Added ListenIncludeLatest method to MessageBus to receive last sended…

… message.

ReactiveUI/Interfaces.cs

@@ -294,6 +294,19 @@ public interface IMessageBus : IEnableLogger
         /// <returns></returns>
         IObservable<T> Listen<T>(string contract = null);
 
+        /// <summary>
+        /// ListenIncludeLatest provides an Observable that will fire whenever a Message is
+        /// provided for this object via RegisterMessageSource or SendMessage and fire the 
+        /// last provided Message immediately if applicable, or null.
+        /// </summary>
+        /// <typeparam name="T">The type of the message to listen to.</typeparam>
+        /// <param name="contract">A unique string to distinguish messages with
+        /// identical types (i.e. "MyCoolViewModel") - if the message type is
+        /// only used for one purpose, leave this as null.</param>
+        /// <returns>An Observable representing the notifications posted to the
+        /// message bus.</returns>
+        IObservable<T> ListenIncludeLatest<T>(string contract = null);
+
         /// <summary>
         /// Determines if a particular message Type is registered.
         /// </summary>

ReactiveUI/MessageBus.cs

@@ -54,6 +54,23 @@ public IObservable<T> Listen<T>(string contract = null)
         {
             this.Log().Info("Listening to {0}:{1}", typeof (T), contract);
 
+            return SetupSubjectIfNecessary<T>(contract).Skip(1);
+        }
+
+        /// <summary>
+        /// Listen provides an Observable that will fire whenever a Message is
+        /// provided for this object via RegisterMessageSource or SendMessage.
+        /// </summary>
+        /// <typeparam name="T">The type of the message to listen to.</typeparam>
+        /// <param name="contract">A unique string to distinguish messages with
+        /// identical types (i.e. "MyCoolViewModel") - if the message type is
+        /// only used for one purpose, leave this as null.</param>
+        /// <returns>An Observable representing the notifications posted to the
+        /// message bus.</returns>
+        public IObservable<T> ListenIncludeLatest<T>(string contract = null)
+        {
+            this.Log().Info("Listening to {0}:{1}", typeof(T), contract);
+
             return SetupSubjectIfNecessary<T>(contract);
         }
 
@@ -126,7 +143,7 @@ ISubject<T> SetupSubjectIfNecessary<T>(string contract)
                     return;
                 }
 
-                ret = new ScheduledSubject<T>(GetScheduler(tuple));
+                ret = new ScheduledSubject<T>(GetScheduler(tuple), null, new BehaviorSubject<T>(default(T)));
                 mb[tuple] = new NotAWeakReference(ret);
             });