Merge branch 'binding-refactor'

samples/TestApplicationShared/App.cs

@@ -21,11 +21,8 @@ namespace TestApplication
             {
                 new FuncTreeDataTemplate<Node>(
                     x => new TextBlock {Text = x.Name},
-                    x => x.Children,
+                    x => x.Children),
-                    x => true),
             };
         }
-
-
     }
 }

samples/TestApplicationShared/GalleryStyle.cs

@@ -23,7 +23,7 @@ namespace TestApplication
                 {
                     Setters = new[]
                     {
-                        new Setter (TemplatedControl.TemplateProperty, new FuncControlTemplate<TabControl> (TabControlTemplate))
+                        new Setter (TemplatedControl.TemplateProperty, new FuncControlTemplate<TabControl>(TabControlTemplate))
                     }
                 },
 

samples/TestApplicationShared/MainWindow.cs

@@ -11,6 +11,7 @@ using Perspex.Controls.Html;
 using Perspex.Controls.Primitives;
 using Perspex.Controls.Shapes;
 using Perspex.Controls.Templates;
+using Perspex.Data;
 using Perspex.Diagnostics;
 using Perspex.Layout;
 using Perspex.Media;

samples/XamlTestApplicationPcl/ViewModels/MainWindowViewModel.cs

@@ -1,7 +1,9 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System;
 using System.Collections.Generic;
+using ReactiveUI;
 
 namespace XamlTestApplication.ViewModels
 {
@@ -22,6 +24,7 @@ namespace XamlTestApplication.ViewModels
                 {
                     Header = "Root",
                     SubHeader = "Root Item",
+                    IsExpanded = true,
                     Children = new[]
                     {
                         new TestNode
@@ -33,6 +36,7 @@ namespace XamlTestApplication.ViewModels
                         {
                             Header = "Child 2",
                             SubHeader = "Child 2 Value",
+                            IsExpanded = false,
                             Children = new[]
                             {
                                 new TestNode
@@ -50,9 +54,39 @@ namespace XamlTestApplication.ViewModels
                     }
                 }
             };
+
+            CollapseNodesCommand = ReactiveCommand.Create();
+            CollapseNodesCommand.Subscribe(_ => ExpandNodes(false));
+            ExpandNodesCommand = ReactiveCommand.Create();
+            ExpandNodesCommand.Subscribe(_ => ExpandNodes(true));
         }
 
         public List<TestItem> Items { get; }
         public List<TestNode> Nodes { get; }
+
+        public ReactiveCommand<object> CollapseNodesCommand { get; }
+
+        public ReactiveCommand<object> ExpandNodesCommand { get; }
+
+        public void ExpandNodes(bool expanded)
+        {
+            foreach (var node in Nodes)
+            {
+                ExpandNodes(node, expanded);
+            }
+        }
+
+        private void ExpandNodes(TestNode node, bool expanded)
+        {
+            node.IsExpanded = expanded;
+
+            if (node.Children != null)
+            {
+                foreach (var child in node.Children)
+                {
+                    ExpandNodes(child, expanded);
+                }
+            }
+        }
     }
 }

samples/XamlTestApplicationPcl/ViewModels/TestNode.cs

@@ -2,13 +2,22 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System.Collections.Generic;
+using ReactiveUI;
 
 namespace XamlTestApplication.ViewModels
 {
-    public class TestNode
+    public class TestNode : ReactiveObject
     {
+        private bool _isExpanded;
+
         public string Header { get; set; }
         public string SubHeader { get; set; }
         public IEnumerable<TestNode> Children { get; set; }
+
+        public bool IsExpanded
+        {
+            get { return _isExpanded; }
+            set { this.RaiseAndSetIfChanged(ref this._isExpanded, value); }
+        }
     }
 }

samples/XamlTestApplicationPcl/Views/MainWindow.paml

@@ -147,6 +147,11 @@
                       </StackPanel>
                   </DropDown>
                   <TreeView Items="{Binding Nodes}">
+                      <TreeView.Styles>
+                          <Style Selector="TreeViewItem">
+                              <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}"/>
+                          </Style>
+                      </TreeView.Styles>
                       <TreeView.DataTemplates>
                           <TreeDataTemplate DataType="vm:TestNode" ItemsSource="{Binding Children}">
                               <StackPanel>
@@ -156,6 +161,10 @@
                           </TreeDataTemplate>
                       </TreeView.DataTemplates>
                   </TreeView>
+                  <StackPanel Orientation="Vertical" Gap="4">
+                      <Button Command="{Binding CollapseNodesCommand}">Collapse Nodes</Button>
+                      <Button Command="{Binding ExpandNodesCommand}">Expand Nodes</Button>
+                  </StackPanel>
               </StackPanel>
           </TabItem>
           <TabItem Header="Layout">

samples/XamlTestApplicationPcl/XamlTestApplicationPcl.csproj

@@ -123,6 +123,22 @@
       <HintPath>..\..\packages\Splat.1.6.2\lib\Portable-net45+win+wpa81+wp80\Splat.dll</HintPath>
       <Private>True</Private>
     </Reference>
+    <Reference Include="System.Reactive.Core, Version=2.2.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Rx-Core.2.2.5\lib\portable-windows8+net45+wp8\System.Reactive.Core.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="System.Reactive.Interfaces, Version=2.2.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Rx-Interfaces.2.2.5\lib\portable-windows8+net45+wp8\System.Reactive.Interfaces.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="System.Reactive.Linq, Version=2.2.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Rx-Linq.2.2.5\lib\portable-windows8+net45+wp8\System.Reactive.Linq.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="System.Reactive.PlatformServices, Version=2.2.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Rx-PlatformServices.2.2.5\lib\portable-windows8+net45+wp8\System.Reactive.PlatformServices.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="XamlTestApp.paml">

samples/XamlTestApplicationPcl/packages.config

@@ -1,4 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="Rx-Core" version="2.2.5" targetFramework="portable45-net45+win8" />
+  <package id="Rx-Interfaces" version="2.2.5" targetFramework="portable45-net45+win8" />
+  <package id="Rx-Linq" version="2.2.5" targetFramework="portable45-net45+win8" />
+  <package id="Rx-Main" version="2.2.5" targetFramework="portable45-net45+win8" />
+  <package id="Rx-PlatformServices" version="2.2.5" targetFramework="portable45-net45+win8" />
   <package id="Splat" version="1.6.2" targetFramework="portable45-net45+win8" />
 </packages>

src/Markup/Perspex.Markup.Xaml/Context/PerspexWiringContext.cs

@@ -15,6 +15,7 @@ using Perspex.Controls.Primitives;
 using Perspex.Controls.Templates;
 using Perspex.Input;
 using Perspex.Markup.Xaml.Converters;
+using Perspex.Markup.Xaml.Data;
 using Perspex.Media;
 using Perspex.Media.Imaging;
 using Perspex.Metadata;
@@ -58,9 +59,10 @@ namespace Perspex.Markup.Xaml.Context
 
             var forcedAssemblies = new[]
             {
+                typeof(Binding),
                 typeof(Control),
-                typeof(Style),
                 typeof(IValueConverter),
+                typeof(Style),
             }.Select(t => t.GetTypeInfo().Assembly);
 
             foreach (var nsa in 

src/Markup/Perspex.Markup.Xaml/Context/PerspexXamlMemberValuePlugin.cs

@@ -9,6 +9,8 @@ using System.Runtime.CompilerServices;
 using Glass;
 using OmniXaml.ObjectAssembler;
 using OmniXaml.Typing;
+using Perspex.Controls;
+using Perspex.Data;
 using Perspex.Markup.Xaml.Data;
 using Perspex.Styling;
 
@@ -39,9 +41,9 @@ namespace Perspex.Markup.Xaml.Context
 
         public override void SetValue(object instance, object value)
         {
-            if (value is IXamlBinding)
+            if (value is IBinding)
             {
-                HandleBinding(instance, (IXamlBinding)value);
+                HandleBinding(instance, (IBinding)value);
             }
             else if (IsPerspexProperty)
             {
@@ -68,35 +70,38 @@ namespace Perspex.Markup.Xaml.Context
             po.SetValue(pp, value);
         }
 
-        private void HandleBinding(object instance, IXamlBinding binding)
+        private void HandleBinding(object instance, IBinding binding)
         {
-            if (typeof(IXamlBinding).GetTypeInfo().IsAssignableFrom(_xamlMember.XamlType.UnderlyingType.GetTypeInfo()))
+            if (!(AssignBinding(instance, binding) || ApplyBinding(instance, binding)))
             {
-                var property = instance.GetType().GetRuntimeProperty(_xamlMember.Name);
+                throw new InvalidOperationException(
+                    $"Cannot assign to '{_xamlMember.Name}' on '{instance.GetType()}");
+            }
+        }
 
-                if (property == null || !property.CanWrite)
+        private bool AssignBinding(object instance, IBinding binding)
-                {
+        {
-                    throw new InvalidOperationException(
+            var property = instance.GetType()
-                        $"Cannot assign to '{_xamlMember.Name}' on '{instance.GetType()}");
+                .GetRuntimeProperties()
-                }
+                .FirstOrDefault(x => x.Name == _xamlMember.Name);
 
+            if (property?.GetCustomAttribute<AssignBindingAttribute>() != null)
+            {
                 property.SetValue(instance, binding);
+                return true;
             }
-            else
+
-            {
+            return false;
-                ApplyBinding(instance, binding);
-            }                
         }
 
-        private void ApplyBinding(object instance, IXamlBinding binding)
+        private bool ApplyBinding(object instance, IBinding binding)
         {
-            var perspexObject = instance as PerspexObject;
+            var targetControl = instance as IControl;
             var attached = _xamlMember as PerspexAttachableXamlMember;
 
-            if (perspexObject == null)
+            if (targetControl == null)
             {
-                throw new InvalidOperationException(
+                return false;
-                    $"Cannot bind to an object of type '{instance.GetType()}");
             }
 
             PerspexProperty property;
@@ -105,7 +110,7 @@ namespace Perspex.Markup.Xaml.Context
             if (attached == null)
             {
                 propertyName = _xamlMember.Name;
-                property = PerspexPropertyRegistry.Instance.GetRegistered(perspexObject)
+                property = PerspexPropertyRegistry.Instance.GetRegistered((PerspexObject)targetControl)
                     .FirstOrDefault(x => x.Name == propertyName);
             }
             else
@@ -115,18 +120,18 @@ namespace Perspex.Markup.Xaml.Context
 
                 propertyName = attached.DeclaringType.UnderlyingType.Name + '.' + _xamlMember.Name;
 
-                property = PerspexPropertyRegistry.Instance.GetRegistered(perspexObject)
+                property = PerspexPropertyRegistry.Instance.GetRegistered((PerspexObject)targetControl)
                     .Where(x => x.IsAttached && x.OwnerType == attached.DeclaringType.UnderlyingType)
                     .FirstOrDefault(x => x.Name == _xamlMember.Name);
             }
 
             if (property == null)
             {
-                throw new InvalidOperationException(
+                return false;
-                    $"Cannot find '{propertyName}' on '{instance.GetType()}");
             }
 
-            binding.Bind(perspexObject, property);
+            targetControl.Bind(property, binding);
+            return true;
         }
 
         private bool ValueRequiresSpecialHandling(object value)

src/Markup/Perspex.Markup.Xaml/Data/Binding.cs

@@ -6,6 +6,7 @@ using System.Reactive;
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
 using Perspex.Controls;
+using Perspex.Data;
 using Perspex.Markup.Data;
 
 namespace Perspex.Markup.Xaml.Data
@@ -13,7 +14,7 @@ namespace Perspex.Markup.Xaml.Data
     /// <summary>
     /// A XAML binding.
     /// </summary>
-    public class Binding : IXamlBinding
+    public class Binding : IBinding
     {
         /// <summary>
         /// Gets or sets the <see cref="IValueConverter"/> to use.
@@ -50,66 +51,41 @@ namespace Perspex.Markup.Xaml.Data
         /// </summary>
         public string Path { get; set; }
 
-        /// <summary>
-        /// Applies the binding to a property on an instance.
-        /// </summary>
-        /// <param name="instance">The target instance.</param>
-        /// <param name="property">The target property.</param>
-        public void Bind(IObservablePropertyBag instance, PerspexProperty property)
-        {
-            Contract.Requires<ArgumentNullException>(instance != null);
-            Contract.Requires<ArgumentNullException>(property != null);
-
-            var subject = CreateSubject(
-                instance,
-                property.PropertyType,
-                property == Control.DataContextProperty);
-
-            if (subject != null)
-            {
-                Bind(instance, property, subject);
-            }
-        }
-
         /// <summary>
         /// Creates a subject that can be used to get and set the value of the binding.
         /// </summary>
         /// <param name="target">The target instance.</param>
-        /// <param name="targetType">The type of the target property.</param>
+        /// <param name="targetProperty">The target property. May be null.</param>
-        /// <param name="targetIsDataContext">
+        /// <returns>An <see cref="ISubject{Object}"/>.</returns>
-        /// Whether the target property is the DataContext property.
-        /// </param>
-        /// <returns>An <see cref="ISubject{object}"/>.</returns>
         public ISubject<object> CreateSubject(
-            IObservablePropertyBag target,
+            IPerspexObject target, 
-            Type targetType,
+            PerspexProperty targetProperty)
-            bool targetIsDataContext = false)
         {
             Contract.Requires<ArgumentNullException>(target != null);
-            Contract.Requires<ArgumentNullException>(targetType != null);
 
             var pathInfo = ParsePath(Path);
             ValidateState(pathInfo);
 
             ExpressionObserver observer;
+            var targetIsDataContext = targetProperty == Control.DataContextProperty;
 
             if (pathInfo.ElementName != null || ElementName != null)
             {
-                observer = CreateElementSubject(
+                observer = CreateElementObserver(
                     (IControl)target, 
                     pathInfo.ElementName ?? ElementName, 
                     pathInfo.Path);
             }
             else if (RelativeSource == null || RelativeSource.Mode == RelativeSourceMode.DataContext)
             {
-                observer = CreateDataContextSubject(
+                observer = CreateDataContexObserver(
                     target, 
                     pathInfo.Path,
                     targetIsDataContext);
             }
             else if (RelativeSource.Mode == RelativeSourceMode.TemplatedParent)
             {
-                observer = CreateTemplatedParentSubject(
+                observer = CreateTemplatedParentObserver(
                     target,
                     pathInfo.Path);
             }
@@ -120,47 +96,11 @@ namespace Perspex.Markup.Xaml.Data
 
             return new ExpressionSubject(
                 observer,
-                targetType,
+                targetProperty?.PropertyType ?? typeof(object),
                 Converter ?? DefaultValueConverter.Instance,
                 ConverterParameter);
         }
 
-        /// <summary>
-        /// Applies a binding subject to a property on an instance.
-        /// </summary>
-        /// <param name="target">The target instance.</param>
-        /// <param name="property">The target property.</param>
-        /// <param name="subject">The binding subject.</param>
-        internal void Bind(IObservablePropertyBag target, PerspexProperty property, ISubject<object> subject)
-        {
-            Contract.Requires<ArgumentNullException>(target != null);
-            Contract.Requires<ArgumentNullException>(property != null);
-            Contract.Requires<ArgumentNullException>(subject != null);
-
-            var mode = Mode == BindingMode.Default ?
-                property.DefaultBindingMode : Mode;
-
-            switch (mode)
-            {
-                case BindingMode.Default:
-                case BindingMode.OneWay:
-                    target.Bind(property, subject, Priority);
-                    break;
-                case BindingMode.TwoWay:
-                    target.BindTwoWay(property, subject, Priority);
-                    break;
-                case BindingMode.OneTime:
-                    target.GetObservable(Control.DataContextProperty).Subscribe(dataContext =>
-                    {
-                        subject.Take(1).Subscribe(x => target.SetValue(property, x, Priority));
-                    });
-                    break;
-                case BindingMode.OneWayToSource:
-                    target.GetObservable(property).Subscribe(subject);
-                    break;
-            }
-        }
-
         private static PathInfo ParsePath(string path)
         {
             var result = new PathInfo();
@@ -208,8 +148,8 @@ namespace Perspex.Markup.Xaml.Data
             }
         }
 
-        private ExpressionObserver CreateDataContextSubject(
+        private ExpressionObserver CreateDataContexObserver(
-            IObservablePropertyBag target,
+            IPerspexObject target,
             string path,
             bool targetIsDataContext)
         {
@@ -231,15 +171,15 @@ namespace Perspex.Markup.Xaml.Data
             {
                 return new ExpressionObserver(
                     target.GetObservable(Visual.VisualParentProperty)
-                          .OfType<IObservablePropertyBag>()
+                          .OfType<IPerspexObject>()
                           .Select(x => x.GetObservable(Control.DataContextProperty))
                           .Switch(),
                     path);
             }
         }
 
