Add a CompositeTransition

src/Avalonia.Visuals/Animation/CompositeTransition.cs

@@ -0,0 +1,61 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Avalonia.Metadata;
+
+namespace Avalonia.Animation
+{
+    /// <summary>
+    /// Defines a composite transition that can be used to combine multiple transitions into one.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// Instantiate the <see cref="CompositeTransition" /> in XAML and initialize the
+    /// <see cref="Transitions" /> property in order to have many animations triggered at once.
+    /// For example, you can combine <see cref="CrossFade"/> and <see cref="PageSlide"/>.
+    /// <code>
+    /// <![CDATA[
+    /// <reactiveUi:RoutedViewHost Router="{Binding Router}">
+    ///   <reactiveUi:RoutedViewHost.PageTransition>
+    ///     <CompositeTransition>
+    ///       <PageSlide Duration="0.5" />
+    ///       <CrossFade Duration="0.5" />
+    ///     </CompositeTransition>
+    ///   </reactiveUi:RoutedViewHost.PageTransition>
+    /// </reactiveUi:RoutedViewHost>
+    /// ]]>
+    /// </code>
+    /// </para>
+    /// </remarks>
+    public class CompositeTransition : IPageTransition
+    {
+        /// <summary>
+        /// Gets or sets the transitions to be executed. Can be defined from XAML.
+        /// </summary>
+        [Content]
+        public List<IPageTransition> Transitions { get; set; } = new List<IPageTransition>();
+
+        /// <summary>
+        /// Starts the animation.
+        /// </summary>
+        /// <param name="from">
+        /// The control that is being transitioned away from. May be null.
+        /// </param>
+        /// <param name="to">
+        /// The control that is being transitioned to. May be null.
+        /// </param>
+        /// <param name="forward">
+        /// Defines the direction of the transition.
+        /// </param>
+        /// <returns>
+        /// A <see cref="Task"/> that tracks the progress of the animation.
+        /// </returns>
+        public Task Start(Visual from, Visual to, bool forward)
+        {
+            var transitionTasks = Transitions
+                .Select(transition => transition.Start(from, to, forward))
+                .ToList();
+            return Task.WhenAll(transitionTasks);
+        }
+    }
+}