Start of work on PropertyChangedExtentsions

Stylet/ExpressionExtensions.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Stylet
+{
+    public static class ExpressionExtensions
+    {
+        public static string NameForProperty<TDelegate>(this Expression<TDelegate> propertyExpression)
+        {
+            Expression body;
+            if (propertyExpression.Body is UnaryExpression)
+                body = ((UnaryExpression)propertyExpression.Body).Operand;
+            else
+                body = propertyExpression.Body;
+
+            var member = body as MemberExpression;
+            if (member == null)
+                throw new ArgumentException("Property must be a MemberExpression");
+
+            return member.Member.Name;
+        }
+    }
+}

Stylet/PropertyChangedBase.cs

@@ -20,12 +20,7 @@ namespace Stylet
 
         protected void NotifyOfPropertyChange<TProperty>(Expression<Func<TProperty>> property)
         {
-            string propertyName;
-            if (property.Body is UnaryExpression)
-                propertyName = ((MemberExpression)((UnaryExpression)property.Body).Operand).Member.Name;
-            else
-                propertyName = ((MemberExpression)property.Body).Member.Name;
-            this.NotifyOfPropertyChange(propertyName);
+            this.NotifyOfPropertyChange(property.NameForProperty());
         }
 
         protected virtual void NotifyOfPropertyChange([CallerMemberName] string propertyName = "")

Stylet/PropertyChangedExtensions.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Runtime.CompilerServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Stylet
+{
+    public static class PropertyChangedExtensions
+    {
+        private static ConditionalWeakTable<INotifyPropertyChanged, List<Listener> eventMapping = new ConditionalWeakTable<INotifyPropertyChanged, List<Listener>();
+        private static object eventMappingLock = new object();
+
+        private class Listener
+        {
+            public readonly string PropertyName;
+            public readonly EventHandler<PropertyChangedEventArgs> Handler;
+
+            public Listener(string propertyName, EventHandler<PropertyChangedEventArgs> handler)
+            {
+                this.PropertyName = propertyName;
+                this.Handler = handler;
+            }
+        }
+
+        public static void Bind<TClass, TMember>(this TClass item, Expression<Func<TClass, TMember>> selector, Action<TMember> handler) where TClass : INotifyPropertyChanged
+        {
+            var propertyName = selector.NameForProperty();
+            var compiledSelector = selector.Compile();
+            List<Listener> listeners;
+            EventHandler<PropertyChangedEventArgs> ourHandler;
+
+            lock (eventMappingLock)
+            {
+                if (!eventMapping.TryGetValue(item, out listeners))
+                {
+                    listeners = new List<Listener>();
+                    eventMapping.Add(item, listeners);
+                }
+
+                ourHandler = (s, e) => handler(compiledSelector(item));
+
+                listeners.Add(new Listener(propertyName, ourHandler));
+            }
+
+            PropertyChangedEventManager.AddHandler(item, ourHandler, propertyName);
+        }
+    }
+}

Stylet/Stylet.csproj

@@ -56,12 +56,14 @@
     <Compile Include="EventAggregator.cs" />
     <Compile Include="EventCommand.cs" />
     <Compile Include="Execute.cs" />
+    <Compile Include="ExpressionExtensions.cs" />
     <Compile Include="IConductor.cs" />
     <Compile Include="IoC.cs" />
     <Compile Include="Bootstrapper.cs" />
     <Compile Include="IScreen.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="PropertyChangedBase.cs" />
+    <Compile Include="PropertyChangedExtensions.cs" />
     <Compile Include="Screen.cs" />
     <Compile Include="ScreenExtensions.cs" />
     <Compile Include="StyletIoC\BuilderUpper.cs" />