-        private ExpressionObserver CreateTemplatedParentSubject(
+        private ExpressionObserver CreateTemplatedParentObserver(
-            IObservablePropertyBag target,
+            IPerspexObject target,
             string path)
         {
             Contract.Requires<ArgumentNullException>(target != null);
@@ -256,7 +196,7 @@ namespace Perspex.Markup.Xaml.Data
             return result;
         }
 
-        private ExpressionObserver CreateElementSubject(
+        private ExpressionObserver CreateElementObserver(
             IControl target,
             string elementName,
             string path)

src/Markup/Perspex.Markup.Xaml/Data/IXamlBinding.cs

@@ -1,35 +0,0 @@
-// Copyright (c) The Perspex Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System;
-using System.Reactive.Subjects;
-
-namespace Perspex.Markup.Xaml.Data
-{
-    /// <summary>
-    /// Defines a binding that can be created in XAML markup.
-    /// </summary>
-    public interface IXamlBinding
-    {
-        /// <summary>
-        /// Applies the binding to a property on an instance.
-        /// </summary>
-        /// <param name="instance">The target instance.</param>
-        /// <param name="property">The target property.</param>
-        void Bind(IObservablePropertyBag instance, PerspexProperty property);
-
-        /// <summary>
-        /// Creates a subject that can be used to get and set the value of the binding.
-        /// </summary>
-        /// <param name="target">The target instance.</param>
-        /// <param name="targetType">The type of the target property.</param>
-        /// <param name="targetIsDataContext">
-        /// Whether the target property is the DataContext property.
-        /// </param>
-        /// <returns>An <see cref="ISubject{object}"/>.</returns>
-        ISubject<object> CreateSubject(
-            IObservablePropertyBag target,
-            Type targetType,
-            bool targetIsDataContext = false);
-    }
-}

src/Markup/Perspex.Markup.Xaml/Data/MultiBinding.cs

@@ -8,6 +8,7 @@ using System.Linq;
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
 using Perspex.Controls;
+using Perspex.Data;
 using Perspex.Metadata;
 
 namespace Perspex.Markup.Xaml.Data
@@ -15,13 +16,13 @@ namespace Perspex.Markup.Xaml.Data
     /// <summary>
     /// A XAML binding that calculates an aggregate value from multiple child <see cref="Bindings"/>.
     /// </summary>
-    public class MultiBinding : IXamlBinding
+    public class MultiBinding : IBinding
     {
         /// <summary>
         /// Gets the collection of child bindings.
         /// </summary>
         [Content]
-        public IList<IXamlBinding> Bindings { get; set; } = new List<IXamlBinding>();
+        public IList<IBinding> Bindings { get; set; } = new List<IBinding>();
 
         /// <summary>
         /// Gets or sets the <see cref="IValueConverter"/> to use.
@@ -48,9 +49,9 @@ namespace Perspex.Markup.Xaml.Data
         /// </summary>
         /// <param name="instance">The target instance.</param>
         /// <param name="property">The target property.</param>
-        public void Bind(IObservablePropertyBag instance, PerspexProperty property)
+        public void Bind(IPerspexObject instance, PerspexProperty property)
         {
-            var subject = CreateSubject(instance, property.PropertyType);
+            var subject = CreateSubject(instance, property);
 
             if (subject != null)
             {
@@ -62,23 +63,18 @@ namespace Perspex.Markup.Xaml.Data
         /// Creates a subject that can be used to get and set the value of the binding.
         /// </summary>
         /// <param name="target">The target instance.</param>
-        /// <param name="targetType">The type of the target property.</param>
+        /// <param name="targetProperty">The target property.</param>
-        /// <param name="targetIsDataContext">
+        /// <returns>An <see cref="ISubject{Object}"/>.</returns>
-        /// Whether the target property is the DataContext property.
+        public ISubject<object> CreateSubject(IPerspexObject target, PerspexProperty targetProperty)
-        /// </param>
-        /// <returns>An <see cref="ISubject{object}"/>.</returns>
-        public ISubject<object> CreateSubject(
-            IObservablePropertyBag target, 
-            Type targetType,
-            bool targetIsDataContext = false)
         {
             if (Converter == null)
             {
                 throw new NotSupportedException("MultiBinding without Converter not currently supported.");
             }
 
+            var targetType = targetProperty?.PropertyType ?? typeof(object);
             var result = new BehaviorSubject<object>(PerspexProperty.UnsetValue);
-            var children = Bindings.Select(x => x.CreateSubject(target, typeof(object)));
+            var children = Bindings.Select(x => x.CreateSubject(target, null));
             var input = children.CombineLatest().Select(x =>
                 Converter.Convert(x, targetType, null, CultureInfo.CurrentUICulture));
             input.Subscribe(result);
@@ -91,7 +87,7 @@ namespace Perspex.Markup.Xaml.Data
         /// <param name="target">The target instance.</param>
         /// <param name="property">The target property.</param>
         /// <param name="subject">The binding subject.</param>
-        internal void Bind(IObservablePropertyBag target, PerspexProperty property, ISubject<object> subject)
+        internal void Bind(IPerspexObject target, PerspexProperty property, ISubject<object> subject)
         {
             var mode = Mode == BindingMode.Default ?
                 property.DefaultBindingMode : Mode;

src/Markup/Perspex.Markup.Xaml/MarkupExtensions/BindingExtension.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using OmniXaml;
+using Perspex.Data;
 using Perspex.Markup.Xaml.Data;
 
 namespace Perspex.Markup.Xaml.MarkupExtensions
@@ -26,6 +27,7 @@ namespace Perspex.Markup.Xaml.MarkupExtensions
                 ElementName = ElementName,
                 Mode = Mode,
                 Path = Path,
+                Priority = Priority,
             };
         }
 
@@ -34,5 +36,6 @@ namespace Perspex.Markup.Xaml.MarkupExtensions
         public string ElementName { get; set; }
         public BindingMode Mode { get; set; }
         public string Path { get; set; }
+        public BindingPriority Priority { get; set; } = BindingPriority.LocalValue;
     }
 }

src/Markup/Perspex.Markup.Xaml/MarkupExtensions/TemplateBindingExtension.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using OmniXaml;
+using Perspex.Data;
 using Perspex.Markup.Xaml.Data;
 
 namespace Perspex.Markup.Xaml.MarkupExtensions
@@ -24,9 +25,9 @@ namespace Perspex.Markup.Xaml.MarkupExtensions
                 Converter = Converter,
                 ElementName = ElementName,
                 Mode = Mode,
-                Priority = BindingPriority.TemplatedParent,
                 RelativeSource = new RelativeSource(RelativeSourceMode.TemplatedParent),
                 Path = Path,
+                Priority = Priority,
             };
         }
 
@@ -34,5 +35,6 @@ namespace Perspex.Markup.Xaml.MarkupExtensions
         public string ElementName { get; set; }
         public BindingMode Mode { get; set; }
         public string Path { get; set; }
+        public BindingPriority Priority { get; set; } = BindingPriority.TemplatedParent;
     }
 }

src/Markup/Perspex.Markup.Xaml/Perspex.Markup.Xaml.csproj

@@ -42,7 +42,6 @@
     <Compile Include="Converters\CursorTypeConverter.cs" />
     <Compile Include="Converters\PerspexListTypeConverter.cs" />
     <Compile Include="Converters\RelativeRectTypeConverter.cs" />
-    <Compile Include="Data\IXamlBinding.cs" />
     <Compile Include="Data\MultiBinding.cs" />
     <Compile Include="Data\RelativeSource.cs" />
     <Compile Include="Data\SourceBindingEndpoint.cs" />

src/Markup/Perspex.Markup.Xaml/PerspexXamlLoader.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Reflection;
+using System.Text;
 using OmniXaml;
 using Perspex.Markup.Xaml.Context;
 using Perspex.Platform;
@@ -39,6 +40,8 @@ namespace Perspex.Markup.Xaml
         /// <param name="obj">The object to load the XAML into.</param>
         public static void Load(object obj)
         {
+            Contract.Requires<ArgumentNullException>(obj != null);
+
             var loader = new PerspexXamlLoader();
             loader.Load(obj.GetType(), obj);
         }
@@ -53,6 +56,8 @@ namespace Perspex.Markup.Xaml
         /// <returns>The loaded object.</returns>
         public object Load(Type type, object rootInstance = null)
         {
+            Contract.Requires<ArgumentNullException>(type != null);
+
             // HACK: Currently Visual Studio is forcing us to change the extension of xaml files
             // in certain situations, so we try to load .xaml and if that's not found we try .paml.
             // Ideally we'd be able to use .xaml everywhere
@@ -85,6 +90,8 @@ namespace Perspex.Markup.Xaml
         /// <returns>The loaded object.</returns>
         public object Load(Uri uri, object rootInstance = null)
         {
+            Contract.Requires<ArgumentNullException>(uri != null);
+
             var assetLocator = PerspexLocator.Current.GetService<IAssetLoader>();
 
             if (assetLocator == null)
@@ -99,6 +106,24 @@ namespace Perspex.Markup.Xaml
             }
         }
 
+        /// <summary>
+        /// Loads XAML from a string.
+        /// </summary>
+        /// <param name="xaml">The string containing the XAML.</param>
+        /// <param name="rootInstance">
+        /// The optional instance into which the XAML should be loaded.
+        /// </param>
+        /// <returns>The loaded object.</returns>
+        public object Load(string xaml, object rootInstance = null)
+        {
+            Contract.Requires<ArgumentNullException>(xaml != null);
+
+            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(xaml)))
+            {
+                return Load(stream, rootInstance);
+            }
+        }
+
         /// <summary>
         /// Gets the URI for a type.
         /// </summary>

src/Markup/Perspex.Markup.Xaml/Templates/TreeDataTemplate.cs

@@ -4,8 +4,10 @@
 using System;
 using System.Collections;
 using System.Reactive.Linq;
+using System.Reflection;
 using Perspex.Controls;
 using Perspex.Controls.Templates;
+using Perspex.Data;
 using Perspex.Markup.Data;
 using Perspex.Markup.Xaml.Data;
 using Perspex.Metadata;
@@ -19,16 +21,19 @@ namespace Perspex.Markup.Xaml.Templates
         [Content]
         public TemplateContent Content { get; set; }
 
+        [AssignBinding]
         public Binding ItemsSource { get; set; }
 
         public bool Match(object data)
         {
             if (DataType == null)
             {
-                throw new InvalidOperationException("DataTemplate must have a DataType.");
+                return true;
+            }
+            else
+            {
+                return DataType.GetTypeInfo().IsAssignableFrom(data.GetType().GetTypeInfo());
             }
-
-            return DataType == data.GetType();
         }
 
         public IEnumerable ItemsSelector(object item)

src/Perspex.Animation/Animatable.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System.Linq;
+using Perspex.Data;
 
 namespace Perspex.Animation
 {

src/Perspex.Animation/Animate.cs

@@ -5,6 +5,7 @@ using System;
 using System.Diagnostics;
 using System.Linq;
 using System.Reactive.Linq;
+using Perspex.Data;
 using Perspex.Threading;
 
 namespace Perspex.Animation
@@ -96,7 +97,7 @@ namespace Perspex.Animation
         /// <param name="duration">The duration of the animation.</param>
         /// <returns>An <see cref="Animation"/> that can be used to track or stop the animation.</returns>
         public static Animation Property(
-            IObservablePropertyBag target,
+            IPerspexObject target,
             PerspexProperty property,
             object start,
             object finish,
@@ -119,7 +120,7 @@ namespace Perspex.Animation
         /// <param name="duration">The duration of the animation.</param>
         /// <returns>An <see cref="Animation"/> that can be used to track or stop the animation.</returns>
         public static Animation<T> Property<T>(
-            IObservablePropertyBag target,
+            IPerspexObject target,
             PerspexProperty<T> property,
             T start,
             T finish,

src/Perspex.Base/Data/AssignBindingAttribute.cs

@@ -0,0 +1,20 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+
+namespace Perspex.Data
+{
+    /// <summary>
+    /// Signifies that a binding can be assigned to a property.
+    /// </summary>
+    /// <remarks>
+    /// Usually in markup, when a binding is set for a property that property will be bound. 
+    /// Applying this attribute to a property indicates that the binding should be assigned to 
+    /// the property rather than bound.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Property)]
+    public sealed class AssignBindingAttribute : Attribute
+    {
+    }
+}

src/Perspex.Base/Data/BindingMode.cs

@@ -0,0 +1,36 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+namespace Perspex.Data
+{
+    /// <summary>
+    /// Defines possible binding modes.
+    /// </summary>
+    public enum BindingMode
+    {
+        /// <summary>
+        /// Uses the default binding mode specified for the property.
+        /// </summary>
+        Default,
+
+        /// <summary>
+        /// Binds one way from source to target.
+        /// </summary>
+        OneWay,
+
+        /// <summary>
+        /// Binds two-way with the initial value coming from the target.
+        /// </summary>
+        TwoWay,
+
+        /// <summary>
+        /// Updates the target when the application starts or when the data context changes.
+        /// </summary>
+        OneTime,
+
+        /// <summary>
+        /// Binds one way from target to source.
+        /// </summary>
+        OneWayToSource,
+    }
+}

src/Perspex.Base/BindingPriority.cs → src/Perspex.Base/Data/BindingPriority.cs

@@ -1,7 +1,7 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
-namespace Perspex
+namespace Perspex.Data
 {
     /// <summary>
     /// The priority of a binding.

src/Perspex.Base/Data/IBinding.cs

@@ -0,0 +1,33 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System.Reactive.Subjects;
+
+namespace Perspex.Data
+{
+    /// <summary>
+    /// Holds a binding that can be applied to a property on an object.
+    /// </summary>
+    public interface IBinding
+    {
+        /// <summary>
+        /// Gets the binding mode.
+        /// </summary>
+        BindingMode Mode { get; }
+
+        /// <summary>
+        /// Gets the binding priority.
+        /// </summary>
+        BindingPriority Priority { get; }
+
+        /// <summary>
+        /// Creates a subject that can be used to get and set the value of the binding.
+        /// </summary>
+        /// <param name="target">The target instance.</param>
+        /// <param name="targetProperty">The target property. May be null.</param>
+        /// <returns>An <see cref="ISubject{Object}"/>.</returns>
+        ISubject<object> CreateSubject(
+            IPerspexObject target, 
+            PerspexProperty targetProperty);
+    }
+}

src/Perspex.Base/BindingDescriptor.cs → src/Perspex.Base/Data/IndexerDescriptor.cs

@@ -4,43 +4,12 @@
 using System;
 using System.Reactive;
 
