Setting ManagedReference to null value breaks TrackPropertyValue notifications.

Unity Engine
,
1

This is a bit of a tricky issue to summarize in a title, but after testing I’m fairly sure it’s a bug. I have a class, SPUndo, and it has a reference to a subclass, SPUndoSubclass.

public class SPUndoSubclass
{
    public int primitive;
}

public class SPUndo : MonoBehaviour
{
    [SerializeReference]
    SPUndoSubclass reference;
}

I’m trying to add and remove an instance of SPUndoSubclass. Click the [+] button to create an instance, click [-] to remove it. Here’s the issue:

  1. When the editor UI is created and reference != null: every modification to reference triggers a notification.
  2. When the editor UI is created and reference == null: Assigning a new instance to reference triggers an event. However, no subsequent change (which entails = null) sends a notification. This is the issue. Here’s the example code below:
[CustomEditor(typeof(SPUndo))]
public class SPUndoInspector : Editor
{
    private Button AddButton;
    private Button RemoveButton;
    private PropertyField PrimitiveField;

    public override VisualElement CreateInspectorGUI()
    {
        VisualElement visualInput = new VisualElement();

        AddButton = new Button(AddButton_clicked);
        AddButton.text = "+";

        RemoveButton = new Button(RemoveButton_clicked);
        RemoveButton.text = "-";

        PrimitiveField = new PropertyField();

        SerializedProperty referenceProperty = serializedObject.FindProperty("reference");
        ReferenceChangedCallback(referenceProperty);
        BindingExtensions.TrackPropertyValue(visualInput, referenceProperty, ReferenceChangedCallback);

        visualInput.Add(AddButton);
        visualInput.Add(RemoveButton);
        visualInput.Add(PrimitiveField);

        return visualInput;
    }

    void ReferenceChangedCallback(SerializedProperty property)
    {
        UnityEngine.Debug.Log("ReferenceChangedCallback");

        PrimitiveField.Unbind();

        if (property.managedReferenceValue == null)
        {
            AddButton.SetEnabled(true);
            RemoveButton.SetEnabled(false);

            PrimitiveField.visible = false;
        }
        else
        {
            AddButton.SetEnabled(false);
            RemoveButton.SetEnabled(true);

            PrimitiveField.visible = true;
            BindingExtensions.BindProperty(PrimitiveField, property.FindPropertyRelative("primitive"));
        }
    }

    private void AddButton_clicked()
    {
        serializedObject.Update();
        serializedObject.FindProperty("reference").managedReferenceValue = new SPUndoSubclass();
        serializedObject.ApplyModifiedProperties();
    }

    private void RemoveButton_clicked()
    {
        serializedObject.Update();
        serializedObject.FindProperty("reference").managedReferenceValue = null;
        serializedObject.ApplyModifiedProperties();
    }
}
2

please feel free to log a bug we’ll take a look at it