4675abd7ac4fd78901ee5d3f13

[fossil flower]

With extracting IInterface I also mean just the type not the object instance

[tulip spoke]

But basically, you use this.fieldInfo in your property drawer to get the type.