-namespace Perspex
+namespace Perspex.Data
 {
     /// <summary>
-    /// Defines possible binding modes.
+    /// Holds a description of a binding for <see cref="PerspexObject"/>'s [] operator.
     /// </summary>
-    public enum BindingMode
+    public class IndexerDescriptor : ObservableBase<object>, IDescription
-    {
-        /// <summary>
-        /// Uses the default binding mode specified for the property.
-        /// </summary>
-        Default,
-
-        /// <summary>
-        /// Binds one way from source to target.
-        /// </summary>
-        OneWay,
-
-        /// <summary>
-        /// Binds two-way with the initial value coming from the target.
-        /// </summary>
-        TwoWay,
-
-        /// <summary>
-        /// Updates the target when the application starts or when the data context changes.
-        /// </summary>
-        OneTime,
-
-        /// <summary>
-        /// Binds one way from target to source.
-        /// </summary>
-        OneWayToSource,
-    }
-
-    /// <summary>
-    /// Holds a description of a binding, usually for <see cref="PerspexObject"/>'s [] operator.
-    /// </summary>
-    public class BindingDescriptor : ObservableBase<object>, IDescription
     {
         /// <summary>
         /// Gets or sets the binding mode.
@@ -100,7 +69,7 @@ namespace Perspex
         /// </summary>
         /// <param name="binding">The current binding.</param>
         /// <returns>A two-way binding.</returns>
-        public static BindingDescriptor operator !(BindingDescriptor binding)
+        public static IndexerDescriptor operator !(IndexerDescriptor binding)
         {
             return binding.WithMode(BindingMode.TwoWay);
         }
@@ -110,7 +79,7 @@ namespace Perspex
         /// </summary>
         /// <param name="binding">The current binding.</param>
         /// <returns>A two-way binding.</returns>
-        public static BindingDescriptor operator ~(BindingDescriptor binding)
+        public static IndexerDescriptor operator ~(IndexerDescriptor binding)
         {
             return binding.WithMode(BindingMode.TwoWay);
         }
@@ -120,7 +89,7 @@ namespace Perspex
         /// </summary>
         /// <param name="mode">The binding mode.</param>
         /// <returns>The object that the method was called on.</returns>
-        public BindingDescriptor WithMode(BindingMode mode)
+        public IndexerDescriptor WithMode(BindingMode mode)
         {
             Mode = mode;
             return this;
@@ -131,7 +100,7 @@ namespace Perspex
         /// </summary>
         /// <param name="priority">The binding priority.</param>
         /// <returns>The object that the method was called on.</returns>
-        public BindingDescriptor WithPriority(BindingPriority priority)
+        public IndexerDescriptor WithPriority(BindingPriority priority)
         {
             Priority = priority;
             return this;

src/Perspex.Base/Diagnostics/PerspexObjectExtensions.cs

@@ -1,6 +1,8 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Perspex.Data;
+
 namespace Perspex.Diagnostics
 {
     /// <summary>

src/Perspex.Base/Diagnostics/PerspexPropertyValue.cs

@@ -1,6 +1,8 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Perspex.Data;
+
 namespace Perspex.Diagnostics
 {
     /// <summary>

src/Perspex.Base/IObservablePropertyBag.cs

@@ -1,95 +0,0 @@
-// Copyright (c) The Perspex Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System;
-using System.Reactive.Subjects;
-
-namespace Perspex
-{
-    /// <summary>
-    /// Interface for getting/setting <see cref="PerspexProperty"/> bindings on an object.
-    /// </summary>
-    public interface IObservablePropertyBag : IPropertyBag
-    {
-        /// <summary>
-        /// Binds a <see cref="PerspexProperty"/> to an observable.
-        /// </summary>
-        /// <param name="property">The property.</param>
-        /// <param name="source">The observable.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        IDisposable Bind(
-            PerspexProperty property,
-            IObservable<object> source,
-            BindingPriority priority = BindingPriority.LocalValue);
-
-        /// <summary>
-        /// Binds a <see cref="PerspexProperty"/> to an observable.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <param name="source">The observable.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        IDisposable Bind<T>(
-            PerspexProperty<T> property,
-            IObservable<T> source,
-            BindingPriority priority = BindingPriority.LocalValue);
-
-        /// <summary>
-        /// Initiates a two-way binding between <see cref="PerspexProperty"/>s.
-        /// </summary>
-        /// <param name="property">The property on this object.</param>
-        /// <param name="source">The source object.</param>
-        /// <param name="sourceProperty">The property on the source object.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        /// <remarks>
-        /// The binding is first carried out from <paramref name="source"/> to this.
-        /// </remarks>
-        IDisposable BindTwoWay(
-            PerspexProperty property,
-            PerspexObject source,
-            PerspexProperty sourceProperty,
-            BindingPriority priority = BindingPriority.LocalValue);
-
-        /// <summary>
-        /// Initiates a two-way binding between a <see cref="PerspexProperty"/> and an 
-        /// <see cref="ISubject{Object}"/>.
-        /// </summary>
-        /// <param name="property">The property on this object.</param>
-        /// <param name="source">The subject to bind to.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        /// <remarks>
-        /// The binding is first carried out from <paramref name="source"/> to this.
-        /// </remarks>
-        IDisposable BindTwoWay(
-            PerspexProperty property,
-            ISubject<object> source,
-            BindingPriority priority = BindingPriority.LocalValue);
-
-        /// <summary>
-        /// Gets an observable for a <see cref="PerspexProperty"/>.
-        /// </summary>
-        /// <param name="property">The property.</param>
-        /// <returns>An observable.</returns>
-        IObservable<object> GetObservable(PerspexProperty property);
-
-        /// <summary>
-        /// Gets an observable for a <see cref="PerspexProperty"/>.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <returns>An observable.</returns>
-        IObservable<T> GetObservable<T>(PerspexProperty<T> property);
-    }
-}

src/Perspex.Base/IPropertyBag.cs → src/Perspex.Base/IPerspexObject.cs

@@ -1,23 +1,20 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System;
+using Perspex.Data;
+
 namespace Perspex
 {
     /// <summary>
     /// Interface for getting/setting <see cref="PerspexProperty"/> values on an object.
     /// </summary>
-    public interface IPropertyBag
+    public interface IPerspexObject
     {
         /// <summary>
-        /// Gets the object that inherited <see cref="PerspexProperty"/> values are inherited from.
+        /// Raised when a <see cref="PerspexProperty"/> value changes on this object.
         /// </summary>
-        IPropertyBag InheritanceParent { get; }
+        event EventHandler<PerspexPropertyChangedEventArgs> PropertyChanged;
-
-        /// <summary>
-        /// Clears a <see cref="PerspexProperty"/>'s local value.
-        /// </summary>
-        /// <param name="property">The property.</param>
-        void ClearValue(PerspexProperty property);
 
         /// <summary>
         /// Gets a <see cref="PerspexProperty"/> value.
@@ -34,13 +31,6 @@ namespace Perspex
         /// <returns>The value.</returns>
         T GetValue<T>(PerspexProperty<T> property);
 
-        /// <summary>
-        /// Checks whether a <see cref="PerspexProperty"/> is registered on this object.
-        /// </summary>
-        /// <param name="property">The property.</param>
-        /// <returns>True if the property is registered, otherwise false.</returns>
-        bool IsRegistered(PerspexProperty property);
-
         /// <summary>
         /// Checks whether a <see cref="PerspexProperty"/> is set on this object.
         /// </summary>
@@ -54,7 +44,10 @@ namespace Perspex
         /// <param name="property">The property.</param>
         /// <param name="value">The value.</param>
         /// <param name="priority">The priority of the value.</param>
-        void SetValue(PerspexProperty property, object value, BindingPriority priority = BindingPriority.LocalValue);
+        void SetValue(
+            PerspexProperty property, 
+            object value, 
+            BindingPriority priority = BindingPriority.LocalValue);
 
         /// <summary>
         /// Sets a <see cref="PerspexProperty"/> value.
@@ -63,6 +56,38 @@ namespace Perspex
         /// <param name="property">The property.</param>
         /// <param name="value">The value.</param>
         /// <param name="priority">The priority of the value.</param>
-        void SetValue<T>(PerspexProperty<T> property, T value, BindingPriority priority = BindingPriority.LocalValue);
+        void SetValue<T>(
+            PerspexProperty<T> property,
+            T value,
+            BindingPriority priority = BindingPriority.LocalValue);
+
+        /// <summary>
+        /// Binds a <see cref="PerspexProperty"/> to an observable.
+        /// </summary>
+        /// <param name="property">The property.</param>
+        /// <param name="source">The observable.</param>
+        /// <param name="priority">The priority of the binding.</param>
+        /// <returns>
+        /// A disposable which can be used to terminate the binding.
+        /// </returns>
+        IDisposable Bind(
+            PerspexProperty property,
+            IObservable<object> source,
+            BindingPriority priority = BindingPriority.LocalValue);
+
+        /// <summary>
+        /// Binds a <see cref="PerspexProperty"/> to an observable.
+        /// </summary>
+        /// <typeparam name="T">The type of the property.</typeparam>
+        /// <param name="property">The property.</param>
+        /// <param name="source">The observable.</param>
+        /// <param name="priority">The priority of the binding.</param>
+        /// <returns>
+        /// A disposable which can be used to terminate the binding.
+        /// </returns>
+        IDisposable Bind<T>(
+            PerspexProperty<T> property,
+            IObservable<T> source,
+            BindingPriority priority = BindingPriority.LocalValue);
     }
 }

src/Perspex.Base/Perspex.Base.csproj

@@ -42,11 +42,13 @@
     <Compile Include="..\Shared\SharedAssemblyInfo.cs">
       <Link>Properties\SharedAssemblyInfo.cs</Link>
     </Compile>
-    <Compile Include="BindingDescriptor.cs" />
+    <Compile Include="Data\AssignBindingAttribute.cs" />
+    <Compile Include="Data\IBinding.cs" />
+    <Compile Include="Data\IndexerDescriptor.cs" />
     <Compile Include="Collections\PerspexDictionary.cs" />
+    <Compile Include="Data\BindingMode.cs" />
     <Compile Include="Diagnostics\PerspexObjectExtensions.cs" />
-    <Compile Include="IObservablePropertyBag.cs" />
+    <Compile Include="IPerspexObject.cs" />
-    <Compile Include="IPropertyBag.cs" />
     <Compile Include="Metadata\ContentAttribute.cs" />
     <Compile Include="PerspexDisposable.cs" />
     <Compile Include="PerspexLocator.cs" />
@@ -56,7 +58,7 @@
     <Compile Include="PerspexProperty`1.cs" />
     <Compile Include="Platform\IAssetLoader.cs" />
     <Compile Include="Platform\IPclPlatformWrapper.cs" />
-    <Compile Include="BindingPriority.cs" />
+    <Compile Include="Data\BindingPriority.cs" />
     <Compile Include="PriorityBindingEntry.cs" />
     <Compile Include="Collections\IPerspexList.cs" />
     <Compile Include="Collections\PerspexList.cs" />
@@ -74,6 +76,8 @@
     <Compile Include="PriorityLevel.cs" />
     <Compile Include="PriorityValue.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="Reactive\AnonymousSubject`1.cs" />
+    <Compile Include="Reactive\AnonymousSubject`2.cs" />
     <Compile Include="Reactive\PerspexObservable.cs" />
     <Compile Include="Threading\Dispatcher.cs" />
     <Compile Include="Threading\DispatcherPriority.cs" />

src/Perspex.Base/PerspexObject.cs

@@ -8,8 +8,7 @@ using System.Linq;
 using System.Reactive.Disposables;
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
-using System.Reflection;
+using Perspex.Data;
-using Perspex.Reactive;
 using Perspex.Threading;
 using Perspex.Utilities;
 using Serilog;
@@ -23,7 +22,7 @@ namespace Perspex
     /// <remarks>
     /// This class is analogous to DependencyObject in WPF.
     /// </remarks>
-    public class PerspexObject : IObservablePropertyBag, INotifyPropertyChanged
+    public class PerspexObject : IPerspexObject, INotifyPropertyChanged
     {
         /// <summary>
         /// The parent object that inherited values are inherited from.
@@ -89,11 +88,6 @@ namespace Perspex
             remove { _inpcChanged -= value; }
         }
 
-        /// <summary>
-        /// Gets the object that inherited <see cref="PerspexProperty"/> values are inherited from.
-        /// </summary>
-        IPropertyBag IPropertyBag.InheritanceParent => InheritanceParent;
-
         /// <summary>
         /// Gets or sets the parent object that inherited <see cref="PerspexProperty"/> values
         /// are inherited from.
@@ -159,7 +153,7 @@ namespace Perspex
         /// Gets or sets a binding for a <see cref="PerspexProperty"/>.
         /// </summary>
         /// <param name="binding">The binding information.</param>
-        public IObservable<object> this[BindingDescriptor binding]
+        public IObservable<object> this[IndexerDescriptor binding]
         {
             get
             {
@@ -171,7 +165,7 @@ namespace Perspex
                 var mode = (binding.Mode == BindingMode.Default) ?
                     binding.Property.DefaultBindingMode :
                     binding.Mode;
-                var sourceBinding = value as BindingDescriptor;
+                var sourceBinding = value as IndexerDescriptor;
 
                 if (sourceBinding == null && mode > BindingMode.OneWay)
                 {
@@ -188,18 +182,19 @@ namespace Perspex
                         SetValue(binding.Property, sourceBinding.Source.GetValue(sourceBinding.Property), binding.Priority);
                         break;
                     case BindingMode.OneWayToSource:
-                        sourceBinding.Source.Bind(sourceBinding.Property, GetObservable(binding.Property), binding.Priority);
+                        sourceBinding.Source.Bind(sourceBinding.Property, this.GetObservable(binding.Property), binding.Priority);
                         break;
                     case BindingMode.TwoWay:
-                        BindTwoWay(binding.Property, sourceBinding.Source, sourceBinding.Property);
+                        var subject = sourceBinding.Source.GetSubject(sourceBinding.Property, sourceBinding.Priority);
+                        this.Bind(binding.Property, subject, BindingMode.TwoWay, sourceBinding.Priority);
                         break;
                 }
             }
         }
 
-        protected virtual BindingDescriptor CreateBindingDescriptor(BindingDescriptor source)
+        protected virtual IndexerDescriptor CreateBindingDescriptor(IndexerDescriptor source)
         {
-            return new BindingDescriptor
+            return new IndexerDescriptor
             {
                 Mode = source.Mode,
                 Priority = source.Priority,
@@ -223,81 +218,6 @@ namespace Perspex
             SetValue(property, PerspexProperty.UnsetValue);
         }
 
-        /// <summary>
-        /// Gets an observable for a <see cref="PerspexProperty"/>.
-        /// </summary>
-        /// <param name="property">The property.</param>
-        /// <returns>An observable.</returns>
-        public IObservable<object> GetObservable(PerspexProperty property)
-        {
-            Contract.Requires<ArgumentNullException>(property != null);
-
-            return new PerspexObservable<object>(
-                observer =>
-                {
-                    EventHandler<PerspexPropertyChangedEventArgs> handler = (s, e) =>
-                    {
-                        if (e.Property == property)
-                        {
-                            observer.OnNext(e.NewValue);
-                        }
-                    };
-
-                    observer.OnNext(GetValue(property));
-
-                    PropertyChanged += handler;
-
-                    return Disposable.Create(() =>
-                    {
-                        PropertyChanged -= handler;
-                    });
-                },
-                GetDescription(property));
-        }
-
-        /// <summary>
-        /// Gets an observable for a <see cref="PerspexProperty"/>.
-        /// </summary>
-        /// <typeparam name="T">The property type.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <returns>An observable.</returns>
-        public IObservable<T> GetObservable<T>(PerspexProperty<T> property)
-        {
-            Contract.Requires<ArgumentNullException>(property != null);
-
-            return GetObservable((PerspexProperty)property).Cast<T>();
-        }
-
-        /// <summary>
-        /// Gets an observable for a <see cref="PerspexProperty"/>.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <returns>An observable which when subscribed pushes the old and new values of the
-        /// property each time it is changed.</returns>
-        public IObservable<Tuple<T, T>> GetObservableWithHistory<T>(PerspexProperty<T> property)
-        {
-            return new PerspexObservable<Tuple<T, T>>(
-                observer =>
-                {
-                    EventHandler<PerspexPropertyChangedEventArgs> handler = (s, e) =>
-                    {
-                        if (e.Property == property)
-                        {
-                            observer.OnNext(Tuple.Create((T)e.OldValue, (T)e.NewValue));
-                        }
-                    };
-
-                    PropertyChanged += handler;
-
-                    return Disposable.Create(() =>
-                    {
-                        PropertyChanged -= handler;
-                    });
-                },
-                GetDescription(property));
-        }
-
         /// <summary>
         /// Gets a <see cref="PerspexProperty"/> value.
         /// </summary>
@@ -561,67 +481,6 @@ namespace Perspex
             }
         }
 
-        /// <summary>
-        /// Initiates a two-way binding between <see cref="PerspexProperty"/>s.
-        /// </summary>
-        /// <param name="property">The property on this object.</param>
-        /// <param name="source">The source object.</param>
-        /// <param name="sourceProperty">The property on the source object.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        /// <remarks>
-        /// The binding is first carried out from <paramref name="source"/> to this.
-        /// </remarks>
-        public IDisposable BindTwoWay(
-            PerspexProperty property,
-            PerspexObject source,
-            PerspexProperty sourceProperty,
-            BindingPriority priority = BindingPriority.LocalValue)
-        {
-            VerifyAccess();
-            _propertyLog.Verbose(
-                "Bound two way {Property} to {Binding} with priority {Priority}",
-                property,
-                source,
-                priority);
-
-            return new CompositeDisposable(
-                Bind(property, source.GetObservable(sourceProperty)),
-                source.Bind(sourceProperty, GetObservable(property)));
-        }
-
-        /// <summary>
-        /// Initiates a two-way binding between a <see cref="PerspexProperty"/> and an 
-        /// <see cref="ISubject{Object}"/>.
-        /// </summary>
-        /// <param name="property">The property on this object.</param>
-        /// <param name="source">The subject to bind to.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        /// <remarks>
-        /// The binding is first carried out from <paramref name="source"/> to this.
-        /// </remarks>
-        public IDisposable BindTwoWay(
-            PerspexProperty property,
-            ISubject<object> source,
-            BindingPriority priority = BindingPriority.LocalValue)
-        {
-            VerifyAccess();
-            _propertyLog.Verbose(
-                "Bound two way {Property} to {Binding} with priority {Priority}",
-                property,
-                GetDescription(source),
-                priority);
-
-            return new CompositeDisposable(
-                Bind(property, source),
-                GetObservable(property).Subscribe(source));
-        }
-
         /// <summary>
         /// Forces the specified property to be revalidated.
         /// </summary>
@@ -638,11 +497,6 @@ namespace Perspex
         }
 
