"type is not a supported pptr value" when editing a list in the editor

I’m not sure this can be done at all, but here’s what I’m trying to do:

My component has several properties (public fields) which are editable in the Editor. One of those should be a list containing a specific class, and I’m trying to make this list, and especially the fields of the objects contained in that list editable in the Editor.

The component looks like this:

[Serializable]
public class DialogmenuControllerReponse {
    public TextMeshProUGUI Icon;
    public TextMeshProUGUI Text;
}

public class DialogMenuController : MonoBehaviour
{
    // ...
    [Expandable]
    public List<DialogmenuControllerReponse> Responses;
}

However, if I leave it like that, I get the “type is not a supported pptr value” exception in the editor when I try to expand the fields in the editor. There’s also some GUI corruption:

except for the GUI corruption which makes the fields non-editable, and the exception, that’s pretty much exactly what I want - to create a list of a certain size and to edit the fields in its objects in the Editor.

If I derive the DialogmenuControllerReponse class (whose instances are in the list) from UnityEngine.Object or a ScriptableObject, the editor shows a list of None objects (pretty much null references, right?):

And I can’t seem to create those elements in-place. I’m NOT looking for a solution where I create ScriptableObjects in the file system and drag&drop them here. I’m looking for a way to edit the fields of those elements in the preceding images (which might involve creating those elements somehow in the first place).

Your code as presented here should work… except that I’ve never seen the “Expandable” attribute, and such an attribute should not be needed. Lists show up as you describe by default. Have you tried without that attribute?

For what it’s worth I copied your exact code (except removing the “Expandable” attribute), and it worked perfectly:

6220161--683946--upload_2020-8-18_19-55-14.png