Tidied up PseudoClass stuff.

Make it more like AffectsMeasure etc. To do this required a
PerspexProperty.Initialized observable.

Perspex.Base/PerspexObject.cs

@@ -77,6 +77,23 @@ namespace Perspex
         private Dictionary<PerspexProperty, PriorityValue> values =
             new Dictionary<PerspexProperty, PriorityValue>();
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PerspexObject"/> class.
+        /// </summary>
+        public PerspexObject()
+        {
+            foreach (var p in this.GetAllValues())
+            {
+                var e = new PerspexPropertyChangedEventArgs(
+                    this, 
+                    p.Property, 
+                    PerspexProperty.UnsetValue, 
+                    p.CurrentValue);
+
+                p.Property.NotifyInitialized(e);
+            }
+        }
+
         /// <summary>
         /// Event handler for <see cref="INotifyPropertyChanged"/> implementation.
         /// </summary>

Perspex.Base/PerspexProperty.cs

@@ -29,6 +29,11 @@ namespace Perspex
         /// </summary>
         private Dictionary<Type, object> defaultValues = new Dictionary<Type, object>();
 
+        /// <summary>
+        /// Observable fired when this property changes on any <see cref="PerspexObject"/>.
+        /// </summary>
+        private Subject<PerspexPropertyChangedEventArgs> initialized = new Subject<PerspexPropertyChangedEventArgs>();
+
         /// <summary>
         /// Observable fired when this property changes on any <see cref="PerspexObject"/>.
         /// </summary>
@@ -89,6 +94,21 @@ namespace Perspex
         /// <returns></returns>
         public BindingMode DefaultBindingMode { get; private set; }
 
+        /// <summary>
+        /// Gets an observable that is fired when this property is initialized on a
+        /// new <see cref="PerspexObject"/> instance.
+        /// </summary>
+        /// <remarks>
+        /// This observable is fired each time a new <see cref="PerspexObject"/> is constructed
+        /// for all properties registered on the object's type. The default value of the property 
+        /// for the object is passed in the args' NewValue (OldValue will always be 
+        /// <see cref="UnsetValue"/>.
+        /// </remarks>
+        public IObservable<PerspexPropertyChangedEventArgs> Initialized
+        {
+            get { return this.initialized; }
+        }
+
         /// <summary>
         /// Gets an observable that is fired when this property changes on any 
         /// <see cref="PerspexObject"/> instance.
@@ -270,6 +290,11 @@ namespace Perspex
             return this.Name;
         }
 
+        internal void NotifyInitialized(PerspexPropertyChangedEventArgs e)
+        {
+            this.initialized.OnNext(e);
+        }
+
         internal void NotifyChanged(PerspexPropertyChangedEventArgs e)
         {
             this.changed.OnNext(e);

Perspex.Controls/Control.cs

@@ -33,7 +33,7 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<ITemplatedControl> TemplatedParentProperty =
             PerspexProperty.Register<Control, ITemplatedControl>("TemplatedParent", inherits: true);
 
-        private Classes classes;
+        private Classes classes = new Classes();
 
         private DataTemplates dataTemplates;
 
@@ -44,13 +44,8 @@ namespace Perspex.Controls
         static Control()
         {
             AffectsMeasure(IsVisibleProperty);
-        }
-
-        public Control()
-        {
-            this.classes = new Classes();
-            this.AddPseudoClass(IsPointerOverProperty, ":pointerover");
-            this.AddPseudoClass(IsFocusedProperty, ":focus");
+            PseudoClass(IsPointerOverProperty, ":pointerover");
+            PseudoClass(IsFocusedProperty, ":focus");
         }
 
         public Brush Background
@@ -159,25 +154,44 @@ namespace Perspex.Controls
             internal set { this.SetValue(TemplatedParentProperty, value); }
         }
 
-        protected override void OnAttachedToVisualTree(IRenderRoot root)
+        protected static void PseudoClass(PerspexProperty<bool> property, string className)
         {
-            IStyler styler = Locator.Current.GetService<IStyler>();
-            styler.ApplyStyles(this);
+            PseudoClass(property, x => x, className);
         }
 
-        protected void AddPseudoClass(PerspexProperty<bool> property, string className)
+        protected static void PseudoClass<T>(
+            PerspexProperty<T> property, 
+            Func<T, bool> selector, 
+            string className)
         {
-            this.GetObservable(property).Subscribe(x =>
+            Contract.Requires<ArgumentNullException>(property != null);
+            Contract.Requires<ArgumentNullException>(selector != null);
+            Contract.Requires<ArgumentNullException>(className != null);
+            Contract.Requires<ArgumentNullException>(property != null);
+
+            if (string.IsNullOrWhiteSpace(className))
             {
-                if (x)
-                {
-                    this.classes.Add(className);
-                }
-                else
+                throw new ArgumentException("Cannot supply an empty className.");
+            }
+
+            Observable.Merge(property.Changed, property.Initialized)
+                .Subscribe(e =>
                 {
-                    this.classes.Remove(className);
-                }
-            });
+                    if (selector((T)e.NewValue))
+                    {
+                        ((Control)e.Sender).Classes.Add(className);
+                    }
+                    else
+                    {
+                        ((Control)e.Sender).Classes.Remove(className);
+                    }
+                });
+        }
+
+        protected override void OnAttachedToVisualTree(IRenderRoot root)
+        {
+            IStyler styler = Locator.Current.GetService<IStyler>();
+            styler.ApplyStyles(this);
         }
     }
 }