         /// <inheritdoc/>
-        bool IPropertyBag.IsRegistered(PerspexProperty property)
-        {
-            return PerspexPropertyRegistry.Instance.IsRegistered(this, property);
-        }
-
         /// <summary>
         /// Gets all priority values set on the object.
         /// </summary>

src/Perspex.Base/PerspexObjectExtensions.cs

@@ -2,8 +2,12 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
-using System.Linq;
+using System.Reactive;
+using System.Reactive.Disposables;
 using System.Reactive.Linq;
+using System.Reactive.Subjects;
+using Perspex.Data;
+using Perspex.Reactive;
 
 namespace Perspex
 {
@@ -12,6 +16,192 @@ namespace Perspex
     /// </summary>
     public static class PerspexObjectExtensions
     {
+        /// <summary>
+        /// Gets an observable for a <see cref="PerspexProperty"/>.
+        /// </summary>
+        /// <param name="o">The object.</param>
+        /// <param name="property">The property.</param>
+        /// <returns>An observable.</returns>
+        public static IObservable<object> GetObservable(this IPerspexObject o, PerspexProperty property)
+        {
+            Contract.Requires<ArgumentNullException>(o != null);
+            Contract.Requires<ArgumentNullException>(property != null);
+
+            return new PerspexObservable<object>(
+                observer =>
+                {
+                    EventHandler<PerspexPropertyChangedEventArgs> handler = (s, e) =>
+                    {
+                        if (e.Property == property)
+                        {
+                            observer.OnNext(e.NewValue);
+                        }
+                    };
+
+                    observer.OnNext(o.GetValue(property));
+
+                    o.PropertyChanged += handler;
+
+                    return Disposable.Create(() =>
+                    {
+                        o.PropertyChanged -= handler;
+                    });
+                },
+                GetDescription(o, property));
+        }
+
+        /// <summary>
+        /// Gets an observable for a <see cref="PerspexProperty"/>.
+        /// </summary>
+        /// <param name="o">The object.</param>
+        /// <typeparam name="T">The property type.</typeparam>
+        /// <param name="property">The property.</param>
+        /// <returns>An observable.</returns>
+        public static IObservable<T> GetObservable<T>(this IPerspexObject o, PerspexProperty<T> property)
+        {
+            Contract.Requires<ArgumentNullException>(o != null);
+            Contract.Requires<ArgumentNullException>(property != null);
+
+            return o.GetObservable((PerspexProperty)property).Cast<T>();
+        }
+
+        /// <summary>
+        /// Gets an observable for a <see cref="PerspexProperty"/>.
+        /// </summary>
+        /// <param name="o">The object.</param>
+        /// <typeparam name="T">The type of the property.</typeparam>
+        /// <param name="property">The property.</param>
+        /// <returns>
+        /// An observable which when subscribed pushes the old and new values of the property each
+        /// time it is changed.
+        /// </returns>
+        public static IObservable<Tuple<T, T>> GetObservableWithHistory<T>(
+            this IPerspexObject o, 
+            PerspexProperty<T> property)
+        {
+            Contract.Requires<ArgumentNullException>(o != null);
+            Contract.Requires<ArgumentNullException>(property != null);
+
+            return new PerspexObservable<Tuple<T, T>>(
+                observer =>
+                {
+                    EventHandler<PerspexPropertyChangedEventArgs> handler = (s, e) =>
+                    {
+                        if (e.Property == property)
+                        {
+                            observer.OnNext(Tuple.Create((T)e.OldValue, (T)e.NewValue));
+                        }
+                    };
+
+                    o.PropertyChanged += handler;
+
+                    return Disposable.Create(() =>
+                    {
+                        o.PropertyChanged -= handler;
+                    });
+                },
+                GetDescription(o, property));
+        }
+
+        /// <summary>
+        /// Gets a subject for a <see cref="PerspexProperty"/>.
+        /// </summary>
+        /// <param name="o">The object.</param>
+        /// <param name="property">The property.</param>
+        /// <param name="priority">
+        /// The priority with which binding values are written to the object.
+        /// </param>
+        /// <returns>
+        /// An <see cref="ISubject{Object}"/> which can be used for two-way binding to/from the 
+        /// property.
+        /// </returns>
+        public static ISubject<object> GetSubject(
+            this IPerspexObject o,
+            PerspexProperty property,
+            BindingPriority priority = BindingPriority.LocalValue)
+        {
+            // TODO: Subject.Create<T> is not yet in stable Rx : once it is, remove the 
+            // AnonymousSubject classes and use Subject.Create<T>.
+            var output = new Subject<object>();
+            var result = new AnonymousSubject<object>(
+                Observer.Create<object>(
+                    x => output.OnNext(x),
+                    e => output.OnError(e),
+                    () => output.OnCompleted()),
+                o.GetObservable(property));
+            o.Bind(property, output, priority);
+            return result;
+        }
+
+        /// <summary>
+        /// Gets a subject for a <see cref="PerspexProperty"/>.
+        /// </summary>
+        /// <typeparam name="T">The property type.</typeparam>
+        /// <param name="o">The object.</param>
+        /// <param name="property">The property.</param>
+        /// <param name="priority">
+        /// The priority with which binding values are written to the object.
+        /// </param>
+        /// <returns>
+        /// An <see cref="ISubject{T}"/> which can be used for two-way binding to/from the 
+        /// property.
+        /// </returns>
+        public static ISubject<T> GetSubject<T>(
+            this IPerspexObject o,
+            PerspexProperty<T> property,
+            BindingPriority priority = BindingPriority.LocalValue)
+        {
+            // TODO: Subject.Create<T> is not yet in stable Rx : once it is, remove the 
+            // AnonymousSubject classes from this file and use Subject.Create<T>.
+            var output = new Subject<T>();
+            var result = new AnonymousSubject<T>(
+                Observer.Create<T>(
+                    x => output.OnNext(x),
+                    e => output.OnError(e),
+                    () => output.OnCompleted()),
+                o.GetObservable(property));
+            o.Bind(property, output, priority);
+            return result;
+        }
+
+        /// <summary>
+        /// Binds a property to a subject according to a <see cref="BindingMode"/>.
+        /// </summary>
+        /// <param name="o">The object.</param>
+        /// <param name="property">The property to bind.</param>
+        /// <param name="source">The binding source.</param>
+        /// <param name="mode">The binding mode.</param>
+        /// <param name="priority">The binding priority.</param>
+        /// <returns>An <see cref="IDisposable"/> which can be used to cancel the binding.</returns>
+        public static IDisposable Bind(
+            this IPerspexObject o, 
+            PerspexProperty property,
+            ISubject<object> source,
+            BindingMode mode,
+            BindingPriority priority = BindingPriority.LocalValue)
+        {
+            Contract.Requires<ArgumentNullException>(o != null);
+            Contract.Requires<ArgumentNullException>(property != null);
+            Contract.Requires<ArgumentNullException>(source != null);
+
+            switch (mode)
+            {
+                case BindingMode.Default:
+                case BindingMode.OneWay:
+                    return o.Bind(property, source, priority);
+                case BindingMode.TwoWay:
+                    return new CompositeDisposable(
+                        o.Bind(property, source, priority),
+                        o.GetObservable(property).Subscribe(source));
+                case BindingMode.OneTime:
+                    return source.Take(1).Subscribe(x => o.SetValue(property, x, priority));
+                case BindingMode.OneWayToSource:
+                    return o.GetObservable(property).Subscribe(source);
+                default:
+                    throw new ArgumentException("Invalid binding mode.");
+            }
+        }
+
         /// <summary>
         /// Subscribes to a property changed notifications for changes that originate from a
         /// <typeparamref name="TTarget"/>.
@@ -52,6 +242,17 @@ namespace Perspex
             return observable.Subscribe(e => SubscribeAdapter(e, handler));
         }
 
+        /// <summary>
+        /// Gets a description of a property that van be used in observables.
+        /// </summary>
+        /// <param name="o">The object.</param>
+        /// <param name="property">The property</param>
+        /// <returns>The description.</returns>
+        private static string GetDescription(IPerspexObject o, PerspexProperty property)
+        {
+            return $"{o.GetType().Name}.{property.Name}";
+        }
+
         /// <summary>
         /// Observer method for <see cref="AddClassHandler{TTarget}(IObservable{PerspexPropertyChangedEventArgs},
         /// Func{TTarget, Action{PerspexPropertyChangedEventArgs}})"/>.

src/Perspex.Base/PerspexProperty.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Reactive.Subjects;
 using System.Reflection;
+using Perspex.Data;
 using Perspex.Utilities;
 
 namespace Perspex
@@ -323,10 +324,10 @@ namespace Perspex
         /// indexer.
         /// </summary>
         /// <param name="property">The property.</param>
-        /// <returns>A <see cref="BindingDescriptor"/> describing the binding.</returns>
+        /// <returns>A <see cref="IndexerDescriptor"/> describing the binding.</returns>
-        public static BindingDescriptor operator !(PerspexProperty property)
+        public static IndexerDescriptor operator !(PerspexProperty property)
         {
-            return new BindingDescriptor
+            return new IndexerDescriptor
             {
                 Priority = BindingPriority.LocalValue,
                 Property = property,
@@ -338,10 +339,10 @@ namespace Perspex
         /// indexer.
         /// </summary>
         /// <param name="property">The property.</param>
-        /// <returns>A <see cref="BindingDescriptor"/> describing the binding.</returns>
+        /// <returns>A <see cref="IndexerDescriptor"/> describing the binding.</returns>
-        public static BindingDescriptor operator ~(PerspexProperty property)
+        public static IndexerDescriptor operator ~(PerspexProperty property)
         {
-            return new BindingDescriptor
+            return new IndexerDescriptor
             {
                 Priority = BindingPriority.TemplatedParent,
                 Property = property,
@@ -557,13 +558,13 @@ namespace Perspex
         /// Returns a binding accessor that can be passed to <see cref="PerspexObject"/>'s []
         /// operator to initiate a binding.
         /// </summary>
-        /// <returns>A <see cref="BindingDescriptor"/>.</returns>
+        /// <returns>A <see cref="IndexerDescriptor"/>.</returns>
         /// <remarks>
         /// The ! and ~ operators are short forms of this.
         /// </remarks>
-        public BindingDescriptor Bind()
+        public IndexerDescriptor Bind()
         {
-            return new BindingDescriptor
+            return new IndexerDescriptor
             {
                 Property = this,
             };

src/Perspex.Base/PerspexPropertyChangedEventArgs.cs

@@ -1,6 +1,8 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Perspex.Data;
+
 namespace Perspex
 {
     /// <summary>

src/Perspex.Base/PerspexProperty`1.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
+using Perspex.Data;
 
 namespace Perspex
 {

src/Perspex.Base/Reactive/AnonymousSubject`1.cs

@@ -0,0 +1,16 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Reactive.Subjects;
+
+namespace Perspex.Reactive
+{
+    public class AnonymousSubject<T> : AnonymousSubject<T, T>, ISubject<T>
+    {
+        public AnonymousSubject(IObserver<T> observer, IObservable<T> observable)
+            : base(observer, observable)
+        {
+        }
+    }
+}

src/Perspex.Base/Reactive/AnonymousSubject`2.cs

@@ -0,0 +1,49 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Reactive.Subjects;
+
+namespace Perspex.Reactive
+{
+    public class AnonymousSubject<T, U> : ISubject<T, U>
+    {
+        private readonly IObserver<T> _observer;
+        private readonly IObservable<U> _observable;
+
+        public AnonymousSubject(IObserver<T> observer, IObservable<U> observable)
+        {
+            _observer = observer;
+            _observable = observable;
+        }
+
+        public void OnCompleted()
+        {
+            _observer.OnCompleted();
+        }
+
+        public void OnError(Exception error)
+        {
+            if (error == null)
+                throw new ArgumentNullException("error");
+
+            _observer.OnError(error);
+        }
+
+        public void OnNext(T value)
+        {
+            _observer.OnNext(value);
+        }
+
+        public IDisposable Subscribe(IObserver<U> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException("observer");
+
+            //
+            // [OK] Use of unsafe Subscribe: non-pretentious wrapping of an observable sequence.
+            //
+            return _observable.Subscribe/*Unsafe*/(observer);
+        }
+    }
+}

src/Perspex.Controls/Control.cs

@@ -11,6 +11,7 @@ using System.Reactive.Subjects;
 using Perspex.Collections;
 using Perspex.Controls.Primitives;
 using Perspex.Controls.Templates;
+using Perspex.Data;
 using Perspex.Input;
 using Perspex.Interactivity;
 using Perspex.LogicalTree;

src/Perspex.Controls/ControlExtensions.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Linq;
+using Perspex.Data;
 using Perspex.LogicalTree;
 using Perspex.Styling;
 
@@ -13,6 +14,36 @@ namespace Perspex.Controls
     /// </summary>
     public static class ControlExtensions
     {
+        /// <summary>
+        /// Binds a property on an <see cref="IControl"/> to an <see cref="IBinding"/>.
+        /// </summary>
+        /// <param name="o">The object.</param>
+        /// <param name="property">The property to bind.</param>
+        /// <param name="binding">The binding.</param>
+        /// <returns>An <see cref="IDisposable"/> which can be used to cancel the binding.</returns>
+        public static IDisposable Bind(
+            this IControl o,
+            PerspexProperty property,
+            IBinding binding)
+        {
+            Contract.Requires<ArgumentNullException>(o != null);
+            Contract.Requires<ArgumentNullException>(property != null);
+            Contract.Requires<ArgumentNullException>(binding != null);
+
+            var mode = binding.Mode;
+
+            if (mode == BindingMode.Default)
+            {
+                mode = property.DefaultBindingMode;
+            }
+
+            return o.Bind(
+                property, 
+                binding.CreateSubject(o, property), 
+                mode,
+                binding.Priority);
+        }
+
         /// <summary>
         /// Tries to being the control into view.
         /// </summary>

src/Perspex.Controls/Generators/TreeItemContainerGenerator.cs

@@ -77,7 +77,6 @@ namespace Perspex.Controls.Generators
 
                 result.SetValue(ContentProperty, template.Build(item));
                 result.SetValue(ItemsProperty, template.ItemsSelector(item));
-                result.SetValue(IsExpandedProperty, template.IsExpanded(item));
 
                 if (!(item is IControl))
                 {

src/Perspex.Controls/Presenters/ScrollContentPresenter.cs

@@ -61,7 +61,7 @@ namespace Perspex.Controls.Presenters
         {
             AddHandler(RequestBringIntoViewEvent, BringIntoViewRequested);
 
-            GetObservable(ChildProperty).Subscribe(ChildChanged);
+            this.GetObservable(ChildProperty).Subscribe(ChildChanged);
         }
 
         /// <summary>
@@ -236,7 +236,7 @@ namespace Perspex.Controls.Presenters
             {
                 scrollable.InvalidateScroll = () => UpdateFromScrollable(scrollable);
                 _scrollableSubscription = new CompositeDisposable(
-                    GetObservable(OffsetProperty).Skip(1).Subscribe(x => scrollable.Offset = x),
+                    this.GetObservable(OffsetProperty).Skip(1).Subscribe(x => scrollable.Offset = x),
                     Disposable.Create(() => scrollable.InvalidateScroll = null));
                 UpdateFromScrollable(scrollable);
             }

src/Perspex.Controls/Presenters/TextPresenter.cs

@@ -33,15 +33,15 @@ namespace Perspex.Controls.Presenters
             _caretTimer.Interval = TimeSpan.FromMilliseconds(500);
             _caretTimer.Tick += CaretTimerTick;
 
-            _canScrollHorizontally = GetObservable(TextWrappingProperty)
+            _canScrollHorizontally = this.GetObservable(TextWrappingProperty)
                 .Select(x => x == TextWrapping.NoWrap);
 
             Observable.Merge(
-                GetObservable(SelectionStartProperty),
+                this.GetObservable(SelectionStartProperty),
-                GetObservable(SelectionEndProperty))
+                this.GetObservable(SelectionEndProperty))
                 .Subscribe(_ => InvalidateFormattedText());
 
