broken

Runtime/Engine/Code/UI/UIDocumentView.cs

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+using System.Threading;
+using Cysharp.Threading.Tasks;
+using UnityEngine;
+using UnityEngine.Profiling;
+using UnityEngine.UIElements;
+using Logger = RebootKit.Engine.Foundation.Logger;
+
+namespace RebootKit.Engine.UI {
+    public abstract class UIDocumentView : MonoBehaviour, IView, IVisualElementBuilder {
+        static readonly Logger s_logger = new(nameof(UIDocumentView));
+
+        [SerializeField] UIDocument m_Document;
+
+        void OnEnable() {
+            s_logger.Debug("START");
+            Rebuild();
+        }
+
+        public async UniTask Show(CancellationToken cancellationToken) {
+            await UniTask.Yield(cancellationToken);
+        }
+
+        public async UniTask Hide(CancellationToken cancellationToken) {
+            await UniTask.Yield(cancellationToken);
+        }
+
+        protected void Rebuild() {
+            Profiler.BeginSample("UI Tree Build");
+            VisualElement child = Build();
+            Profiler.EndSample();
+
+            m_Document.rootVisualElement.Q<VisualElement>("root__container").Clear();
+            m_Document.rootVisualElement.Q<VisualElement>("root__container").Add(child);
+        }
+
+        public abstract VisualElement Build();
+    }
+}