Fix TopMost handling for Popups on Windows

samples/ControlCatalog/MainView.xaml

@@ -139,6 +139,9 @@
       <TabItem Header="Pointers">
         <pages:PointersPage />
       </TabItem>
+      <TabItem Header="Popups">
+        <pages:PopupsPage />
+      </TabItem>
       <TabItem Header="ProgressBar">
         <pages:ProgressBarPage />
       </TabItem>

samples/ControlCatalog/Pages/PopupsPage.xaml

@@ -0,0 +1,18 @@
+<UserControl x:Class="ControlCatalog.Pages.PopupsPage"
+             xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+
+  <StackPanel Orientation="Vertical" Spacing="10">
+
+    <TextBlock Text="'Light Dismiss' Popup" />
+    <Button Content="Show Popup" Click="ButtonLightDismiss_OnClick" />
+
+    <TextBlock Text="Popup that stays open" />
+    <Button Content="Show Popup" Click="ButtonPopupStaysOpen_OnClick" />
+
+    <TextBlock Text="TopMost popup that stays open" />
+    <Button Content="Show Popup" Click="ButtonTopMostPopupStaysOpen" />
+
+  </StackPanel>
+
+</UserControl>

samples/ControlCatalog/Pages/PopupsPage.xaml.cs

@@ -0,0 +1,111 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Controls.Primitives.PopupPositioning;
+using Avalonia.Interactivity;
+using Avalonia.Layout;
+using Avalonia.Markup.Xaml;
+using Avalonia.Media;
+
+namespace ControlCatalog.Pages;
+
+public class PopupsPage : UserControl
+{
+    private Popup? _popup;
+    private Popup? _topMostPopup;
+    public PopupsPage()
+    {
+        InitializeComponent();
+
+    }
+
+    private void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    private void ButtonLightDismiss_OnClick(object sender, RoutedEventArgs e)
+    {
+        new Popup
+        {
+            Placement = PlacementMode.Bottom,
+            PlacementTarget = sender as Button,
+            Child = new Panel { Margin = new Thickness(10) ,Children = { new TextBlock { Text = "Popup Content" } }},
+            IsLightDismissEnabled = true,
+            IsOpen = true
+        };
+    }
+
+    private void ButtonPopupStaysOpen_OnClick(object sender, RoutedEventArgs e)
+    {
+        if (_popup is not null)
+            return;
+
+        var closeButton = new Button { Content = "Click to Close" };
+        closeButton.Click += (o, args) =>
+        {
+            if (_popup is null)
+                return;
+
+            LogicalChildren.Remove(_popup);
+            _popup.IsOpen = false;
+            _popup = null;
+        };
+        _popup = new Popup
+        {
+            Placement = PlacementMode.Bottom,
+            PlacementTarget = sender as Button,
+            Child = new StackPanel
+            {
+                Spacing = 10,
+                Margin = new Thickness(10),
+                Orientation = Orientation.Vertical,
+                Children =
+                {
+                    new TextBox
+                    {
+                        Width = 100,
+                        Text = "Some text", 
+                    }, 
+                    new TextBox
+                    {
+                        Width = 100,
+                        Text = "Some other text", 
+                    }, 
+                    closeButton
+                }
+            },
+            IsLightDismissEnabled = false,
+        };
+
+        LogicalChildren.Add(_popup);
+        _popup.IsOpen = true;
+    }
+
+    private void ButtonTopMostPopupStaysOpen(object sender, RoutedEventArgs e)
+    {
+        if (_topMostPopup is not null)
+            return;
+
+        var closeButton = new Button { Content = "Click to Close" };
+        closeButton.Click += (o, args) =>
+        {
+            if (_topMostPopup is null)
+                return;
+            _topMostPopup.IsOpen = false;
+            _topMostPopup = null;
+        };
+        _topMostPopup = new Popup
+        {
+            Placement = PlacementMode.Bottom,
+            PlacementTarget = sender as Button,
+            Child = new Panel
+            {
+                Margin = new Thickness(10), Children = { closeButton }
+            },
+            IsLightDismissEnabled = false,
+            Topmost = true,
+            IsOpen = true
+        };
+    }
+}

src/Avalonia.Controls/Primitives/PopupRoot.cs

@@ -61,6 +61,7 @@ public PopupRoot(TopLevel parent, IPopupImpl impl, IAvaloniaDependencyResolver?
         {
             ParentTopLevel = parent;
             impl.SetWindowManagerAddShadowHint(WindowManagerAddShadowHint);
+            impl.SetTopmost(Topmost);
         }
 
         /// <summary>
@@ -225,6 +226,10 @@ protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs chang
             {
                 PlatformImpl?.SetWindowManagerAddShadowHint(change.GetNewValue<bool>());
             }
+            else if (change.Property == TopmostProperty)
+            {
+                PlatformImpl?.SetTopmost(Topmost);
+            }
         }
     }
 }

src/Windows/Avalonia.Win32/PopupImpl.cs

@@ -53,8 +53,7 @@ protected override IntPtr CreateWindowOverride(ushort atom)
                 UnmanagedMethods.WindowStyles.WS_CLIPCHILDREN;
 
             UnmanagedMethods.WindowStyles exStyle =
-                UnmanagedMethods.WindowStyles.WS_EX_TOOLWINDOW |
-                UnmanagedMethods.WindowStyles.WS_EX_TOPMOST;
+                UnmanagedMethods.WindowStyles.WS_EX_TOOLWINDOW;
 
             var result = UnmanagedMethods.CreateWindowEx(
                 (int)exStyle,
@@ -84,6 +83,10 @@ protected override IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr l
                     _maxAutoSize = null;
                     goto default;
                 case UnmanagedMethods.WindowsMessage.WM_MOUSEACTIVATE:
+                    if (_parent?.Handle is not null)
+                    {
+                        UnmanagedMethods.SetFocus(_parent.Handle.Handle);
+                    }
                     return (IntPtr)UnmanagedMethods.MouseActivate.MA_NOACTIVATE;
                 default:
                     return base.WndProc(hWnd, msg, wParam, lParam);