-            GetObservable(CaretIndexProperty)
+            this.GetObservable(CaretIndexProperty)
                 .Subscribe(CaretIndexChanged);
         }
 

src/Perspex.Controls/Primitives/AccessText.cs

@@ -37,7 +37,7 @@ namespace Perspex.Controls.Primitives
         /// </summary>
         public AccessText()
         {
-            GetObservable(TextProperty).Subscribe(TextChanged);
+            this.GetObservable(TextProperty).Subscribe(TextChanged);
         }
 
         /// <summary>

src/Perspex.Controls/Primitives/ScrollBar.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Reactive;
 using System.Reactive.Linq;
+using Perspex.Data;
 
 namespace Perspex.Controls.Primitives
 {
@@ -36,10 +37,10 @@ namespace Perspex.Controls.Primitives
         public ScrollBar()
         {
             var isVisible = Observable.Merge(
-                GetObservable(MinimumProperty).Select(_ => Unit.Default),
+                this.GetObservable(MinimumProperty).Select(_ => Unit.Default),
-                GetObservable(MaximumProperty).Select(_ => Unit.Default),
+                this.GetObservable(MaximumProperty).Select(_ => Unit.Default),
-                GetObservable(ViewportSizeProperty).Select(_ => Unit.Default),
+                this.GetObservable(ViewportSizeProperty).Select(_ => Unit.Default),
-                GetObservable(VisibilityProperty).Select(_ => Unit.Default))
+                this.GetObservable(VisibilityProperty).Select(_ => Unit.Default))
                 .Select(_ => CalculateIsVisible());
             Bind(IsVisibleProperty, isVisible, BindingPriority.Style);
         }

src/Perspex.Controls/Primitives/SelectingItemsControl.cs

@@ -8,6 +8,7 @@ using System.Collections.Specialized;
 using System.Linq;
 using Perspex.Collections;
 using Perspex.Controls.Generators;
+using Perspex.Data;
 using Perspex.Input;
 using Perspex.Interactivity;
 using Perspex.Styling;

src/Perspex.Controls/Primitives/TemplatedControl.cs

@@ -6,6 +6,7 @@ using System.Linq;
 using System.Reactive.Linq;
 using Perspex.Controls.Presenters;
 using Perspex.Controls.Templates;
+using Perspex.Data;
 using Perspex.Interactivity;
 using Perspex.Media;
 using Perspex.Styling;
@@ -224,14 +225,14 @@ namespace Perspex.Controls.Primitives
             }
         }
 
-        protected sealed override BindingDescriptor CreateBindingDescriptor(BindingDescriptor source)
+        protected sealed override IndexerDescriptor CreateBindingDescriptor(IndexerDescriptor source)
         {
             var result = base.CreateBindingDescriptor(source);
 
             // If the binding is a template binding, then complete when the Template changes.
             if (source.Priority == BindingPriority.TemplatedParent)
             {
-                var templateChanged = GetObservable(TemplateProperty).Skip(1);
+                var templateChanged = this.GetObservable(TemplateProperty).Skip(1);
 
                 result.SourceObservable = result.Source.GetObservable(result.Property)
                     .TakeUntil(templateChanged);

src/Perspex.Controls/Primitives/ToggleButton.cs

@@ -9,21 +9,22 @@ namespace Perspex.Controls.Primitives
     public class ToggleButton : Button
     {
         public static readonly PerspexProperty<bool> IsCheckedProperty =
-            PerspexProperty.Register<ToggleButton, bool>("IsChecked");
+            PerspexProperty.RegisterDirect<ToggleButton, bool>(
+                "IsChecked",
+                o => o.IsChecked,
+                (o,v) => o.IsChecked = v);
+
+        private bool _isChecked;
 
         static ToggleButton()
         {
             PseudoClass(IsCheckedProperty, ":checked");
         }
 
-        public ToggleButton()
-        {
-        }
-
         public bool IsChecked
         {
-            get { return GetValue(IsCheckedProperty); }
+            get { return _isChecked; }
-            set { SetValue(IsCheckedProperty, value); }
+            set { SetAndRaise(IsCheckedProperty, ref _isChecked, value); }
         }
 
         protected override void OnClick(RoutedEventArgs e)

src/Perspex.Controls/Primitives/Track.cs

@@ -38,7 +38,7 @@ namespace Perspex.Controls.Primitives
 
         public Track()
         {
-            GetObservableWithHistory(ThumbProperty).Subscribe(val =>
+            this.GetObservableWithHistory(ThumbProperty).Subscribe(val =>
             {
                 if (val.Item1 != null)
                 {

src/Perspex.Controls/RadioButton.cs

@@ -12,7 +12,7 @@ namespace Perspex.Controls
     {
         public RadioButton()
         {
-            GetObservable(IsCheckedProperty).Subscribe(IsCheckedChanged);
+            this.GetObservable(IsCheckedProperty).Subscribe(IsCheckedChanged);
         }
 
         protected override void Toggle()

src/Perspex.Controls/ScrollViewer.cs

@@ -135,8 +135,8 @@ namespace Perspex.Controls
         public ScrollViewer()
         {
             var extentAndViewport = Observable.CombineLatest(
-                GetObservable(ExtentProperty),
+                this.GetObservable(ExtentProperty),
-                GetObservable(ViewportProperty))
+                this.GetObservable(ViewportProperty))
                 .Select(x => new { Extent = x[0], Viewport = x[1] });
 
             Bind(
@@ -155,15 +155,15 @@ namespace Perspex.Controls
                 VerticalScrollBarMaximumProperty,
                 extentAndViewport.Select(x => Max(x.Extent.Height - x.Viewport.Height, 0)));
 
-            GetObservable(OffsetProperty).Subscribe(x =>
+            this.GetObservable(OffsetProperty).Subscribe(x =>
             {
                 SetValue(HorizontalScrollBarValueProperty, x.X);
                 SetValue(VerticalScrollBarValueProperty, x.Y);
             });
 
             var scrollBarOffset = Observable.CombineLatest(
-                GetObservable(HorizontalScrollBarValueProperty),
+                this.GetObservable(HorizontalScrollBarValueProperty),
-                GetObservable(VerticalScrollBarValueProperty))
+                this.GetObservable(VerticalScrollBarValueProperty))
                 .Select(x => new Vector(x[0], x[1]))
                 .Subscribe(x => Offset = x);
         }

src/Perspex.Controls/Templates/FuncTreeDataTemplate.cs

@@ -14,8 +14,6 @@ namespace Perspex.Controls.Templates
     {
         private readonly Func<object, IEnumerable> _itemsSelector;
 
-        private readonly Func<object, bool> _isExpanded;
-
         /// <summary>
         /// Initializes a new instance of the <see cref="FuncTreeDataTemplate"/> class.
         /// </summary>
@@ -35,30 +33,6 @@ namespace Perspex.Controls.Templates
         {
         }
 
-        /// <summary>
-        /// Initializes a new instance of the <see cref="FuncTreeDataTemplate"/> class.
-        /// </summary>
-        /// <param name="type">The type of data which the data template matches.</param>
-        /// <param name="build">
-        /// A function which when passed an object of <paramref name="type"/> returns a control.
-        /// </param>
-        /// <param name="itemsSelector">
-        /// A function which when passed an object of <paramref name="type"/> returns the child
-        /// items.
-        /// </param>
-        /// <param name="isExpanded">
-        /// A function which when passed an object of <paramref name="type"/> returns the the
-        /// initial expanded state of the node.
-        /// </param>
-        public FuncTreeDataTemplate(
-            Type type,
-            Func<object, IControl> build,
-            Func<object, IEnumerable> itemsSelector,
-            Func<object, bool> isExpanded)
-            : this(o => IsInstance(o, type), build, itemsSelector, isExpanded)
-        {
-        }
-
         /// <summary>
         /// Initializes a new instance of the <see cref="FuncTreeDataTemplate"/> class.
         /// </summary>
@@ -75,46 +49,9 @@ namespace Perspex.Controls.Templates
             Func<object, bool> match,
             Func<object, IControl> build,
             Func<object, IEnumerable> itemsSelector)
-            : this(match, build, itemsSelector, _ => false)
-        {
-            _itemsSelector = itemsSelector;
-        }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="FuncTreeDataTemplate"/> class.
-        /// </summary>
-        /// <param name="match">
-        /// A function which determines whether the data template matches the specified data.
-        /// </param>
-        /// <param name="build">
-        /// A function which when passed a matching object returns a control.
-        /// </param>
-        /// <param name="itemsSelector">
-        /// A function which when passed a matching object returns the child items.
-        /// </param>
-        /// <param name="isExpanded">
-        /// A function which when passed a matching object returns the the initial expanded state
-        /// of the node.
-        /// </param>
-        public FuncTreeDataTemplate(
-            Func<object, bool> match,
-            Func<object, IControl> build,
-            Func<object, IEnumerable> itemsSelector,
-            Func<object, bool> isExpanded)
             : base(match, build)
         {
             _itemsSelector = itemsSelector;
-            _isExpanded = isExpanded;
-        }
-
-        /// <summary>
-        /// Checks to see if the item should be initially expanded.
-        /// </summary>
-        /// <param name="item">The item.</param>
-        /// <returns>True if the item should be initially expanded, otherwise false.</returns>
-        public bool IsExpanded(object item)
-        {
-            return this?._isExpanded(item) ?? false;
         }
 
         /// <summary>

src/Perspex.Controls/Templates/FuncTreeDataTemplate`1.cs

@@ -32,32 +32,6 @@ namespace Perspex.Controls.Templates
         {
         }
 
-        /// <summary>
-        /// Initializes a new instance of the <see cref="FuncTreeDataTemplate{T}"/> class.
-        /// </summary>
-        /// <param name="build">
-        /// A function which when passed an object of <typeparamref name="T"/> returns a control.
-        /// </param>
-        /// <param name="itemsSelector">
-        /// A function which when passed an object of <typeparamref name="T"/> returns the child
-        /// items.
-        /// </param>
-        /// <param name="isExpanded">
-        /// A function which when passed an object of <typeparamref name="T"/> returns the the
-        /// initial expanded state of the node.
-        /// </param>
-        public FuncTreeDataTemplate(
-            Func<T, Control> build,
-            Func<T, IEnumerable> itemsSelector,
-            Func<T, bool> isExpanded)
-            : base(
-                typeof(T),
-                Cast(build),
-                Cast(itemsSelector),
-                Cast(isExpanded))
-        {
-        }
-
         /// <summary>
         /// Initializes a new instance of the <see cref="FuncTreeDataTemplate{T}"/> class.
         /// </summary>
@@ -81,35 +55,6 @@ namespace Perspex.Controls.Templates
         {
         }
 
-        /// <summary>
-        /// Initializes a new instance of the <see cref="FuncTreeDataTemplate{T}"/> class.
-        /// </summary>
-        /// <param name="match">
-        /// A function which determines whether the data template matches the specified data.
-        /// </param>
-        /// <param name="build">
-        /// A function which when passed a matching object returns a control.
-        /// </param>
-        /// <param name="itemsSelector">
-        /// A function which when passed a matching object returns the child items.
-        /// </param>
-        /// <param name="isExpanded">
-        /// A function which when passed a matching object returns the the initial expanded state
-        /// of the node.
-        /// </param>
-        public FuncTreeDataTemplate(
-            Func<T, bool> match,
-            Func<T, Control> build,
-            Func<T, IEnumerable> itemsSelector,
-            Func<T, bool> isExpanded)
-            : base(
-                CastMatch(match),
-                Cast(build),
-                Cast(itemsSelector),
-                Cast(isExpanded))
-        {
-        }
-
         /// <summary>
         /// Casts a typed match function to an untyped match function.
         /// </summary>

src/Perspex.Controls/Templates/ITreeDataTemplate.cs

@@ -10,13 +10,6 @@ namespace Perspex.Controls.Templates
     /// </summary>
     public interface ITreeDataTemplate : IDataTemplate
     {
-        /// <summary>
-        /// Checks to see if the item should be initially expanded.
-        /// </summary>
-        /// <param name="item">The item.</param>
-        /// <returns>True if the item should be initially expanded, otherwise false.</returns>
-        bool IsExpanded(object item);
-
         /// <summary>
         /// Selects the child items of an item.
         /// </summary>

src/Perspex.Controls/TextBlock.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Reactive;
 using System.Reactive.Linq;
+using Perspex.Data;
 using Perspex.Media;
 using Perspex.Metadata;
 
@@ -106,10 +107,10 @@ namespace Perspex.Controls
         public TextBlock()
         {
             Observable.Merge(
-                GetObservable(TextProperty).Select(_ => Unit.Default),
+                this.GetObservable(TextProperty).Select(_ => Unit.Default),
-                GetObservable(TextAlignmentProperty).Select(_ => Unit.Default),
+                this.GetObservable(TextAlignmentProperty).Select(_ => Unit.Default),
-                GetObservable(FontSizeProperty).Select(_ => Unit.Default),
+                this.GetObservable(FontSizeProperty).Select(_ => Unit.Default),
-                GetObservable(FontStyleProperty).Select(_ => Unit.Default))
+                this.GetObservable(FontStyleProperty).Select(_ => Unit.Default))
                 .Subscribe(_ =>
                 {
                     InvalidateFormattedText();

src/Perspex.Controls/TextBox.cs

@@ -14,6 +14,7 @@ using Perspex.Input;
 using Perspex.Interactivity;
 using Perspex.Media;
 using Perspex.Metadata;
+using Perspex.Data;
 
 namespace Perspex.Controls
 {
@@ -73,7 +74,7 @@ namespace Perspex.Controls
 
         public TextBox()
         {
-            var canScrollHorizontally = GetObservable(AcceptsReturnProperty)
+            var canScrollHorizontally = this.GetObservable(AcceptsReturnProperty)
                 .Select(x => !x);
 
             Bind(
@@ -81,7 +82,7 @@ namespace Perspex.Controls
                 canScrollHorizontally,
                 BindingPriority.Style);
 
-            var horizontalScrollBarVisibility = GetObservable(AcceptsReturnProperty)
+            var horizontalScrollBarVisibility = this.GetObservable(AcceptsReturnProperty)
                 .Select(x => x ? ScrollBarVisibility.Auto : ScrollBarVisibility.Hidden);
 
             Bind(

src/Perspex.Controls/TopLevel.cs

@@ -115,8 +115,8 @@ namespace Perspex.Controls
             _accessKeyHandler?.SetOwner(this);
             styler?.ApplyStyles(this);
 
-            GetObservable(ClientSizeProperty).Skip(1).Subscribe(x => PlatformImpl.ClientSize = x);
+            this.GetObservable(ClientSizeProperty).Skip(1).Subscribe(x => PlatformImpl.ClientSize = x);
-            GetObservable(PointerOverElementProperty)
+            this.GetObservable(PointerOverElementProperty)
                 .Select(
                     x => (x as InputElement)?.GetObservable(CursorProperty) ?? Observable.Empty<Cursor>())
                 .Switch().Subscribe(cursor => PlatformImpl.SetCursor(cursor?.PlatformCursor));

src/Perspex.Diagnostics/Debug.cs

@@ -7,6 +7,7 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Perspex.Controls;
+using Perspex.Data;
 
 namespace Perspex.Diagnostics
 {

src/Perspex.Diagnostics/DevTools.cs

@@ -21,7 +21,7 @@ namespace Perspex.Diagnostics
         public DevTools()
         {
             _viewModel = new DevToolsViewModel();
-            GetObservable(RootProperty).Subscribe(x => _viewModel.Root = x);
+            this.GetObservable(RootProperty).Subscribe(x => _viewModel.Root = x);
 
