Defer style changes when changing classes.

Because we don't know which style to apply until all selectors have
received notification of a class change.

Perspex.UnitTests/Styling/SubscribeCheck.cs

@@ -27,11 +27,11 @@ namespace Perspex.UnitTests.Styling
     {
         public SubscribeCheck()
         {
-            this.Classes = new PerspexList<string>();
+            this.Classes = Classes;
             this.SubscribeCheckObservable = new TestObservable();
         }
 
-        public PerspexList<string> Classes
+        public Classes Classes
         {
             get;
             private set;

Perspex/Classes.cs

@@ -0,0 +1,172 @@
+// -----------------------------------------------------------------------
+// <copyright file="Classes.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+    using System.Collections.Specialized;
+    using System.Linq;
+    using System.Reactive;
+    using System.Reactive.Subjects;
+
+    public class Classes : ICollection<string>, INotifyCollectionChanged
+    {
+        private List<string> inner;
+
+        private Subject<NotifyCollectionChangedEventArgs> beforeChanged
+            = new Subject<NotifyCollectionChangedEventArgs>();
+
+        private Subject<NotifyCollectionChangedEventArgs> changed
+            = new Subject<NotifyCollectionChangedEventArgs>();
+
+        private Subject<NotifyCollectionChangedEventArgs> afterChanged
+            = new Subject<NotifyCollectionChangedEventArgs>();
+
+        public Classes()
+        {
+            this.inner = new List<string>();
+        }
+
+        public Classes(params string[] classes)
+        {
+            this.inner = new List<string>(classes);
+        }
+
+        public Classes(IEnumerable<string> classes)
+        {
+            this.inner = new List<string>(classes);
+        }
+
+        public event NotifyCollectionChangedEventHandler CollectionChanged;
+
+        public int Count
+        {
+            get { return this.inner.Count; }
+        }
+
+        public bool IsReadOnly
+        {
+            get { return false; }
+        }
+
+        public IObservable<NotifyCollectionChangedEventArgs> BeforeChanged
+        {
+            get { return this.beforeChanged; }
+        }
+
+        public IObservable<NotifyCollectionChangedEventArgs> Changed
+        {
+            get { return this.changed; }
+        }
+
+        public IObservable<NotifyCollectionChangedEventArgs> AfterChanged
+        {
+            get { return this.afterChanged; }
+        }
+
+        public void Add(string item)
+        {
+            this.Add(Enumerable.Repeat(item, 1));
+        }
+
+        public void Add(params string[] items)
+        {
+            this.Add((IEnumerable<string>)items);
+        }
+
+        public void Add(IEnumerable<string> items)
+        {
+            items = items.Except(this.inner);
+
+            NotifyCollectionChangedEventArgs e = new NotifyCollectionChangedEventArgs(
+                NotifyCollectionChangedAction.Add,
+                items);
+
+            this.beforeChanged.OnNext(e);
+            this.inner.AddRange(items);
+            this.RaiseChanged(e);
+        }
+
+        private void RaiseChanged(NotifyCollectionChangedEventArgs e)
+        {
+            if (this.CollectionChanged != null)
+            {
+                this.CollectionChanged(this, e);
+            }
+
+            this.changed.OnNext(e);
+            this.afterChanged.OnNext(e);
+        }
+
+        public void Clear()
+        {
+            NotifyCollectionChangedEventArgs e = new NotifyCollectionChangedEventArgs(
+                NotifyCollectionChangedAction.Reset);
+
+            this.beforeChanged.OnNext(e);
+            this.inner.Clear();
+            this.RaiseChanged(e);
+        }
+
+        public bool Contains(string item)
+        {
+            return this.inner.Contains(item);
+        }
+
+        public void CopyTo(string[] array, int arrayIndex)
+        {
+            this.inner.CopyTo(array, arrayIndex);
+        }
+
+        public IEnumerator<string> GetEnumerator()
+        {
+            return inner.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return inner.GetEnumerator();
+        }
+
+        public bool Remove(string item)
+        {
+            return this.Remove(Enumerable.Repeat(item, 1));
+        }
+
+        public bool Remove(params string[] items)
+        {
+            return this.Remove((IEnumerable<string>)items);
+        }
+
+        public bool Remove(IEnumerable<string> items)
+        {
+            items = items.Intersect(this.inner);
+
+            if (items.Any())
+            {
+                NotifyCollectionChangedEventArgs e = new NotifyCollectionChangedEventArgs(
+                    NotifyCollectionChangedAction.Remove,
+                    items);
+
+                this.beforeChanged.OnNext(e);
+
+                foreach (string item in items)
+                {
+                    this.inner.Remove(item);
+                }
+
+                this.RaiseChanged(e);
+                return true;
+            }
+            else
+            {
+                return false;
+            }
+        }
+    }
+}

