refactor(ui): own retained controller lifetimes

src/AcDream.App/UI/RetainedPanelControllerGroup.cs

@@ -0,0 +1,52 @@
+using System;
+
+namespace AcDream.App.UI;
+
+/// <summary>
+/// Gives one retained window a single lifecycle owner when its imported subtree
+/// is bound by multiple focused controllers (for example toolbar+selection or
+/// inventory+paperdoll). Teardown runs in reverse construction order and is
+/// idempotent.
+/// </summary>
+public sealed class RetainedPanelControllerGroup : IRetainedPanelController
+{
+    private readonly IRetainedPanelController[] _controllers;
+    private bool _disposed;
+
+    public RetainedPanelControllerGroup(params IRetainedPanelController[] controllers)
+    {
+        ArgumentNullException.ThrowIfNull(controllers);
+        _controllers = (IRetainedPanelController[])controllers.Clone();
+        for (int i = 0; i < _controllers.Length; i++)
+            ArgumentNullException.ThrowIfNull(_controllers[i]);
+    }
+
+    public void OnShown()
+    {
+        if (_disposed) return;
+        for (int i = 0; i < _controllers.Length; i++)
+            _controllers[i].OnShown();
+    }
+
+    public void OnHidden()
+    {
+        if (_disposed) return;
+        for (int i = _controllers.Length - 1; i >= 0; i--)
+            _controllers[i].OnHidden();
+    }
+
+    public void OnDescendantFocusChanged(UiElement? focusedDescendant)
+    {
+        if (_disposed) return;
+        for (int i = 0; i < _controllers.Length; i++)
+            _controllers[i].OnDescendantFocusChanged(focusedDescendant);
+    }
+
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        for (int i = _controllers.Length - 1; i >= 0; i--)
+            _controllers[i].Dispose();
+    }
+}