             InitializeComponent();
         }

src/Perspex.Diagnostics/ViewModels/PropertyDetails.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
+using Perspex.Data;
 using ReactiveUI;
 
 namespace Perspex.Diagnostics.ViewModels

src/Perspex.Diagnostics/Views/ControlDetailsView.cs

@@ -19,7 +19,7 @@ namespace Perspex.Diagnostics.Views
         public ControlDetailsView()
         {
             InitializeComponent();
-            GetObservable(DataContextProperty)
+            this.GetObservable(DataContextProperty)
                 .Subscribe(x => ViewModel = (ControlDetailsViewModel)x);
         }
 

src/Perspex.Diagnostics/Views/LogicalTreeView.cs

@@ -20,7 +20,7 @@ namespace Perspex.Diagnostics.Views
         public LogicalTreeView()
         {
             InitializeComponent();
-            GetObservable(DataContextProperty)
+            this.GetObservable(DataContextProperty)
                 .Subscribe(x => ViewModel = (LogicalTreeViewModel)x);
         }
 

src/Perspex.Diagnostics/Views/VisualTreeView.cs

@@ -21,7 +21,7 @@ namespace Perspex.Diagnostics.Views
         public VisualTreeView()
         {
             InitializeComponent();
-            GetObservable(DataContextProperty)
+            this.GetObservable(DataContextProperty)
                 .Subscribe(x => ViewModel = (VisualTreeViewModel)x);
         }
 

src/Perspex.SceneGraph/Animation/CrossFade.cs

@@ -58,7 +58,7 @@ namespace Perspex.Animation
             if (from != null)
             {
                 tasks.Add(Animate.Property(
-                    (IObservablePropertyBag)from,
+                    (IPerspexObject)from,
                     Visual.OpacityProperty,
                     from.Opacity,
                     0,
@@ -72,7 +72,7 @@ namespace Perspex.Animation
                 to.IsVisible = true;
 
                 tasks.Add(Animate.Property(
-                    (IObservablePropertyBag)to,
+                    (IPerspexObject)to,
                     Visual.OpacityProperty,
                     0,
                     1,

src/Perspex.SceneGraph/Media/MatrixTransform.cs

@@ -21,7 +21,7 @@ namespace Perspex.Media
         /// </summary>
         public MatrixTransform()
         {
-            GetObservable(MatrixProperty).Subscribe(_ => RaiseChanged());
+            this.GetObservable(MatrixProperty).Subscribe(_ => RaiseChanged());
         }
 
         /// <summary>

src/Perspex.SceneGraph/Media/RotateTransform.cs

@@ -21,7 +21,7 @@ namespace Perspex.Media
         /// </summary>
         public RotateTransform()
         {
-            GetObservable(AngleProperty).Subscribe(_ => RaiseChanged());
+            this.GetObservable(AngleProperty).Subscribe(_ => RaiseChanged());
         }
 
         /// <summary>

src/Perspex.SceneGraph/Media/TranslateTransform.cs

@@ -27,8 +27,8 @@ namespace Perspex.Media
         /// </summary>
         public TranslateTransform()
         {
-            GetObservable(XProperty).Subscribe(_ => RaiseChanged());
+            this.GetObservable(XProperty).Subscribe(_ => RaiseChanged());
-            GetObservable(YProperty).Subscribe(_ => RaiseChanged());
+            this.GetObservable(YProperty).Subscribe(_ => RaiseChanged());
         }
 
         /// <summary>

src/Perspex.SceneGraph/Visual.cs

@@ -8,6 +8,7 @@ using System.Linq;
 using System.Reactive.Linq;
 using Perspex.Animation;
 using Perspex.Collections;
+using Perspex.Data;
 using Perspex.Media;
 using Perspex.Platform;
 using Perspex.Rendering;

src/Perspex.Styling/Perspex.Styling.csproj

@@ -45,6 +45,8 @@
     <Compile Include="ILogical.cs" />
     <Compile Include="LogicalTree\LogicalExtensions.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="Styling\ActivatedSubject.cs" />
+    <Compile Include="Styling\ActivatedValue.cs" />
     <Compile Include="Styling\IGlobalStyles.cs" />
     <Compile Include="Styling\ISetter.cs" />
     <Compile Include="Styling\IStyle.cs" />
@@ -56,11 +58,10 @@
     <Compile Include="Styling\SelectorMatch.cs" />
     <Compile Include="Styling\Selector.cs" />
     <Compile Include="Styling\Selectors.cs" />
-    <Compile Include="Styling\ObservableSetter.cs" />
     <Compile Include="Styling\Setter.cs" />
     <Compile Include="Styling\Style.cs" />
     <Compile Include="Styling\StyleActivator.cs" />
-    <Compile Include="Styling\StyleBinding.cs" />
+    <Compile Include="Styling\ActivatedObservable.cs" />
     <Compile Include="Styling\Styler.cs" />
     <Compile Include="Styling\Styles.cs" />
   </ItemGroup>

src/Perspex.Styling/Styling/ActivatedObservable.cs

@@ -0,0 +1,74 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Reactive;
+using System.Reactive.Linq;
+
+namespace Perspex.Styling
+{
+    /// <summary>
+    /// An observable which is switched on or off according to an activator observable.
+    /// </summary>
+    /// <remarks>
+    /// An <see cref="ActivatedObservable"/> has two inputs: an activator observable a 
+    /// <see cref="Source"/> observable which produces the activated value. When the activator 
+    /// produces true, the <see cref="ActivatedObservable"/> will produce the current activated 
+    /// value. When the activator produces false it will produce
+    /// <see cref="PerspexProperty.UnsetValue"/>.
+    /// </remarks>
+    internal class ActivatedObservable : ObservableBase<object>, IDescription
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ActivatedObservable"/> class.
+        /// </summary>
+        /// <param name="activator">The activator.</param>
+        /// <param name="source">An observable that produces the activated value.</param>
+        /// <param name="description">The binding description.</param>
+        public ActivatedObservable(
+            IObservable<bool> activator,
+            IObservable<object> source,
+            string description)
+        {
+            Activator = activator;
+            Description = description;
+            Source = source;
+        }
+
+        /// <summary>
+        /// Gets the activator observable.
+        /// </summary>
+        public IObservable<bool> Activator { get; }
+
+        /// <summary>
+        /// Gets a description of the binding.
+        /// </summary>
+        public string Description { get; }
+
+        /// <summary>
+        /// Gets an observable which produces the <see cref="ActivatedValue"/>.
+        /// </summary>
+        public IObservable<object> Source { get; }
+
+        /// <summary>
+        /// Notifies the provider that an observer is to receive notifications.
+        /// </summary>
+        /// <param name="observer">The observer.</param>
+        /// <returns>IDisposable object used to unsubscribe from the observable sequence.</returns>
+        protected override IDisposable SubscribeCore(IObserver<object> observer)
+        {
+            Contract.Requires<ArgumentNullException>(observer != null);
+
+            var sourceCompleted = Source.TakeLast(1).Select(_ => Unit.Default);
+            var activatorCompleted = Activator.TakeLast(1).Select(_ => Unit.Default);
+            var completed = sourceCompleted.Merge(activatorCompleted);
+
+            return Activator
+                .CombineLatest(Source, (x, y) => new { Active = x, Value = y })
+                .Select(x => x.Active ? x.Value : PerspexProperty.UnsetValue)
+                .DistinctUntilChanged()
+                .TakeUntil(completed)
+                .Subscribe(observer);
+        }
+    }
+}

src/Perspex.Styling/Styling/ActivatedSubject.cs

@@ -0,0 +1,111 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
+
+namespace Perspex.Styling
+{
+    /// <summary>
+    /// A subject which is switched on or off according to an activator observable.
+    /// </summary>
+    /// <remarks>
+    /// An <see cref="ActivatedSubject"/> has two inputs: an activator observable and either an
+    /// <see cref="ActivatedValue"/> or a <see cref="Source"/> observable which produces the
+    /// activated value. When the activator produces true, the <see cref="ActivatedObservable"/> will
+    /// produce the current activated value. When the activator produces false it will produce
+    /// <see cref="PerspexProperty.UnsetValue"/>.
+    /// </remarks>
+    internal class ActivatedSubject : ActivatedObservable, ISubject<object>, IDescription
+    {
+        private bool? _active;
+        private bool _completed;
+        private object _value;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ActivatedSubject"/> class.
+        /// </summary>
+        /// <param name="activator">The activator.</param>
+        /// <param name="source">An observable that produces the activated value.</param>
+        /// <param name="description">The binding description.</param>
+        public ActivatedSubject(
+            IObservable<bool> activator,
+            ISubject<object> source,
+            string description)
+            : base(activator, source, description)
+        {
+            Activator.Subscribe(ActivatorChanged, ActivatorError, ActivatorCompleted);
+        }
+
+        /// <summary>
+        /// Gets the underlying subject.
+        /// </summary>
+        public new ISubject<object> Source
+        {
+            get { return (ISubject<object>)base.Source; }
+        }
+
+        /// <summary>
+        /// Notifies all subscribed observers about the end of the sequence.
+        /// </summary>
+        public void OnCompleted()
+        {
+            if (_active.Value && !_completed)
+            {
+                Source.OnCompleted();
+            }
+        }
+
+        /// <summary>
+        /// Notifies all subscribed observers with the exception.
+        /// </summary>
+        /// <param name="error">The exception to send to all subscribed observers.</param>
+        /// <exception cref="ArgumentNullException"><paramref name="error"/> is null.</exception>
+        public void OnError(Exception error)
+        {
+            if (_active.Value && !_completed)
+            {
+                Source.OnError(error);
+            }
+        }
+
+        /// <summary>
+        /// Notifies all subscribed observers with the value.
+        /// </summary>
+        /// <param name="value">The value to send to all subscribed observers.</param>        
+        public void OnNext(object value)
+        {
+            _value = value;
+
+            if (_active.Value && !_completed)
+            {
+                Source.OnNext(value);
+            }
+        }
+
+        private void ActivatorChanged(bool active)
+        {
+            bool first = !_active.HasValue;
+
+            _active = active;
+
+            if (!first)
+            {
+                Source.OnNext(active ? _value : PerspexProperty.UnsetValue);
+            }
+        }
+
+        private void ActivatorCompleted()
+        {
+            _completed = true;
+            Source.OnCompleted();
+        }
+
+        private void ActivatorError(Exception e)
+        {
+            _completed = true;
+            Source.OnError(e);
+        }
+    }
+}

src/Perspex.Styling/Styling/ActivatedValue.cs

@@ -0,0 +1,72 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Reactive;
+using System.Reactive.Linq;
+
+namespace Perspex.Styling
+{
+    /// <summary>
+    /// An value which is switched on or off according to an activator observable.
+    /// </summary>
+    /// <remarks>
+    /// An <see cref="ActivatedValue"/> has two inputs: an activator observable and an
+    /// <see cref="Value"/>. When the activator produces true, the 
+    /// <see cref="ActivatedValue"/> will produce the current value. When the activator 
+    /// produces false it will produce <see cref="PerspexProperty.UnsetValue"/>.
+    /// </remarks>
+    internal class ActivatedValue : ObservableBase<object>, IDescription
+    {
+        /// <summary>
+        /// The activator.
+        /// </summary>
+        private readonly IObservable<bool> _activator;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ActivatedObservable"/> class.
+        /// </summary>
+        /// <param name="activator">The activator.</param>
+        /// <param name="value">The activated value.</param>
+        /// <param name="description">The binding description.</param>
+        public ActivatedValue(
+            IObservable<bool> activator,
+            object value,
+            string description)
+        {
+            _activator = activator;
+            Value = value;
+            Description = description;
+        }
+
+        /// <summary>
+        /// Gets the activated value.
+        /// </summary>
+        public object Value
+        {
+            get;
+        }
+
+        /// <summary>
+        /// Gets a description of the binding.
+        /// </summary>
+        public string Description
+        {
+            get;
+        }
+
+        /// <summary>
+        /// Notifies the provider that an observer is to receive notifications.
+        /// </summary>
+        /// <param name="observer">The observer.</param>
+        /// <returns>IDisposable object used to unsubscribe from the observable sequence.</returns>
+        protected override IDisposable SubscribeCore(IObserver<object> observer)
+        {
+            Contract.Requires<ArgumentNullException>(observer != null);
+
+            return _activator
+                .Select(active => active ? Value : PerspexProperty.UnsetValue)
+                .Subscribe(observer);
+        }
+    }
+}

src/Perspex.Styling/Styling/IStyleable.cs

@@ -10,7 +10,7 @@ namespace Perspex.Styling
     /// <summary>
     /// Interface for styleable elements.
     /// </summary>
-    public interface IStyleable : IObservablePropertyBag, INamed
+    public interface IStyleable : IPerspexObject, INamed
     {
         /// <summary>
         /// Raised when the control's style should be removed.

src/Perspex.Styling/Styling/ITemplatedControl.cs

@@ -5,14 +5,7 @@ using System;
 
 namespace Perspex.Styling
 {
-    public interface ITemplatedControl
+    public interface ITemplatedControl : IPerspexObject
     {
-        /// <summary>
-        /// Gets an observable for a <see cref="PerspexProperty"/>.
-        /// </summary>
-        /// <typeparam name="T"></typeparam>
-        /// <param name="property">The property to get the observable for.</param>
-        /// <returns>The observable.</returns>
-        IObservable<T> GetObservable<T>(PerspexProperty<T> property);
     }
 }

src/Perspex.Styling/Styling/ObservableSetter.cs

@@ -1,65 +0,0 @@
-// Copyright (c) The Perspex Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System;
-
-namespace Perspex.Styling
-{
-    /// <summary>
-    /// A setter for a <see cref="Style"/> whose source is an observable.
-    /// </summary>
-    /// <remarks>
-    /// A <see cref="Setter"/> is used to set a <see cref="PerspexProperty"/> value on a
-    /// <see cref="PerspexObject"/> depending on a condition.
-    /// </remarks>
-    public class ObservableSetter : ISetter
-    {
-        /// <summary>
-        /// Initializes a new instance of the <see cref="ObservableSetter"/> class.
-        /// </summary>
-        /// <param name="property">The property to set.</param>
-        /// <param name="source">An observable which produces the value for the property.</param>
-        public ObservableSetter(PerspexProperty property, IObservable<object> source)
-        {
-            Property = property;
-            Source = source;
-        }
-
-        /// <summary>
-        /// Gets or sets the property to set.
-        /// </summary>
-        public PerspexProperty Property
-        {
-            get;
-            set;
-        }
-
-        /// <summary>
-        /// Gets or sets an observable which produces the value for the property.
-        /// </summary>
-        public IObservable<object> Source
-        {
-            get;
-            set;
-        }
-
-        /// <summary>
-        /// Applies the setter to the control.
-        /// </summary>
-        /// <param name="style">The style that is being applied.</param>
-        /// <param name="control">The control.</param>
-        /// <param name="activator">An optional activator.</param>
-        public void Apply(IStyle style, IStyleable control, IObservable<bool> activator)
-        {
-            if (activator == null)
-            {
-                control.Bind(Property, Source, BindingPriority.Style);
-            }
-            else
-            {
-                var binding = new StyleBinding(activator, Source, style.ToString());
-                control.Bind(Property, binding, BindingPriority.StyleTrigger);
-            }
-        }
-    }
-}

src/Perspex.Styling/Styling/Selectors.cs

@@ -240,7 +240,7 @@ namespace Perspex.Styling
 
         private static SelectorMatch MatchPropertyEquals(IStyleable x, PerspexProperty property, object value)
         {
-            if (!x.IsRegistered(property))
+            if (!PerspexPropertyRegistry.Instance.IsRegistered(x, property))
             {
                 return SelectorMatch.False;
             }

src/Perspex.Styling/Styling/Setter.cs

@@ -2,7 +2,10 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
+using System.Reactive.Subjects;
+using Perspex.Data;
 using Perspex.Metadata;
+using Perspex.Reactive;
 
 namespace Perspex.Styling
 {
@@ -46,6 +49,7 @@ namespace Perspex.Styling
         /// Gets or sets the property value.
         /// </summary>
         [Content]
+        [AssignBinding]
         public object Value
         {
             get;
@@ -60,15 +64,67 @@ namespace Perspex.Styling
         /// <param name="activator">An optional activator.</param>
         public void Apply(IStyle style, IStyleable control, IObservable<bool> activator)
         {
-            if (activator == null)
+            Contract.Requires<ArgumentNullException>(control != null);
+
+            var description = style?.ToString();
+
+            if (Property == null)
+            {
+                throw new InvalidOperationException("Setter.Property must be set.");
+            }
+
+            var binding = Value as IBinding;
+
+            if (binding != null)
             {
-                control.SetValue(Property, Value, BindingPriority.Style);
+                if (activator == null)
+                {
+                    Bind(control, Property, binding);
+                }
+                else
+                {
+                    var subject = binding.CreateSubject(control, Property);
+                    var activated = new ActivatedSubject(activator, subject, description);
+                    Bind(control, Property, binding, activated);
+                }
             }
             else
             {
-                var binding = new StyleBinding(activator, Value, style.ToString());
+                if (activator == null)
-                control.Bind(Property, binding, BindingPriority.StyleTrigger);
+                {
+                    control.SetValue(Property, Value, BindingPriority.Style);
+                }
+                else
+                {
+                    var activated = new ActivatedValue(activator, Value, description);
+                    control.Bind(Property, activated, BindingPriority.StyleTrigger);
+                }
+            }
+        }
+
+        private void Bind(IStyleable control, PerspexProperty property, IBinding binding)
+        {
+            Bind(control, property, binding, binding.CreateSubject(control, property));
+        }
+
+        private void Bind(
+            IStyleable control, 
+            PerspexProperty property, 
+            IBinding binding, 
+            ISubject<object> subject)
+        {
+            var mode = binding.Mode;
+
+            if (mode == BindingMode.Default)
+            {
+                mode = property.DefaultBindingMode;
             }
+
+            control.Bind(
+                property,
+                subject,
+                mode,
+                binding.Priority);
         }
     }
 }

