feat: separate some Notification shared files.

src/Ursa/Controls/NotificationShared/WindowMessageManager.cs

@@ -0,0 +1,80 @@
+using System.Collections;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Metadata;
+using Avalonia.Controls.Primitives;
+using Avalonia.Layout;
+using Avalonia.VisualTree;
+
+namespace Ursa.Controls;
+
+/// <summary>
+/// An <see cref="WindowMessageManager"/> that displays messages in a <see cref="Window"/>.
+/// </summary>
+[TemplatePart(PART_Items, typeof(Panel))]
+public abstract class WindowMessageManager : TemplatedControl
+{
+    public const string PART_Items = "PART_Items";
+
+    protected IList? _items;
+
+    /// <summary>
+    /// Defines the <see cref="MaxItems"/> property.
+    /// </summary>
+    public static readonly StyledProperty<int> MaxItemsProperty =
+        AvaloniaProperty.Register<WindowMessageManager, int>(nameof(MaxItems), 5);
+
+    /// <summary>
+    /// Defines the maximum number of messages visible at once.
+    /// </summary>
+    public int MaxItems
+    {
+        get => GetValue(MaxItemsProperty);
+        set => SetValue(MaxItemsProperty, value);
+    }
+
+    static WindowMessageManager()
+    {
+        HorizontalAlignmentProperty.OverrideDefaultValue<WindowMessageManager>(HorizontalAlignment.Stretch);
+        VerticalAlignmentProperty.OverrideDefaultValue<WindowMessageManager>(VerticalAlignment.Stretch);
+    }
+
+    /// <inheritdoc/>
+    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+    {
+        base.OnApplyTemplate(e);
+
+        var itemsControl = e.NameScope.Find<Panel>(PART_Items);
+        _items = itemsControl?.Children;
+    }
+
+    public abstract void Show(object content);
+
+    /// <summary>
+    /// Installs the <see cref="WindowMessageManager"/> within the <see cref="AdornerLayer"/>
+    /// </summary>
+    protected void InstallFromTopLevel(TopLevel topLevel)
+    {
+        topLevel.TemplateApplied += TopLevelOnTemplateApplied;
+        var adorner = topLevel.FindDescendantOfType<VisualLayerManager>()?.AdornerLayer;
+        if (adorner is not null)
+        {
+            adorner.Children.Add(this);
+            AdornerLayer.SetAdornedElement(this, adorner);
+        }
+    }
+
+    protected void TopLevelOnTemplateApplied(object? sender, TemplateAppliedEventArgs e)
+    {
+        if (Parent is AdornerLayer adornerLayer)
+        {
+            adornerLayer.Children.Remove(this);
+            AdornerLayer.SetAdornedElement(this, null);
+        }
+
+        // Reinstall message manager on template reapplied.
+        var topLevel = (TopLevel)sender!;
+        topLevel.TemplateApplied -= TopLevelOnTemplateApplied;
+        InstallFromTopLevel(topLevel);
+    }
+}