From fb9e75c6e4a31135c573474c4c319d2734bb7ebd Mon Sep 17 00:00:00 2001
From: Yimeng Wu <me@kinnara.cn>
Date: Mon, 20 Apr 2020 01:59:09 +0800
Subject: [PATCH] Make SplitView transitions smoother

---
 ModernWpf.Controls/SplitView/SplitView.cs     |  1 +
 .../HamburgerMenu/HamburgerMenuEx.cs          | 11 +----
 ModernWpf/Helpers/AnimationHelper.cs          | 47 +++++++++++++++++++
 ModernWpf/Properties/AssemblyInfo.cs          |  1 +
 4 files changed, 50 insertions(+), 10 deletions(-)
 create mode 100644 ModernWpf/Helpers/AnimationHelper.cs

diff --git a/ModernWpf.Controls/SplitView/SplitView.cs b/ModernWpf.Controls/SplitView/SplitView.cs
index f9c75a74..5c38d138 100644
--- a/ModernWpf.Controls/SplitView/SplitView.cs
+++ b/ModernWpf.Controls/SplitView/SplitView.cs
@@ -58,6 +58,7 @@ public override void OnApplyTemplate()
             {
                 _displayModeStates.CurrentStateChanging += OnDisplayModeStatesCurrentStateChanging;
                 _displayModeStates.CurrentStateChanged += OnDisplayModeStatesCurrentStateChanged;
+                AnimationHelper.DeferTransitions(_displayModeStates);
             }
 
             UpdateTemplateSettings();
diff --git a/ModernWpf.MahApps/HamburgerMenu/HamburgerMenuEx.cs b/ModernWpf.MahApps/HamburgerMenu/HamburgerMenuEx.cs
index d941e186..50b309bd 100644
--- a/ModernWpf.MahApps/HamburgerMenu/HamburgerMenuEx.cs
+++ b/ModernWpf.MahApps/HamburgerMenu/HamburgerMenuEx.cs
@@ -11,7 +11,6 @@
 using System.Windows.Media;
 using System.Windows.Media.Animation;
 using System.Windows.Shapes;
-using System.Windows.Threading;
 using SplitView = MahApps.Metro.Controls.SplitView;
 using SplitViewDisplayMode = MahApps.Metro.Controls.SplitViewDisplayMode;
 
@@ -788,16 +787,8 @@ private void PlayIndicatorAnimations(UIElement indicator, double from, double to
 
             var indicatorAsFE = (FrameworkElement)indicator;
             SetElementAnimation(indicatorAsFE, storyboard);
+            AnimationHelper.DeferBegin(storyboard);
             storyboard.Begin(indicatorAsFE, true);
-            storyboard.Pause(indicatorAsFE);
-            Dispatcher.BeginInvoke(() =>
-            {
-                var animation = GetElementAnimation(indicatorAsFE);
-                if (animation == storyboard)
-                {
-                    animation.Resume(indicatorAsFE);
-                }
-            }, DispatcherPriority.Render);
         }
 
         private void OnAnimationComplete()
diff --git a/ModernWpf/Helpers/AnimationHelper.cs b/ModernWpf/Helpers/AnimationHelper.cs
new file mode 100644
index 00000000..a6e0d261
--- /dev/null
+++ b/ModernWpf/Helpers/AnimationHelper.cs
@@ -0,0 +1,47 @@
+using System;
+using System.Diagnostics;
+using System.Windows;
+using System.Windows.Media.Animation;
+using System.Windows.Threading;
+
+namespace ModernWpf
+{
+    internal static class AnimationHelper
+    {
+        public static void DeferBegin(Storyboard storyboard)
+        {
+            storyboard.CurrentStateInvalidated += OnStoryboardCurrentStateInvalidated;
+
+            static void OnStoryboardCurrentStateInvalidated(object sender, EventArgs e)
+            {
+                if (sender is ClockGroup clock &&
+                    clock.HasControllableRoot &&
+                    clock.CurrentState == ClockState.Active &&
+                    !clock.IsPaused)
+                {
+                    clock.Controller.Pause();
+                    clock.Dispatcher.BeginInvoke(() =>
+                    {
+                        Debug.Assert(clock.IsPaused || clock.CurrentState != ClockState.Active);
+                        if (clock.IsPaused)
+                        {
+                            clock.Controller.Resume();
+                        }
+                    }, DispatcherPriority.Loaded);
+                }
+            }
+        }
+
+        public static void DeferTransitions(VisualStateGroup group)
+        {
+            foreach (VisualTransition transition in group.Transitions)
+            {
+                var storyboard = transition.Storyboard;
+                if (storyboard != null)
+                {
+                    DeferBegin(storyboard);
+                }
+            }
+        }
+    }
+}
diff --git a/ModernWpf/Properties/AssemblyInfo.cs b/ModernWpf/Properties/AssemblyInfo.cs
index 1c63404d..efcb596b 100644
--- a/ModernWpf/Properties/AssemblyInfo.cs
+++ b/ModernWpf/Properties/AssemblyInfo.cs
@@ -12,6 +12,7 @@
 )]
 
 [assembly: InternalsVisibleTo("ModernWpf.Controls")]
+[assembly: InternalsVisibleTo("ModernWpf.MahApps")]
 
 [assembly: XmlnsPrefix("http://schemas.modernwpf.com/2019", "ui")]
 [assembly: XmlnsDefinition("http://schemas.modernwpf.com/2019", "ModernWpf")]