feat: add a property to show if there is modal dialog available in a host.

demo/Ursa.Demo/Views/MainView.axaml

@@ -16,8 +16,16 @@
     <Design.DataContext>
         <vm:MainViewViewModel />
     </Design.DataContext>
-
+    <Panel>
-    <Grid ColumnDefinitions="Auto, *" RowDefinitions="Auto, *">
+        <Grid
+            Classes.Blur="{Binding #host.HasModal}"
+            ColumnDefinitions="Auto, *"
+            RowDefinitions="Auto, *">
+            <Grid.Styles>
+                <Style Selector="Grid.Blur">
+                    <Setter Property="Effect" Value="blur(20)" />
+                </Style>
+            </Grid.Styles>
             <Border
                 Grid.RowSpan="2"
                 Padding="8,4"
@@ -90,7 +98,7 @@
                     <converters:ViewLocator />
                 </ContentControl.ContentTemplate>
             </ContentControl>
-        <u:OverlayDialogHost Grid.Row="0" Grid.Column="0" Grid.RowSpan="2" Grid.ColumnSpan="2" SnapThickness="20"/>
         </Grid>
-
+        <u:OverlayDialogHost Name="host" SnapThickness="20" />
+    </Panel>
 </UserControl>

src/Ursa/Controls/OverlayShared/OverlayDialogHost.Dialog.cs

@@ -92,7 +92,7 @@ public partial class OverlayDialogHost
             Children.Add(mask);
         }
         this.Children.Add(control);
-        _layers.Add(new DialogPair(mask, control));
+        _layers.Add(new DialogPair(mask, control, false));
         control.Measure(this.Bounds.Size);
         control.Arrange(new Rect(control.DesiredSize));
         SetToPosition(control);
@@ -118,6 +118,11 @@ public partial class OverlayDialogHost
             {
                 await _maskDisappearAnimation.RunAsync(layer.Mask);
                 Children.Remove(layer.Mask);
+                if (layer.Modal)
+                {
+                    _modalCount--;
+                    HasModal = _modalCount > 0;
+                }
             }
             
             ResetZIndices();
@@ -142,6 +147,8 @@ public partial class OverlayDialogHost
         control.AddHandler(OverlayFeedbackElement.ClosedEvent, OnDialogControlClosing);
         control.AddHandler(DialogControlBase.LayerChangedEvent, OnDialogLayerChanged);
         _maskAppearAnimation.RunAsync(mask);
+        _modalCount++;
+        HasModal = _modalCount > 0;
         control.IsClosed = false;
     }
 

src/Ursa/Controls/OverlayShared/OverlayDialogHost.Shared.cs

@@ -24,14 +24,29 @@ public partial class OverlayDialogHost: Canvas
     {
         internal PureRectangle? Mask;
         internal OverlayFeedbackElement Element;
+        internal bool Modal;
 
-        public DialogPair(PureRectangle? mask, OverlayFeedbackElement element)
+        public DialogPair(PureRectangle? mask, OverlayFeedbackElement element, bool modal = true)
         {
             Mask = mask;
             Element = element;
+            Modal = modal;
         }
     }
 
+    private int _modalCount = 0;
+    
+    
+
+    public static readonly DirectProperty<OverlayDialogHost, bool> HasModalProperty = AvaloniaProperty.RegisterDirect<OverlayDialogHost, bool>(
+        nameof(HasModal), o => o.HasModal);
+    private bool _hasModal;
+    public bool HasModal
+    {
+        get => _hasModal;
+        private set => SetAndRaise(HasModalProperty, ref _hasModal, value);
+    }
+    
     static OverlayDialogHost()
     {
         ClipToBoundsProperty.OverrideDefaultValue<OverlayDialogHost>(true);