src/Perspex.Styling/Styling/StyleBinding.cs

@@ -1,107 +0,0 @@
-// Copyright (c) The Perspex Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System;
-using System.Reactive;
-using System.Reactive.Linq;
-
-namespace Perspex.Styling
-{
-    /// <summary>
-    /// Provides an observable for a style.
-    /// </summary>
-    /// <remarks>
-    /// A <see cref="StyleBinding"/> has two inputs: an activator observable and either an
-    /// <see cref="ActivatedValue"/> or a <see cref="Source"/> observable which produces the
-    /// activated value. When the activator produces true, the <see cref="StyleBinding"/> will
-    /// produce the current activated value. When the activator produces false it will produce
-    /// <see cref="PerspexProperty.UnsetValue"/>.
-    /// </remarks>
-    internal class StyleBinding : ObservableBase<object>, IDescription
-    {
-        /// <summary>
-        /// The activator.
-        /// </summary>
-        private readonly IObservable<bool> _activator;
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="StyleBinding"/> class.
-        /// </summary>
-        /// <param name="activator">The activator.</param>
-        /// <param name="activatedValue">The activated value.</param>
-        /// <param name="description">The binding description.</param>
-        public StyleBinding(
-            IObservable<bool> activator,
-            object activatedValue,
-            string description)
-        {
-            _activator = activator;
-            ActivatedValue = activatedValue;
-            Description = description;
-        }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="StyleBinding"/> class.
-        /// </summary>
-        /// <param name="activator">The activator.</param>
-        /// <param name="source">An observable that produces the activated value.</param>
-        /// <param name="description">The binding description.</param>
-        public StyleBinding(
-            IObservable<bool> activator,
-            IObservable<object> source,
-            string description)
-        {
-            _activator = activator;
-            Description = description;
-            Source = source;
-        }
-
-        /// <summary>
-        /// Gets the activated value.
-        /// </summary>
-        public object ActivatedValue
-        {
-            get;
-        }
-
-        /// <summary>
-        /// Gets a description of the binding.
-        /// </summary>
-        public string Description
-        {
-            get;
-        }
-
-        /// <summary>
-        /// Gets an observable which produces the <see cref="ActivatedValue"/>.
-        /// </summary>
-        public IObservable<object> Source
-        {
-            get;
-        }
-
-        /// <summary>
-        /// Notifies the provider that an observer is to receive notifications.
-        /// </summary>
-        /// <param name="observer">The observer.</param>
-        /// <returns>IDisposable object used to unsubscribe from the observable sequence.</returns>
-        protected override IDisposable SubscribeCore(IObserver<object> observer)
-        {
-            Contract.Requires<ArgumentNullException>(observer != null);
-
-            if (Source == null)
-            {
-                return _activator
-                    .Select(active => active ? ActivatedValue : PerspexProperty.UnsetValue)
-                    .Subscribe(observer);
-            }
-            else
-            {
-                return _activator
-                    .CombineLatest(Source, (x, y) => new { Active = x, Value = y })
-                    .Select(x => x.Active ? x.Value : PerspexProperty.UnsetValue)
-                    .Subscribe(observer);
-            }
-        }
-    }
-}

tests/Perspex.Base.UnitTests/Perspex.Base.UnitTests.csproj

@@ -82,6 +82,7 @@
     <Compile Include="Collections\PerspexListTests.cs" />
     <Compile Include="Collections\PropertyChangedTracker.cs" />
     <Compile Include="PerspexObjectTests_Direct.cs" />
+    <Compile Include="PerspexObjectTests_GetSubject.cs" />
     <Compile Include="PerspexObjectTests_GetObservable.cs" />
     <Compile Include="PerspexPropertyRegistryTests.cs" />
     <Compile Include="PerspexObjectTests_Validation.cs" />

tests/Perspex.Base.UnitTests/PerspexObjectTests_Binding.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
+using Perspex.Data;
 using Xunit;
 
 namespace Perspex.Base.UnitTests
@@ -81,7 +82,7 @@ namespace Perspex.Base.UnitTests
         }
 
         [Fact]
-        public void Two_Way_Binding_Works()
+        public void Two_Way_Separate_Binding_Works()
         {
             Class1 obj1 = new Class1();
             Class1 obj2 = new Class1();
@@ -142,34 +143,6 @@ namespace Perspex.Base.UnitTests
             Assert.Equal("third", obj2.GetValue(Class1.FooProperty));
         }
 
-        [Fact]
-        public void BindTwoWay_Gets_Initial_Value_From_Source()
-        {
-            Class1 source = new Class1();
-            Class1 target = new Class1();
-
-            source.SetValue(Class1.FooProperty, "initial");
-            target.BindTwoWay(Class1.FooProperty, source, Class1.FooProperty);
-
-            Assert.Equal("initial", target.GetValue(Class1.FooProperty));
-        }
-
-        [Fact]
-        public void BindTwoWay_Updates_Values()
-        {
-            Class1 source = new Class1();
-            Class1 target = new Class1();
-
-            source.SetValue(Class1.FooProperty, "first");
-            target.BindTwoWay(Class1.FooProperty, source, Class1.FooProperty);
-
-            Assert.Equal("first", target.GetValue(Class1.FooProperty));
-            source.SetValue(Class1.FooProperty, "second");
-            Assert.Equal("second", target.GetValue(Class1.FooProperty));
-            target.SetValue(Class1.FooProperty, "third");
-            Assert.Equal("third", source.GetValue(Class1.FooProperty));
-        }
-
         [Fact]
         public void Local_Binding_Overwrites_Local_Value()
         {
@@ -234,7 +207,7 @@ namespace Perspex.Base.UnitTests
         {
             Class1 target1 = new Class1();
             Class1 target2 = new Class1();
-            BindingDescriptor binding = Class1.FooProperty.Bind().WithMode(BindingMode.OneWay);
+            IndexerDescriptor binding = Class1.FooProperty.Bind().WithMode(BindingMode.OneWay);
 
             target1.SetValue(Class1.FooProperty, "first");
             target2[binding] = target1[!Class1.FooProperty];
@@ -248,7 +221,7 @@ namespace Perspex.Base.UnitTests
         {
             Class1 target1 = new Class1();
             Class1 target2 = new Class1();
-            BindingDescriptor binding = Class1.FooProperty.Bind().WithMode(BindingMode.TwoWay);
+            IndexerDescriptor binding = Class1.FooProperty.Bind().WithMode(BindingMode.TwoWay);
 
             target1.SetValue(Class1.FooProperty, "first");
             target2[binding] = target1[!Class1.FooProperty];
@@ -264,7 +237,7 @@ namespace Perspex.Base.UnitTests
         {
             Class1 target1 = new Class1();
             Class1 target2 = new Class1();
-            BindingDescriptor binding = Class1.FooProperty.Bind().WithMode(BindingMode.OneTime);
+            IndexerDescriptor binding = Class1.FooProperty.Bind().WithMode(BindingMode.OneTime);
 
             target1.SetValue(Class1.FooProperty, "first");
             target2[binding] = target1[!Class1.FooProperty];

tests/Perspex.Base.UnitTests/PerspexObjectTests_Direct.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Reactive.Subjects;
+using Perspex.Data;
 using Xunit;
 
 namespace Perspex.Base.UnitTests

tests/Perspex.Base.UnitTests/PerspexObjectTests_GetSubject.cs

@@ -0,0 +1,49 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Reactive.Linq;
+using Xunit;
+
+namespace Perspex.Base.UnitTests
+{
+    public class PerspexObjectTests_GetSubject
+    {
+        [Fact]
+        public void GetSubject_Returns_Values()
+        {
+            var source = new Class1 { Foo = "foo" };
+            var target = source.GetSubject(Class1.FooProperty);
+            var result = new List<string>();
+
+            target.Subscribe(x => result.Add(x));
+            source.Foo = "bar";
+            source.Foo = "baz";
+
+            Assert.Equal(new[] { "foo", "bar", "baz" }, result);
+        }
+
+        [Fact]
+        public void GetSubject_Sets_Values()
+        {
+            var source = new Class1 { Foo = "foo" };
+            var target = source.GetSubject(Class1.FooProperty);
+
+            target.OnNext("bar");
+            Assert.Equal("bar", source.Foo);
+        }
+
+        private class Class1 : PerspexObject
+        {
+            public static readonly PerspexProperty<string> FooProperty =
+                PerspexProperty.Register<Class1, string>("Foo", "foodefault");
+
+            public string Foo
+            {
+                get { return GetValue(FooProperty); }
+                set { SetValue(FooProperty, value); }
+            }
+        }
+    }
+}

tests/Perspex.Base.UnitTests/PerspexObjectTests_SetValue.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
+using Perspex.Data;
 using Xunit;
 
 namespace Perspex.Base.UnitTests

tests/Perspex.Base.UnitTests/PerspexPropertyTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
+using Perspex.Data;
 using Xunit;
 
 namespace Perspex.Base.UnitTests

tests/Perspex.Controls.UnitTests/Primitives/SelectingItemsControlTests_Multiple.cs

@@ -9,6 +9,7 @@ using Perspex.Collections;
 using Perspex.Controls.Presenters;
 using Perspex.Controls.Primitives;
 using Perspex.Controls.Templates;
+using Perspex.Data;
 using Perspex.Markup.Xaml.Data;
 using Xunit;
 
@@ -418,8 +419,8 @@ namespace Perspex.Controls.UnitTests.Primitives
             };
 
             // Bind Items and SelectedItems to the VM.
-            itemsBinding.Bind(target, TestSelector.ItemsProperty);
+            target.Bind(TestSelector.ItemsProperty, itemsBinding);
-            selectedItemsBinding.Bind(target, TestSelector.SelectedItemsProperty);
+            target.Bind(TestSelector.SelectedItemsProperty, selectedItemsBinding);
 
             // Set DataContext and SelectedIndex
             target.DataContext = vm;
@@ -451,7 +452,7 @@ namespace Perspex.Controls.UnitTests.Primitives
             };
 
             var itemsBinding = new Binding { Path = "Items" };
-            itemsBinding.Bind(target, TestSelector.ItemsProperty);
+            target.Bind(TestSelector.ItemsProperty, itemsBinding);
 
             Assert.Same(data.Items, target.Items);
 

tests/Perspex.LeakTests/ControlTests.cs

@@ -194,7 +194,8 @@ namespace Perspex.LeakTests
                     Path = "Name"
                 };
 
-                binding.Bind((TextBox)window.Content, TextBox.TextProperty);
+                var textBox = (TextBox)window.Content;
+                textBox.Bind(TextBox.TextProperty, binding);
 
                 // Do a layout and make sure that TextBox gets added to visual tree and its 
                 // Text property set.
@@ -272,8 +273,7 @@ namespace Perspex.LeakTests
                         {
                             new FuncTreeDataTemplate<Node>(
                                 x => new TextBlock { Text = x.Name },
-                                x => x.Children,
+                                x => x.Children)
-                                x => true)
                         },
                         Items = nodes
                     }

tests/Perspex.Markup.Xaml.UnitTests/Data/BindingTests.cs

@@ -1,14 +1,12 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
-using System;
-using System.Globalization;
-using System.Reactive.Linq;
-using System.Reactive.Subjects;
 using Moq;
 using Perspex.Controls;
+using Perspex.Data;
 using Perspex.Markup.Data;
 using Perspex.Markup.Xaml.Data;
+using ReactiveUI;
 using Xunit;
 
 namespace Perspex.Markup.Xaml.UnitTests.Data
@@ -18,101 +16,101 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
         [Fact]
         public void OneWay_Binding_Should_Be_Set_Up()
         {
-            var target = CreateTarget();
+            var source = new Source { Foo = "foo" };
+            var target = new TextBlock { DataContext = source };
             var binding = new Binding
             {
                 Path = "Foo",
                 Mode = BindingMode.OneWay,
             };
 
-            binding.Bind(target.Object, TextBox.TextProperty);
+            target.Bind(TextBox.TextProperty, binding);
 
-            target.Verify(x => x.Bind(
+            Assert.Equal("foo", target.Text);
-                TextBox.TextProperty, 
+            source.Foo = "bar";
-                It.IsAny<IObservable<object>>(), 
+            Assert.Equal("bar", target.Text);
-                BindingPriority.LocalValue));
+            target.Text = "baz";
+            Assert.Equal("bar", source.Foo);
         }
 
         [Fact]
         public void TwoWay_Binding_Should_Be_Set_Up()
         {
-            var target = CreateTarget();
+            var source = new Source { Foo = "foo" };
+            var target = new TextBlock { DataContext = source };
             var binding = new Binding
             {
                 Path = "Foo",
                 Mode = BindingMode.TwoWay,
             };
 
-            binding.Bind(target.Object, TextBox.TextProperty);
+            target.Bind(TextBox.TextProperty, binding);
 
-            target.Verify(x => x.BindTwoWay(
+            Assert.Equal("foo", target.Text);
-                TextBox.TextProperty,
+            source.Foo = "bar";
-                It.IsAny<ISubject<object>>(),
+            Assert.Equal("bar", target.Text);
-                BindingPriority.LocalValue));
+            target.Text = "baz";
+            Assert.Equal("baz", source.Foo);
         }
 
         [Fact]
         public void OneTime_Binding_Should_Be_Set_Up()
         {
-            var dataContext = new BehaviorSubject<object>(null);
+            var source = new Source { Foo = "foo" };
-            var expression = new BehaviorSubject<object>(null);
+            var target = new TextBlock { DataContext = source };
-            var target = CreateTarget(dataContext: dataContext);
             var binding = new Binding
             {
                 Path = "Foo",
                 Mode = BindingMode.OneTime,
             };
 
-            binding.Bind(target.Object, TextBox.TextProperty, expression);
+            target.Bind(TextBox.TextProperty, binding);
 
-            target.Verify(x => x.SetValue(
+            Assert.Equal("foo", target.Text);
-                (PerspexProperty)TextBox.TextProperty, 
+            source.Foo = "bar";
-                null, 
+            Assert.Equal("foo", target.Text);
-                BindingPriority.LocalValue));
+            target.Text = "baz";
-            target.ResetCalls();
+            Assert.Equal("bar", source.Foo);
-
-            expression.OnNext("foo");
-            dataContext.OnNext(1);
-
-            target.Verify(x => x.SetValue(
-                (PerspexProperty)TextBox.TextProperty,
-                "foo",
-                BindingPriority.LocalValue));
         }
 
         [Fact]
         public void OneWayToSource_Binding_Should_Be_Set_Up()
         {
-            var textObservable = new Mock<IObservable<string>>();
+            var source = new Source { Foo = "foo" };
-            var expression = new Mock<ISubject<object>>();
+            var target = new TextBlock { DataContext = source, Text = "bar" };
-            var target = CreateTarget(text: textObservable.Object);
             var binding = new Binding
             {
                 Path = "Foo",
                 Mode = BindingMode.OneWayToSource,
             };
 
-            binding.Bind(target.Object, TextBox.TextProperty, expression.Object);
+            target.Bind(TextBox.TextProperty, binding);
 
-            textObservable.Verify(x => x.Subscribe(expression.Object));
+            Assert.Equal("bar", source.Foo);
+            target.Text = "baz";
+            Assert.Equal("baz", source.Foo);
+            source.Foo = "quz";
+            Assert.Equal("baz", target.Text);
         }
 
         [Fact]
         public void Default_BindingMode_Should_Be_Used()
         {
-            var target = CreateTarget(null);
+            // Default for TextBox.Text is two-way.
+            var source = new Source { Foo = "foo" };
+            var target = new TextBlock { DataContext = source };
             var binding = new Binding
             {
                 Path = "Foo",
             };
 
-            binding.Bind(target.Object, TextBox.TextProperty);
+            target.Bind(TextBox.TextProperty, binding);
 
-            // Default for TextBox.Text is two-way.
+            Assert.Equal("foo", target.Text);
-            target.Verify(x => x.BindTwoWay(
+            source.Foo = "bar";
-                TextBox.TextProperty,
+            Assert.Equal("bar", target.Text);
-                It.IsAny<ISubject<object>>(),
+            target.Text = "baz";
-                BindingPriority.LocalValue));
+            Assert.Equal("baz", source.Foo);
         }
 