Perspex.Controls/Primitives/ScrollBar.cs

@@ -26,21 +26,10 @@ namespace Perspex.Controls.Primitives
         public static readonly PerspexProperty<Orientation> OrientationProperty =
             PerspexProperty.Register<ScrollBar, Orientation>("Orientation");
 
-        public ScrollBar()
+        static ScrollBar()
         {
-            this.GetObservable(OrientationProperty).Subscribe(o =>
-            {
-                if (o == Orientation.Horizontal)
-                {
-                    this.Classes.Remove(":vertical");
-                    this.Classes.Add(":horizontal");
-                }
-                else
-                {
-                    this.Classes.Remove(":horizontal");
-                    this.Classes.Add(":vertical");
-                }
-            });
+            PseudoClass(OrientationProperty, x => x == Orientation.Horizontal, ":horizontal");
+            PseudoClass(OrientationProperty, x => x == Orientation.Vertical, ":vertical");
         }
 
         public double Minimum

Perspex.Controls/Primitives/ToggleButton.cs

@@ -13,10 +13,14 @@ namespace Perspex.Controls.Primitives
         public static readonly PerspexProperty<bool> IsCheckedProperty =
             PerspexProperty.Register<ToggleButton, bool>("IsChecked");
 
+        static ToggleButton()
+        {
+            PseudoClass(IsCheckedProperty, ":checked");
+        }
+
         public ToggleButton()
         {
             this.Click += (s, e) => this.IsChecked = !this.IsChecked;
-            this.AddPseudoClass(IsCheckedProperty, ":checked");
         }
 
         public bool IsChecked

Perspex.Controls/TabItem.cs

@@ -13,10 +13,10 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<bool> IsSelectedProperty =
             PerspexProperty.Register<TabItem, bool>("IsSelected");
 
-        public TabItem()
+        static TabItem()
         {
-            this.AddPseudoClass(IsSelectedProperty, ":selected");
             AffectsRender(IsSelectedProperty);
+            PseudoClass(IsSelectedProperty, ":selected");
         }
 
         public bool IsSelected

Perspex.Controls/TreeViewItem.cs

@@ -21,9 +21,13 @@ namespace Perspex.Controls
 
         TreeView treeView;
 
+        static TreeViewItem()
+        {
+            PseudoClass(IsSelectedProperty, ":selected");
+        }
+
         public TreeViewItem()
         {
-            this.AddPseudoClass(IsSelectedProperty, ":selected");
             AffectsRender(IsSelectedProperty);
         }
 

Perspex.UnitTests/PerspexPropertyTests.cs

@@ -83,22 +83,33 @@ namespace Perspex.UnitTests
             Assert.AreEqual("Bar", target.GetDefaultValue<Class2>());
         }
 
+        [TestMethod]
+        public void Initialized_Observable_Fired()
+        {
+            string value = null;
+
+            Class1.FooProperty.Initialized.Subscribe(x => value = (string)x.NewValue);
+            var target = new Class1();
+
+            Assert.AreEqual("default", value);
+        }
+
         [TestMethod]
         public void Changed_Observable_Fired()
         {
             var target = new Class1();
-            bool fired = false;
+            string value = null;
 
-            Class1.FooProperty.Changed.Subscribe(x => fired = true);
+            Class1.FooProperty.Changed.Subscribe(x => value = (string)x.NewValue);
             target.SetValue(Class1.FooProperty, "newvalue");
 
-            Assert.IsTrue(fired);
+            Assert.AreEqual("newvalue", value);
         }
 
         private class Class1 : PerspexObject
         {
             public static readonly PerspexProperty<string> FooProperty = 
-                PerspexProperty.Register<Class1, string>("Foo");
+                PerspexProperty.Register<Class1, string>("Foo", "default");
         }
 
         private class Class2 : Class1

Perspex.sln

@@ -76,7 +76,6 @@ Global
 		{DABFD304-D6A4-4752-8123-C2CCF7AC7831}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{DABFD304-D6A4-4752-8123-C2CCF7AC7831}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{DABFD304-D6A4-4752-8123-C2CCF7AC7831}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{DABFD304-D6A4-4752-8123-C2CCF7AC7831}.Release|Any CPU.Build.0 = Release|Any CPU
 		{B09B78D8-9B26-48B0-9149-D64A2F120F3F}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{B09B78D8-9B26-48B0-9149-D64A2F120F3F}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{B09B78D8-9B26-48B0-9149-D64A2F120F3F}.Release|Any CPU.ActiveCfg = Release|Any CPU