Animation from code works only once

Unity Engine
, , ,
1

Hello. I made a panel that should appear with a transparency animation and close with a transparency animation

<engine:UXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:engine="UnityEngine.UIElements" xmlns:editor="UnityEditor.UIElements" noNamespaceSchemaLocation="../../UIElementsSchema/UIElements.xsd" editor-extension-mode="False">
    <Style src="project://database/Assets/UI%20Toolkit/MyPanelStyles.uss?fileID=7433441132597879392&amp;guid=aab3325e9f53f4b0cb2fe74c5dce7609&amp;type=3#MyPanelStyles" />
    <engine:VisualElement name="MyPanel" class="my-panel">
    </engine:VisualElement>
</engine:UXML>

.my-panel {
    opacity: 0;
    transition: opacity 0.2s ease;
}

.my-panel.visible {
    opacity: 1;
}

public class MyPanelController : MonoBehaviour
    {
        public UIDocument MyPanelUIDocument { get; private set; }
        private VisualElement rootVisualElement;

        private void OnEnable()
        {
            MyPanelUIDocument = GetComponent<UIDocument>();
            rootVisualElement = MyPanelUIDocument.rootVisualElement;
        }

        public void HidePanel()
        {
            var panelElement = rootVisualElement.Q<VisualElement>("MyPanel");

            if (panelElement != null)
            {
                panelElement.RemoveFromClassList("visible");
                Debug.Log($"Panel opacity before hiding: {panelElement.resolvedStyle.opacity}");

                if (MyPanelUIDocument.enabled)
                {
                    Debug.Log("Starting coroutine to disable UIDocument.");
                    StartCoroutine(DisableUIDocumentAfterDelay(0.2f)); // 200ms
                }
            }
        }

        private IEnumerator DisableUIDocumentAfterDelay(float delay)
        {
            yield return new WaitForSeconds(delay);
            Debug.Log("Disabling UIDocument.");
            MyPanelUIDocument.enabled = false;
        }

        public void ShowPanel()
        {
            MyPanelUIDocument.enabled = true;
            var panelElement = rootVisualElement.Q<VisualElement>("MyPanel");

            if (panelElement == null)
            {
                Debug.LogError("MyPanel not found.");
                return;
            }

            if (panelElement.ClassListContains("visible"))
            {
                Debug.LogWarning("Panel is already visible.");
                return;
            }

            panelElement.RemoveFromClassList("visible");
            StartCoroutine(AddVisibleClassWithDelay(panelElement, 0.01f));
        }

        private IEnumerator AddVisibleClassWithDelay(VisualElement panelElement, float delay)
        {
            yield return new WaitForSeconds(delay);

            Debug.Log("Adding 'visible' class to panel.");

            panelElement.AddToClassList("visible");
        }
    }

UIDocument component is initially disabled on game object. I have two buttons, first calls ShowPanel(), the second calls HidePanel(). I start the game, press the first button, the document component is enabled, the panel appears with a opacity animation, I press the second, the panel disappears with a opacity animation, the document component is disabled. If I press the first button again, the document component turns on, but there is no opacity animation. Same problem when using method panelElement.styleSheets.Add(MyVisibleStyleSheet); and separate style file MyVisibleStyleSheet.uss.

I also use coroutines because this method when called again, the UIDocument component cannot be disabled when re-enabled in the ShowPanel():

public void HidePanel()
{
    var panelElement = rootVisualElement.Q<VisualElement>("MyPanel");

    if (panelElement != null)
    {
        panelElement.RemoveFromClassList("visible");

        rootVisualElement.schedule.Execute(() =>
        {
            MyPanelUIDocument.enabled = false;
        }).ExecuteLater(200);
    }
}

Also there is some bug with MyPanelUIDocument.rootVisualElement. if I make any changes in the controller code, MyPanelUIDocument.rootVisualElement returns null on the first game launch after changing the code, if I re-launch the game without changes, rootVisualElement is not null.

private void OnEnable()
        {
            MyPanelUIDocument = GetComponent<UIDocument>();
            rootVisualElement = MyPanelUIDocument.rootVisualElement;

            MyButton = rootVisualElement.Q<Button>("MyButton");
        }

Unity 6000.0.27.

2

Instead of disabling UIDocument component I decided to use

UIDocument.rootVisualElement.style.display = DisplayStyle.Flex;

and

UIDocument.rootVisualElement.style.display = DisplayStyle.None;