Added PerspexObservable.

Similar to Rx's AnonymousObservable that is created using
Observable.Create, but it also implements IDescription. This description
is populated when created by PerspexObject.GetObservable.

Perspex.Base/PerspexObject.cs

@@ -15,7 +15,7 @@ namespace Perspex
     using Perspex.Diagnostics;
     using Splat;
     using System.Reactive.Disposables;
-
+    using Perspex.Reactive;
 
     /// <summary>
     /// The priority of a binding.
@@ -306,7 +306,7 @@ namespace Perspex
         {
             Contract.Requires<NullReferenceException>(property != null);
 
-            return Observable.Create<object>(observer =>
+            return new PerspexObservable<object>(observer =>
             {
                 EventHandler<PerspexPropertyChangedEventArgs> handler = (s, e) =>
                 {
@@ -318,19 +318,19 @@ namespace Perspex
 
                 this.PropertyChanged += handler;
 
-                return () =>
+                return Disposable.Create(() =>
                 {
                     this.PropertyChanged -= handler;
-                };
+                });
-            }).StartWith(this.GetValue(property));
+            }, this.GetObservableDescription(property)).StartWith(this.GetValue(property));
         }
 
         /// <summary>
         /// Gets an observable for a <see cref="PerspexProperty"/>.
         /// </summary>
-        /// <typeparam name="T"></typeparam>
+        /// <typeparam name="T">The property type.</typeparam>
-        /// <param name="property"></param>
+        /// <param name="property">The property.</param>
-        /// <returns></returns>
+        /// <returns>An observable.</returns>
         public IObservable<T> GetObservable<T>(PerspexProperty<T> property)
         {
             Contract.Requires<NullReferenceException>(property != null);
@@ -346,7 +346,7 @@ namespace Perspex
         /// <returns></returns>
         public IObservable<Tuple<T, T>> GetObservableWithHistory<T>(PerspexProperty<T> property)
         {
-            return Observable.Create<Tuple<T, T>>(observer =>
+            return new PerspexObservable<Tuple<T, T>>(observer =>
             {
                 EventHandler<PerspexPropertyChangedEventArgs> handler = (s, e) =>
                 {
@@ -358,11 +358,11 @@ namespace Perspex
 
                 this.PropertyChanged += handler;
 
-                return () =>
+                return Disposable.Create(() =>
                 {
                     this.PropertyChanged -= handler;
-                };
+                });
-            });
+            }, this.GetObservableDescription(property));
         }
 
         /// <summary>
@@ -759,6 +759,16 @@ namespace Perspex
             }
         }
 
+        /// <summary>
+        /// Gets a description of a property that van be used in observables.
+        /// </summary>
+        /// <param name="property">The property</param>
+        /// <returns>The description.</returns>
+        private string GetObservableDescription(PerspexProperty property)
+        {
+            return string.Format("{0}.{1}", this.GetType().Name, property.Name);
+        }
+
         /// <summary>
         /// Raises the <see cref="PropertyChanged"/> event.
         /// </summary>

Perspex.Base/Reactive/PerspexObservable.cs

@@ -0,0 +1,35 @@
+// -----------------------------------------------------------------------
+// <copyright file="PerspexObject.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Reactive
+{
+    using System;
+    using System.Reactive;
+    using System.Reactive.Disposables;
+
+    public sealed class PerspexObservable<T> : ObservableBase<T>, IDescription
+    {
+        private readonly Func<IObserver<T>, IDisposable> subscribe;
+
+        public string Description { get; }
+
+        public PerspexObservable(Func<IObserver<T>, IDisposable> subscribe, string description)
+        {
+            if (subscribe == null)
+            {
+                throw new ArgumentNullException("subscribe");
+            }
+
+            this.subscribe = subscribe;
+            this.Description = description;
+        }
+
+        protected override IDisposable SubscribeCore(IObserver<T> observer)
+        {
+            return this.subscribe(observer) ?? Disposable.Empty;
+        }
+    }
+}