ListView seems completely broken

Unity Engine
,
1

I’ve just reported a bug about ListView, but I’m kinda surprised, because what I thought would be a complicated repro case ended up being very simple, and the bug seems to be present on 2022 and 2023.

My script is this:

public class TestScript : MonoBehaviour
{
    public string[] strings;
}

And the editor is this:

[CustomEditor(typeof(TestScript))]
public class TestScriptEditor : Editor
{
    public override VisualElement CreateInspectorGUI()
    {
        var root = new VisualElement();
        var listView = new ListView();

        root.Add(listView);

        listView.BindProperty(serializedObject.FindProperty(nameof(TestScript.strings)));
        return root;
    }
}

If I add the TestScript to a GameObject, the result is:

9557371--1351201--upload_2024-1-2_10-30-27.png
9557371--1351201--upload_2024-1-2_10-30-27.png897×51 8.81 KB

The full stack trace is this:

ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
System.Collections.Generic.List1[T].get_Item (System.Int32 index) (at <1334a096378c46d2bd2be2db1a37116e>:0) UnityEngine.UIElements.VerticalVirtualizationController1[T].ReleaseItem (System.Int32 activeItemsIndex) (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.FixedHeightVirtualizationController`1[T].Resize (UnityEngine.Vector2 size) (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.BaseVerticalCollectionView.Resize (UnityEngine.Vector2 size) (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.BaseVerticalCollectionView.PostRefresh () (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.BaseListView.PostRefresh () (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.BaseVerticalCollectionView.RefreshItems () (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEditor.UIElements.Bindings.ListViewSerializedObjectBinding.SetBinding (UnityEngine.UIElements.ListView targetList, UnityEditor.UIElements.Bindings.SerializedObjectBindingContext context, UnityEditor.SerializedProperty prop) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.ListViewSerializedObjectBinding.CreateBind (UnityEngine.UIElements.ListView listView, UnityEditor.UIElements.Bindings.SerializedObjectBindingContext context, UnityEditor.SerializedProperty prop) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.BindListView (UnityEngine.UIElements.ListView listView, UnityEditor.SerializedProperty prop) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.CreateBindingObjectForProperty (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedProperty prop) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.BindPropertyRelative (UnityEngine.UIElements.IBindable field, UnityEditor.SerializedProperty parentProperty) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.BindTree (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedProperty parentProperty) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.ContinueBinding (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedProperty parentProperty) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.Bind (UnityEngine.UIElements.VisualElement element) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEditor.UIElements.Bindings.DefaultSerializedObjectBindingImplementation+BindingRequest.Bind (UnityEngine.UIElements.VisualElement element) (at <6b1405e82d454258a8fbde4cb0621937>:0)
UnityEngine.UIElements.VisualTreeBindingsUpdater.Update () (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.VisualTreeUpdater.UpdateVisualTreePhase (UnityEngine.UIElements.VisualTreeUpdatePhase phase) (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.Panel.UpdateBindings () (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.UpdateSchedulers () (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEngine.UIElements.UIEventRegistration.UpdateSchedulers () (at <5566f9e97c3b47c3802abbb5405c3a92>:0)
UnityEditor.RetainedMode.UpdateSchedulers () (at <6b1405e82d454258a8fbde4cb0621937>:0)

I looked at the code in a debugger, and it’s a simple thing where it tries to remove the current elements when rebuilding, but there are none to remove, so it breaks.

The same bug happens if I use a bindingPath and bind the SerializedObject, and if I create a ListView by loading a uxml file.

In addition to this slightly annoying bug, I have a worse one where if I go to debug mode and add some values:

9557371--1351204--upload_2024-1-2_9-44-52.png

The result when I switch back to non-debug mode is:

9557371--1351207--upload_2024-1-2_9-45-21.png

So it can’t even display the elements correctly!

Is the ListView not ready to use? This set of bugs is so severe that I don’t quite understand how they happened for a production ready product.

2

Directly binding to a collection property hasn’t ever really seemed to work for me, as it seems to try and include the array size as an element in the list???

Last time I used a ListView I had to go through this sorta rigmarole (example from a scene organiser tool of mine):

private void BuildSceneGroupsDisplay()
{
    _sceneGroupsContainer.Clear();

    var serialisedSettings = new SerializedObject(_settings);
    _groupListProperty = serialisedSettings.FindProperty("_sceneGroups");
    _groupListView = new ListView()
    {
        showBoundCollectionSize = false,
        reorderable = false,
        selectionType = SelectionType.None,
        virtualizationMethod = CollectionVirtualizationMethod.DynamicHeight
    };
    _groupListView.makeItem += MakeSceneGroupElement;
    _groupListView.destroyItem += RemoveSceneGroupElement;
    _groupListView.bindItem += BindSceneGroup;
    _groupListView.BindProperty(_groupListProperty);
    _sceneGroupsContainer.Add(_groupListView);
}

private SceneOrganiserGroupVisualElement MakeSceneGroupElement()
{
    var group = new SceneOrganiserGroupVisualElement();
    _groupElements.Add(group);
    return group;
}

private void RemoveSceneGroupElement(VisualElement ve)
{
    var groupElement = (SceneOrganiserGroupVisualElement)ve;
    _groupElements.Remove(groupElement);
}

private void BindSceneGroup(VisualElement ve, int index)
{
    var groupElement = (SceneOrganiserGroupVisualElement)ve;
    var property = _groupListProperty.GetArrayElementAtIndex(index);
    groupElement.BindSceneGroupProperty(property);
}

Namely bit I imagine to be important is the BindSceneGroup method, that specifically pulls the right serialised properties from the collection, and then I manually bind it to my custom visual element.

No errors but it’s a lot of code, so I do wonder if this is the expected workflow? If so it could really use some streamlining.

This was my first time using ListView for an editor purpose, admittedly.

3

Thanks! Is keeping the list of group elements necessary for that functionality, or are you using it somewhere else?

I found an update for my issue - if I include the foldout header (which includes the number field), the bugs go away.
If I’m to guess, a bunch of the code assumes that the number field is present, and skips it in order to get to the correct index.

4

I was using them elsewhere so I don’t think it’s necessary.