Merge Common to Desktop

app/InkForge.Desktop/Services/TopLevels.cs

@@ -0,0 +1,54 @@
+using Avalonia;
+using Avalonia.Controls;
+
+namespace InkForge.Desktop.Services;
+
+public class TopLevels
+{
+	public static readonly AttachedProperty<object?> RegisterProperty
+		= AvaloniaProperty.RegisterAttached<TopLevels, Visual, object?>("Register");
+
+	private static readonly Dictionary<object, Visual> RegistrationMapper = [];
+
+	static TopLevels()
+	{
+		RegisterProperty.Changed.AddClassHandler<Visual>(RegisterChanged);
+	}
+
+	public static object? GetRegister(AvaloniaObject element)
+	{
+		return element.GetValue(RegisterProperty);
+	}
+
+	public static TopLevel? GetTopLevelForContext(object context)
+	{
+		return TopLevel.GetTopLevel(GetVisualForContext(context));
+	}
+
+	public static Visual? GetVisualForContext(object context)
+	{
+		return RegistrationMapper.TryGetValue(context, out var result) ? result : null;
+	}
+
+	public static void SetRegister(AvaloniaObject element, object value)
+	{
+		element.SetValue(RegisterProperty, value);
+	}
+
+	private static void RegisterChanged(Visual sender, AvaloniaPropertyChangedEventArgs e)
+	{
+		ArgumentNullException.ThrowIfNull(sender);
+
+		// Unregister any old registered context
+		if (e.OldValue != null)
+		{
+			RegistrationMapper.Remove(e.OldValue);
+		}
+
+		// Register any new context
+		if (e.NewValue != null)
+		{
+			RegistrationMapper.Add(e.NewValue, sender);
+		}
+	}
+}