Question by Neuron_Unity · Aug 21, 2020 at 02:26 PM · ui inspector serialization lists persistence

UIElements: problems with inserting and deleting obejcts in an array

I am trying to troubleshoot a problem in my custom Inspector. I am manipulating a List through SerializedPropertys. At some point it seems like an object ends up multiple times in the same list. I have spent hours debugging, but I can't figure it out.. Hope someone can help

These are two classes, one references a List of the other

 using System.Collections.Generic;
 using UnityEngine;
 
 public class Foo : MonoBehaviour {
     public List<Bar> list = new List<Bar>();
 }
 
 [System.Serializable]
 public class Bar {
     public string value;
 }

My Editor just lists the Bar objects. I also provides a button to append to the end of the List and remove elements. It looks like so..

 using UnityEditor.UIElements;
 using UnityEngine.UIElements;
 using UnityEditor;
 
 [CustomEditor(typeof(Foo))]
 public class FooEditor : Editor {
     SerializedProperty listProperty;
     Foo foo;
 
     VisualElement container;
     VisualElement listContainer;
 
     private void OnEnable() {
         listProperty = serializedObject.FindProperty("list");
         container = new VisualElement();
         listContainer = new VisualElement();
         foo = (Foo)target;
     }
 
     public override VisualElement CreateInspectorGUI() {
         for (int i = 0; i < listProperty.arraySize; i++) {
             SerializedProperty sp = listProperty.GetArrayElementAtIndex(i);
             SetupBarProperty(sp);
         }
         Button newStageButton = new Button(() => {
             CreateBar(listProperty.arraySize);
         });
         newStageButton.text = "Add new Bar";
         container.Add(listContainer);
         container.Add(newStageButton);
         return container;
     }
 
     public void CreateBar(int index) {
         serializedObject.Update();
 
         listProperty.InsertArrayElementAtIndex(index);
         SetupBarProperty(listProperty.GetArrayElementAtIndex(index));
         serializedObject.ApplyModifiedProperties();
         container.Bind(serializedObject);
     }
 
     private void DeleteBar(int index) {
         serializedObject.Update();
 
         listProperty.DeleteArrayElementAtIndex(index);
         listContainer.RemoveAt(index);
         serializedObject.ApplyModifiedProperties();
         container.Bind(serializedObject);
     }
 
     private void SetupBarProperty(SerializedProperty barProperty) {
         VisualElement row = new VisualElement();
         row.style.flexDirection = FlexDirection.Row;
         PropertyField stageField = new PropertyField(barProperty);
         stageField.style.flexGrow = 1;
         Button removeButton = new Button(() => { DeleteBar(listContainer.IndexOf(row)); });
         removeButton.text = "-";
 
         row.Add(stageField);
         row.Add(removeButton);
 
         listContainer.Add(row);
     }
 }

To reproduce the error:

Apply Foo to an object and open it in the inspector
Insert 2 new items
Give them distinguishable names (like E0 and E1)
Delete element at position 0 ( E0 )
Insert a new element
Change name of any of the two elements and the other will change at the same time