Add some bubble notification animations + make IsClosing a direct property.

src/Avalonia.Controls/Notifications/Notification.cs

@@ -2,13 +2,14 @@
 using System.Reactive.Linq;
 using System.Threading.Tasks;
 using Avalonia.Controls.Primitives;
+using Avalonia.Data;
 using Avalonia.Interactivity;
 
 namespace Avalonia.Controls.Notifications
 {
     public class Notification : ContentControl
     {
-        private TimeSpan _closingAnimationTime = TimeSpan.Zero;
+        private TimeSpan _closingAnimationTime = TimeSpan.FromSeconds(0.25);
 
         static Notification()
         {
@@ -42,7 +43,19 @@ namespace Avalonia.Controls.Notifications
                 });
         }
 
-        public bool IsClosing { get; set; }
+        private bool _isClosing;
+
+        /// <summary>
+        /// Determines if the notification is already closing.
+        /// </summary>
+        public bool IsClosing
+        {
+            get { return _isClosing; }
+            private set { SetAndRaise(IsClosingProperty, ref _isClosing, value); }
+        }
+
+        public static readonly DirectProperty<Notification, bool> IsClosingProperty =
+            AvaloniaProperty.RegisterDirect<Notification, bool>(nameof(IsClosing), o => o.IsClosing);
 
         /// <summary>
         /// Defines the <see cref="NotificationCloseInvoked"/> event.

src/Avalonia.Themes.Default/NotificationArea.xaml

@@ -28,6 +28,34 @@
                 </Border>
             </ControlTemplate>
         </Setter>
+
+        <Style.Animations>
+          <Animation Duration="0:0:0.200" Easing="CubicEaseInOut">
+            <KeyFrame Cue="0%">
+              <Setter Property="Opacity" Value="0"/>
+              <Setter Property="TranslateTransform.X" Value="250"/>
+            </KeyFrame>
+            <KeyFrame Cue="100%">
+              <Setter Property="Opacity" Value="1"/>
+              <Setter Property="TranslateTransform.X" Value="0"/>
+            </KeyFrame>
+          </Animation>
+        </Style.Animations>
+    </Style>
+
+    <Style Selector="Notification[IsClosing=true]">
+        <Style.Animations>
+          <Animation Duration="0:0:0.150" Easing="CubicEaseInOut" FillMode="Forward">
+            <KeyFrame Cue="0%">             
+              <Setter Property="Opacity" Value="1"/>
+              <Setter Property="TranslateTransform.X" Value="0"/>
+            </KeyFrame>
+            <KeyFrame Cue="100%">
+              <Setter Property="Opacity" Value="0"/>
+              <Setter Property="TranslateTransform.X" Value="250"/>
+            </KeyFrame>
+          </Animation>
+        </Style.Animations>
     </Style>
 
     <Style Selector="Notification /template/ Button#PART_CloseButton">