Perspex/Controls/Control.cs

@@ -74,7 +74,10 @@ namespace Perspex.Controls
 
         public Control()
         {
-            this.Classes = new PerspexList<string>();
+            this.Classes = new Classes();
+            this.Classes.BeforeChanged.Subscribe(x => this.BeginDeferStyleChanges());
+            this.Classes.AfterChanged.Subscribe(x => this.EndDeferStyleChanges());
+
             this.GetObservableWithHistory(ParentPropertyRW).Subscribe(this.ParentChanged);
 
             this.GetObservable(IsMouseOverProperty).Subscribe(x =>
@@ -140,7 +143,7 @@ namespace Perspex.Controls
             set { this.SetValue(BorderThicknessProperty, value); }
         }
 
-        public PerspexList<string> Classes
+        public Classes Classes
         {
             get;
             private set;

Perspex/Perspex.csproj

@@ -69,6 +69,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Application.cs" />
+    <Compile Include="Classes.cs" />
     <Compile Include="Controls\Border.cs" />
     <Compile Include="Controls\Button.cs" />
     <Compile Include="Controls\ContentPresenter.cs" />

Perspex/PerspexObject.cs

@@ -12,6 +12,7 @@ namespace Perspex
     using System.Linq;
     using System.Linq.Expressions;
     using System.Reactive;
+    using System.Reactive.Disposables;
     using System.Reactive.Linq;
     using System.Reflection;
     using Splat;
@@ -94,6 +95,40 @@ namespace Perspex
             }
         }
 
+        /// <summary>
+        /// Defers property updates due to style changes until <see cref="EndDeferStyleChanges"/>
+        /// is called.
+        /// </summary>
+        public void BeginDeferStyleChanges()
+        {
+            foreach (PriorityValue v in this.values.Values)
+            {
+                v.BeginDeferStyleChanges();
+            }
+
+            this.Log().Debug(string.Format(
+                "Defer style changes on {0} (#{1:x8})",
+                this.GetType().Name,
+                this.GetHashCode()));
+        }
+
+        /// <summary>
+        /// Ends the defer of property updates due to style changes initiated by a previous call 
+        /// to <see cref="BeginDeferStyleChanges"/>.
+        /// </summary>
+        public void EndDeferStyleChanges()
+        {
+            foreach (PriorityValue v in this.values.Values)
+            {
+                v.EndDeferStyleChanges();
+            }
+
+            this.Log().Debug(string.Format(
+                "End defer style changes on {0} (#{1:x8})",
+                this.GetType().Name,
+                this.GetHashCode()));
+        }
+
         /// <summary>
         /// Gets all <see cref="PerspexProperty"/>s registered on a type.
         /// </summary>

Perspex/PriorityValue.cs

@@ -25,6 +25,10 @@ namespace Perspex
         private List<IObserver<Tuple<object, object>>> observers = 
             new List<IObserver<Tuple<object, object>>>();
 
+        private int defer;
+
+        private bool dirty;
+
         public object LocalValue
         {
             get
@@ -113,18 +117,41 @@ namespace Perspex
             return Disposable.Create(() => this.observers.Remove(observer));
         }
 
-        private void Push()
+        public void BeginDeferStyleChanges()
         {
-            object value = this.GetEffectiveValue();
+            if (this.defer++ == 0)
+            {
+                this.dirty = false;
+            }
+        }
 
-            if (!object.Equals(this.lastValue, value))
+        public void EndDeferStyleChanges()
+        {
+            if (this.defer > 0 && --this.defer == 0 && dirty)
             {
-                foreach (IObserver<Tuple<object, object>> observer in this.observers)
+                this.Push();
+            }        
+        }
+
+        private void Push()
+        {
+            if (defer == 0)
+            {
+                object value = this.GetEffectiveValue();
+
+                if (!object.Equals(this.lastValue, value))
                 {
-                    observer.OnNext(Tuple.Create(this.lastValue, value));
-                }
+                    foreach (IObserver<Tuple<object, object>> observer in this.observers)
+                    {
+                        observer.OnNext(Tuple.Create(this.lastValue, value));
+                    }
 
-                this.lastValue = value;
+                    this.lastValue = value;
+                }
+            }
+            else
+            {
+                dirty = true;
             }
         }
 

Perspex/Styling/IStyleable.cs

@@ -17,7 +17,7 @@ namespace Perspex.Styling
         /// <summary>
         /// Gets the list of classes for the control.
         /// </summary>
-        PerspexList<string> Classes { get; }
+        Classes Classes { get; }
 
         /// <summary>
         /// Binds a <see cref="PerspexProperty"/> to a style.