Fix window Loaded and Unloaded events

src/Avalonia.Controls/Control.cs

@@ -8,6 +8,7 @@ using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.Interactivity;
+using Avalonia.LogicalTree;
 using Avalonia.Media;
 using Avalonia.Rendering;
 using Avalonia.Styling;
@@ -104,7 +105,6 @@ namespace Avalonia.Controls
         private static readonly HashSet<Control> _loadedQueue = new HashSet<Control>();
         private static readonly HashSet<Control> _loadedProcessingQueue = new HashSet<Control>();
 
-        private bool _isAttachedToVisualTree = false;
         private bool _isLoaded = false;
         private DataTemplates? _dataTemplates;
         private IControl? _focusAdorner;
@@ -344,10 +344,10 @@ namespace Avalonia.Controls
         /// Invoked as the first step of marking the control as loaded and raising the
         /// <see cref="Loaded"/> event.
         /// </summary>
-        internal void OnLoadedCore()
+        internal virtual void OnLoadedCore()
         {
             if (_isLoaded == false &&
-                _isAttachedToVisualTree)
+                ((ILogical)this).IsAttachedToLogicalTree)
             {
                 _isLoaded = true;
                 OnLoaded();
@@ -395,7 +395,6 @@ namespace Avalonia.Controls
         protected sealed override void OnAttachedToVisualTreeCore(VisualTreeAttachmentEventArgs e)
         {
             base.OnAttachedToVisualTreeCore(e);
-            _isAttachedToVisualTree = true;
 
             InitializeIfNeeded();
 
@@ -406,7 +405,6 @@ namespace Avalonia.Controls
         protected sealed override void OnDetachedFromVisualTreeCore(VisualTreeAttachmentEventArgs e)
         {
             base.OnDetachedFromVisualTreeCore(e);
-            _isAttachedToVisualTree = false;
 
             OnUnloadedCore();
         }

tests/Avalonia.Controls.UnitTests/LoadedTests.cs

@@ -0,0 +1,71 @@
+using Avalonia.Platform;
+using Avalonia.Threading;
+using Avalonia.UnitTests;
+using Moq;
+using Xunit;
+
+namespace Avalonia.Controls.UnitTests;
+
+public class LoadedTests
+{
+    [Fact]
+    public void Window_Loads_And_Unloads()
+    {
+        using (UnitTestApplication.Start(TestServices.StyledWindow))
+        {
+            int loadedCount = 0, unloadedCount = 0;
+            var target = new Window();
+
+            target.Loaded += (_, _) => loadedCount++;
+            target.Unloaded += (_, _) => unloadedCount++; 
+            
+            Assert.Equal(0, loadedCount);
+            Assert.Equal(0, unloadedCount);
+            
+            target.Show();
+            Dispatcher.UIThread.RunJobs(DispatcherPriority.Loaded);
+            Assert.True(target.IsLoaded);
+
+            Assert.Equal(1, loadedCount);
+            Assert.Equal(0, unloadedCount);
+            
+            target.Close();
+            
+            Assert.Equal(1, loadedCount);
+            Assert.Equal(1, unloadedCount);
+            Assert.False(target.IsLoaded);
+        }
+    }
+    
+    [Fact]
+    public void Control_Loads_And_Unloads()
+    {
+        using (UnitTestApplication.Start(TestServices.StyledWindow))
+        {
+            int loadedCount = 0, unloadedCount = 0;
+            var window = new Window();
+            window.Show();
+
+            var target = new Button();
+
+            target.Loaded += (_, _) => loadedCount++;
+            target.Unloaded += (_, _) => unloadedCount++; 
+            
+            Assert.Equal(0, loadedCount);
+            Assert.Equal(0, unloadedCount);
+            
+            window.Content = target;
+            Dispatcher.UIThread.RunJobs(DispatcherPriority.Loaded);
+            Assert.True(target.IsLoaded);
+
+            Assert.Equal(1, loadedCount);
+            Assert.Equal(0, unloadedCount);
+            
+            window.Content = null;
+            
+            Assert.Equal(1, loadedCount);
+            Assert.Equal(1, unloadedCount);
+            Assert.False(target.IsLoaded);
+        }
+    }
+}