Detach all styles when a style is removed from a control.

src/Avalonia.Styling/Styling/IStyle.cs

@@ -18,5 +18,7 @@ namespace Avalonia.Styling
         /// The control that contains this style. May be null.
         /// </param>
         void Attach(IStyleable control, IStyleHost container);
+
+        void Detach();
     }
 }

src/Avalonia.Styling/Styling/Style.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Reactive.Disposables;
 using System.Reactive.Linq;
 using Avalonia.Animation;
 using Avalonia.Controls;
@@ -15,9 +16,12 @@ namespace Avalonia.Styling
     /// </summary>
     public class Style : AvaloniaObject, IStyle, ISetStyleParent
     {
-        private static Dictionary<IStyleable, List<IDisposable>> _applied =
-            new Dictionary<IStyleable, List<IDisposable>>();
+        private static Dictionary<IStyleable, CompositeDisposable> _applied =
+            new Dictionary<IStyleable, CompositeDisposable>();
         private IResourceNode _parent;
+
+        private CompositeDisposable _subscriptions;
+
         private IResourceDictionary _resources;
 
         private IList<IAnimation> _animations;
@@ -88,6 +92,14 @@ namespace Avalonia.Styling
             }
         }
 
+        private CompositeDisposable Subscriptions
+        {
+            get
+            {
+                return _subscriptions ?? (_subscriptions = new CompositeDisposable(2));
+            }
+        }
+
         /// <inheritdoc/>
         IResourceNode IResourceNode.ResourceParent => _parent;
 
@@ -109,7 +121,9 @@ namespace Avalonia.Styling
 
                 if (match.ImmediateResult != false)
                 {
-                    var subs = GetSubscriptions(control);
+                    var controlSubscriptions = GetSubscriptions(control);
+                    
+                    var subs = new CompositeDisposable(Setters.Count + Animations.Count);
 
                     foreach (var animation in Animations)
                     {
@@ -129,17 +143,25 @@ namespace Avalonia.Styling
                         var sub = setter.Apply(this, control, match.ObservableResult);
                         subs.Add(sub);
                     }
+
+                    controlSubscriptions.Add(subs);
+                    Subscriptions.Add(subs);
                 }
             }
             else if (control == container)
             {
-                var subs = GetSubscriptions(control);
+                var controlSubscriptions = GetSubscriptions(control);
+
+                var subs = new CompositeDisposable(Setters.Count);
 
                 foreach (var setter in Setters)
                 {
                     var sub = setter.Apply(this, control, null);
                     subs.Add(sub);
                 }
+                
+                controlSubscriptions.Add(subs);
+                Subscriptions.Add(subs);
             }
         }
 
@@ -180,16 +202,25 @@ namespace Avalonia.Styling
                 throw new InvalidOperationException("The Style already has a parent.");
             }
 
+            if (parent == null)
+            {
+                Detach();
+            }
+
             _parent = parent;
         }
 
-        private static List<IDisposable> GetSubscriptions(IStyleable control)
+        public void Detach()
         {
-            List<IDisposable> subscriptions;
+            _subscriptions?.Dispose();
+            _subscriptions = null;
+        }
 
-            if (!_applied.TryGetValue(control, out subscriptions))
+        private static CompositeDisposable GetSubscriptions(IStyleable control)
+        {
+            if (!_applied.TryGetValue(control, out var subscriptions))
             {
-                subscriptions = new List<IDisposable>(2);
+                subscriptions = new CompositeDisposable(2);
                 subscriptions.Add(control.StyleDetach.Subscribe(ControlDetach));
                 _applied.Add(control, subscriptions);
             }
@@ -206,10 +237,7 @@ namespace Avalonia.Styling
         {
             var subscriptions = _applied[control];
 
-            foreach (var subscription in subscriptions)
-            {
-                subscription.Dispose();
-            }
+            subscriptions.Dispose();
 
             _applied.Remove(control);
         }

src/Avalonia.Styling/Styling/Styles.cs

@@ -105,6 +105,14 @@ namespace Avalonia.Styling
             }
         }
 
+        public void Detach()
+        {
+            foreach (IStyle style in this)
+            {
+                style.Detach();
+            }
+        }
+
         /// <inheritdoc/>
         public bool TryGetResource(string key, out object value)
         {

src/Avalonia.Styling/Styling/packages.config

@@ -1,9 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<packages>
-  <package id="Rx-Core" version="2.2.5" targetFramework="portable-net45+win8" userInstalled="true" />
-  <package id="Rx-Interfaces" version="2.2.5" targetFramework="portable-net45+win8" userInstalled="true" />
-  <package id="Rx-Linq" version="2.2.5" targetFramework="portable-net45+win8" userInstalled="true" />
-  <package id="Rx-Main" version="2.2.5" targetFramework="portable-net45+win8" userInstalled="true" />
-  <package id="Rx-PlatformServices" version="2.2.5" targetFramework="portable-net45+win8" userInstalled="true" />
-  <package id="Splat" version="1.6.2" targetFramework="portable45-net45+win8" userInstalled="true" />
-</packages>

src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs

@@ -70,6 +70,14 @@ namespace Avalonia.Markup.Xaml.Styling
             }
         }
 
+        public void Detach()
+        {
+            if (Source != null)
+            {
+                Loaded.Detach();
+            }
+        }
+
         /// <inheritdoc/>
         public bool TryGetResource(string key, out object value) => Loaded.TryGetResource(key, out value);
 
@@ -90,4 +98,4 @@ namespace Avalonia.Markup.Xaml.Styling
             _parent = parent;
         }
     }
-}
+}

tests/Avalonia.Styling.UnitTests/StyleTests.cs

@@ -167,6 +167,31 @@ namespace Avalonia.Styling.UnitTests
             Assert.Equal(new Thickness(0), border.BorderThickness);
         }
 
+        [Fact]
+        public void Style_Should_Detach_Setters_When_Detach_Is_Called()
+        {
+            Border border;
+
+            var style = new Style(x => x.OfType<Border>())
+            {
+                Setters = new[]
+                {
+                    new Setter(Border.BorderThicknessProperty, new Thickness(4)),
+                }
+            };
+
+            var root = new TestRoot
+            {
+                Child = border = new Border(),
+            };
+
+            style.Attach(border, null);
+
+            Assert.Equal(new Thickness(4), border.BorderThickness);
+            style.Detach();
+            Assert.Equal(new Thickness(0), border.BorderThickness);
+        }
+
         private class Class1 : Control
         {
             public static readonly StyledProperty<string> FooProperty =