         [Fact]
@@ -131,7 +129,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Header",
             };
 
-            binding.Bind(parent.Child, Control.DataContextProperty);
+            parent.Child.Bind(Control.DataContextProperty, binding);
 
             Assert.Equal("Foo", parent.Child.DataContext);
 
@@ -155,7 +153,8 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Foo",
             };
 
-            binding.Bind(child, Control.DataContextProperty);
+            child.Bind(Control.DataContextProperty, binding);
+
             Assert.Null(child.DataContext);
             parent.Child = child;
             Assert.Equal("foo", child.DataContext);
@@ -164,13 +163,13 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
         [Fact]
         public void Should_Use_DefaultValueConverter_When_No_Converter_Specified()
         {
-            var target = CreateTarget(null);
+            var target = new TextBlock(); ;
             var binding = new Binding
             {
                 Path = "Foo",
             };
 
-            var result = binding.CreateSubject(target.Object, TextBox.TextProperty.PropertyType);
+            var result = binding.CreateSubject(target, TextBox.TextProperty);
 
             Assert.IsType<DefaultValueConverter>(((ExpressionSubject)result).Converter);
         }
@@ -178,7 +177,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
         [Fact]
         public void Should_Use_Supplied_Converter()
         {
-            var target = CreateTarget(null);
+            var target = new TextBlock();
             var converter = new Mock<IValueConverter>();
             var binding = new Binding
             {
@@ -186,7 +185,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Foo",
             };
 
-            var result = binding.CreateSubject(target.Object, TextBox.TextProperty.PropertyType);
+            var result = binding.CreateSubject(target, TextBox.TextProperty);
 
             Assert.Same(converter.Object, ((ExpressionSubject)result).Converter);
         }
@@ -194,7 +193,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
         [Fact]
         public void Should_Pass_ConverterParameter_To_Supplied_Converter()
         {
-            var target = CreateTarget();
+            var target = new TextBlock();
             var converter = new Mock<IValueConverter>();
             var binding = new Binding
             {
@@ -203,7 +202,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Bar",
             };
 
-            var result = binding.CreateSubject(target.Object, TextBox.TextProperty.PropertyType);
+            var result = binding.CreateSubject(target, TextBox.TextProperty);
 
             Assert.Same("foo", ((ExpressionSubject)result).ConverterParameter);
         }
@@ -239,8 +238,8 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
             };
 
             // Bind Foo and Bar to the VM.
-            fooBinding.Bind(target, OldDataContextTest.FooProperty);
+            target.Bind(OldDataContextTest.FooProperty, fooBinding);
-            barBinding.Bind(target, OldDataContextTest.BarProperty);
+            target.Bind(OldDataContextTest.BarProperty, barBinding);
             target.DataContext = vm;
 
             // Make sure the control's Foo and Bar properties are read from the VM
@@ -261,24 +260,15 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
             Assert.Equal(2, vm.Bar);
         }
 
-        private Mock<IObservablePropertyBag> CreateTarget(object dataContext)
+        public class Source : ReactiveObject
         {
-            return CreateTarget(dataContext: Observable.Never<object>().StartWith(dataContext));
+            private string _foo;
-        }
 
-        private Mock<IObservablePropertyBag> CreateTarget(
+            public string Foo
-            IObservable<object> dataContext = null,
+            {
-            IObservable<string> text = null)
+                get { return _foo; }
-        {
+                set { this.RaiseAndSetIfChanged(ref _foo, value); }
-            var result = new Mock<IObservablePropertyBag>();
+            }
-
-            dataContext = dataContext ?? Observable.Never<object>().StartWith((object)null);
-            text = text ?? Observable.Never<string>().StartWith((string)null);
-
-            result.Setup(x => x.GetObservable(Control.DataContextProperty)).Returns(dataContext);
-            result.Setup(x => x.GetObservable((PerspexProperty)Control.DataContextProperty)).Returns(dataContext);
-            result.Setup(x => x.GetObservable((PerspexProperty)TextBox.TextProperty)).Returns(text);
-            return result;
         }
 
         private class OldDataContextViewModel
@@ -297,7 +287,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
 
             public OldDataContextTest()
             {
-                Bind(BarProperty, GetObservable(FooProperty));
+                Bind(BarProperty, this.GetObservable(FooProperty));
             }
         }
     }

tests/Perspex.Markup.Xaml.UnitTests/Data/BindingTests_ElementName.cs

@@ -38,7 +38,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Text",
             };
 
-            binding.Bind(target, TextBlock.TextProperty);
+            target.Bind(TextBox.TextProperty, binding);
 
             Assert.Equal("foo", target.Text);
         }
@@ -73,7 +73,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 ElementName = "source",
             };
 
-            binding.Bind(target, ContentControl.ContentProperty);
+            target.Bind(ContentControl.ContentProperty, binding);
 
             Assert.Same(source, target.Content);
         }
@@ -104,7 +104,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Text",
             };
 
-            binding.Bind(target, TextBlock.TextProperty);
+            target.Bind(TextBox.TextProperty, binding);
 
             stackPanel.Children.Add(new TextBlock
             {
@@ -140,7 +140,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 ElementName = "source",
             };
 
-            binding.Bind(target, ContentControl.ContentProperty);
+            target.Bind(ContentControl.ContentProperty, binding);
 
             var source = new TextBlock
             {

tests/Perspex.Markup.Xaml.UnitTests/Data/BindingTests_TemplatedParent.cs

@@ -6,6 +6,7 @@ using System.Reactive.Linq;
 using System.Reactive.Subjects;
 using Moq;
 using Perspex.Controls;
+using Perspex.Data;
 using Perspex.Markup.Xaml.Data;
 using Perspex.Styling;
 using Xunit;
@@ -26,7 +27,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Foo",
             };
 
-            binding.Bind(target.Object, TextBox.TextProperty);
+            target.Object.Bind(TextBox.TextProperty, binding);
 
             target.Verify(x => x.Bind(
                 TextBox.TextProperty, 
@@ -46,48 +47,28 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 Path = "Foo",
             };
 
-            binding.Bind(target.Object, TextBox.TextProperty);
+            target.Object.Bind(TextBox.TextProperty, binding);
 
-            target.Verify(x => x.BindTwoWay(
+            target.Verify(x => x.Bind(
                 TextBox.TextProperty,
                 It.IsAny<ISubject<object>>(),
                 BindingPriority.TemplatedParent));
         }
 
-        [Fact]
+        private Mock<IPerspexObject> CreateTarget(ITemplatedControl templatedParent)
-        public void OneWayToSource_Binding_Should_Be_Set_Up()
-        {
-            var textObservable = new Mock<IObservable<string>>();
-            var expression = new Mock<ISubject<object>>();
-            var target = CreateTarget(text: textObservable.Object);
-            var binding = new Binding
-            {
-                Path = "Foo",
-                Mode = BindingMode.OneWayToSource,
-            };
-
-            binding.Bind(target.Object, TextBox.TextProperty, expression.Object);
-
-            textObservable.Verify(x => x.Subscribe(expression.Object));
-        }
-
-        private Mock<IObservablePropertyBag> CreateTarget(ITemplatedControl templatedParent)
         {
-            return CreateTarget(templatedParent: Observable.Never<ITemplatedControl>().StartWith(templatedParent));
+            return CreateTarget(templatedParent: templatedParent);
         }
 
-        private Mock<IObservablePropertyBag> CreateTarget(
+        private Mock<IControl> CreateTarget(
-            IObservable<ITemplatedControl> templatedParent = null,
+            ITemplatedControl templatedParent = null,
-            IObservable<string> text = null)
+            string text = null)
         {
-            var result = new Mock<IObservablePropertyBag>();
+            var result = new Mock<IControl>();
-
-            templatedParent = templatedParent ?? Observable.Never<ITemplatedControl>().StartWith((ITemplatedControl)null);
-            text = text ?? Observable.Never<string>().StartWith((string)null);
 
-            result.Setup(x => x.GetObservable(Control.TemplatedParentProperty)).Returns(templatedParent);
+            result.Setup(x => x.GetValue(Control.TemplatedParentProperty)).Returns(templatedParent);
-            result.Setup(x => x.GetObservable((PerspexProperty)Control.TemplatedParentProperty)).Returns(templatedParent);
+            result.Setup(x => x.GetValue((PerspexProperty)Control.TemplatedParentProperty)).Returns(templatedParent);
-            result.Setup(x => x.GetObservable((PerspexProperty)TextBox.TextProperty)).Returns(text);
+            result.Setup(x => x.GetValue((PerspexProperty)TextBox.TextProperty)).Returns(text);
             return result;
         }
     }

tests/Perspex.Markup.Xaml.UnitTests/Data/MultiBindingTests.cs

@@ -6,7 +6,6 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
 using System.Reactive.Linq;
-using System.Reactive.Subjects;
 using Moq;
 using Perspex.Controls;
 using Perspex.Markup.Xaml.Data;
@@ -31,12 +30,10 @@ namespace Perspex.Markup.Xaml.UnitTests.Data
                 }
             };
 
-            var target = new Mock<IObservablePropertyBag>();
+            var target = new Mock<IPerspexObject>();
             target.Setup(x => x.GetValue(Control.DataContextProperty)).Returns(source);
-            target.Setup(x => x.GetObservable(Control.DataContextProperty)).Returns(
-                Observable.Never<object>().StartWith(source));
 
-            var subject = binding.CreateSubject(target.Object, typeof(string));
+            var subject = binding.CreateSubject(target.Object, null);
             var result = await subject.Take(1);
 
             Assert.Equal("1,2,3", result);

tests/Perspex.Markup.Xaml.UnitTests/Perspex.Markup.Xaml.UnitTests.csproj

@@ -43,9 +43,6 @@
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
   <ItemGroup>
-    <Reference Include="Octokit">
-      <HintPath>..\..\packages\Octokit.0.14.0\lib\net45\Octokit.dll</HintPath>
-    </Reference>
     <Reference Include="Splat, Version=1.6.2.0, Culture=neutral, processorArchitecture=MSIL">
       <HintPath>..\..\packages\Splat.1.6.2\lib\Net45\Splat.dll</HintPath>
       <Private>True</Private>
@@ -104,7 +101,9 @@
     <Compile Include="SampleModel\Repository.cs" />
     <Compile Include="SampleModel\UserRepositoriesViewModel.cs" />
     <Compile Include="SamplePerspexObject.cs" />
+    <Compile Include="StyleTests.cs" />
     <Compile Include="Templates\DataTemplateTests.cs" />
+    <Compile Include="Templates\TreeDataTemplateTests.cs" />
     <Compile Include="TestRoot.cs" />
     <Compile Include="TypeProviderMock.cs" />
     <Compile Include="ViewModelMock.cs" />

tests/Perspex.Markup.Xaml.UnitTests/StyleTests.cs

@@ -0,0 +1,120 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System.Linq;
+using System.Reactive.Linq;
+using Moq;
+using Perspex.Controls;
+using Perspex.Controls.Primitives;
+using Perspex.Data;
+using Perspex.Markup.Xaml.Data;
+using Perspex.Platform;
+using Perspex.Styling;
+using Xunit;
+
+namespace Perspex.Markup.Xaml.UnitTests
+{
+    public class StyleTests
+    {
+        [Fact]
+        public void Binding_Should_Be_Assigned_To_Setter_Value_Instead_Of_Bound()
+        {
+            using (PerspexLocator.EnterScope())
+            {
+                PerspexLocator.CurrentMutable
+                    .Bind<IPclPlatformWrapper>()
+                    .ToConstant(Mock.Of<IPclPlatformWrapper>());
+
+                var xaml = "<Style xmlns='https://github.com/perspex'><Setter Value='{Binding}'/></Style>";
+                var loader = new PerspexXamlLoader();
+                var style = (Style)loader.Load(xaml);
+                var setter = (Setter)(style.Setters.First());
+
+                Assert.IsType<Binding>(setter.Value);
+            }                
+        }
+
+        [Fact]
+        public void Setter_With_TwoWay_Binding_Should_Update_Source()
+        {
+            using (PerspexLocator.EnterScope())
+            {
+                PerspexLocator.CurrentMutable
+                    .Bind<IPlatformThreadingInterface>()
+                    .ToConstant(Mock.Of<IPlatformThreadingInterface>(x => 
+                        x.CurrentThreadIsLoopThread == true));
+
+                var data = new Data
+                {
+                    Foo = "foo",
+                };
+
+                var control = new TextBox
+                {
+                    DataContext = data,
+                };
+
+                var setter = new Setter
+                {
+                    Property = TextBox.TextProperty,
+                    Value = new Binding
+                    {
+                        Path = "Foo",
+                        Mode = BindingMode.TwoWay
+                    }
+                };
+
+                setter.Apply(null, control, null);
+                Assert.Equal("foo", control.Text);
+
+                control.Text = "bar";
+                Assert.Equal("bar", data.Foo);
+            }
+        }
+
+        [Fact]
+        public void Setter_With_TwoWay_Binding_And_Activator_Should_Update_Source()
+        {
+            using (PerspexLocator.EnterScope())
+            {
+                PerspexLocator.CurrentMutable
+                    .Bind<IPlatformThreadingInterface>()
+                    .ToConstant(Mock.Of<IPlatformThreadingInterface>(x =>
+                        x.CurrentThreadIsLoopThread == true));
+
+                var data = new Data
+                {
+                    Foo = "foo",
+                };
+
+                var control = new TextBox
+                {
+                    DataContext = data,
+                };
+
+                var setter = new Setter
+                {
+                    Property = TextBox.TextProperty,
+                    Value = new Binding
+                    {
+                        Path = "Foo",
+                        Mode = BindingMode.TwoWay
+                    }
+                };
+
+                var activator = Observable.Never<bool>().StartWith(true);
+
+                setter.Apply(null, control, activator);
+                Assert.Equal("foo", control.Text);
+
+                control.Text = "bar";
+                Assert.Equal("bar", data.Foo);
+            }
+        }
+
+        private class Data
+        {
+            public string Foo { get; set; }
+        }
+    }
+}

tests/Perspex.Markup.Xaml.UnitTests/Templates/TreeDataTemplateTests.cs

@@ -0,0 +1,34 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System.Linq;
+using Moq;
+using Perspex.Controls.Templates;
+using Perspex.Markup.Xaml.Data;
+using Perspex.Markup.Xaml.Templates;
+using Perspex.Platform;
+using Xunit;
+
+namespace Perspex.Markup.Xaml.UnitTests
+{
+    public class TreeDataTemplateTests
+    {
+        [Fact]
+        public void Binding_Should_Be_Assigned_To_ItemsSource_Instead_Of_Bound()
+        {
+            using (PerspexLocator.EnterScope())
+            {
+                PerspexLocator.CurrentMutable
+                    .Bind<IPclPlatformWrapper>()
+                    .ToConstant(Mock.Of<IPclPlatformWrapper>());
+
+                var xaml = "<DataTemplates xmlns='https://github.com/perspex'><TreeDataTemplate ItemsSource='{Binding}'/></DataTemplates>";
+                var loader = new PerspexXamlLoader();
+                var templates = (DataTemplates)loader.Load(xaml);
+                var template = (TreeDataTemplate)(templates.First());
+
+                Assert.IsType<Binding>(template.ItemsSource);
+            }                
+        }
+    }
+}

tests/Perspex.Styling.UnitTests/ActivatedObservableTests.cs

@@ -0,0 +1,70 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
+using Xunit;
+
+namespace Perspex.Styling.UnitTests
+{
+    public class ActivatedObservableTests
+    {
+        [Fact]
+        public void Should_Produce_Correct_Values()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var source = new BehaviorSubject<object>(1);
+            var target = new ActivatedObservable(activator, source, string.Empty);
+            var result = new List<object>();
+
+            target.Subscribe(x => result.Add(x));
+
+            activator.OnNext(true);
+            source.OnNext(2);
+            activator.OnNext(false);
+            source.OnNext(3);
+            activator.OnNext(true);
+
+            Assert.Equal(
+                new[] 
+                {
+                    PerspexProperty.UnsetValue,
+                    1,
+                    2,
+                    PerspexProperty.UnsetValue,
+                    3,
+                }, 
+                result);
+        }
+
+        [Fact]
+        public void Should_Complete_When_Source_Completes()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var source = new BehaviorSubject<object>(1);
+            var target = new ActivatedObservable(activator, source, string.Empty);
+            var completed = false;
+
+            target.Subscribe(_ => { }, () => completed = true);
+            source.OnCompleted();
+
+            Assert.True(completed);
+        }
+
+        [Fact]
+        public void Should_Complete_When_Activator_Completes()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var source = new BehaviorSubject<object>(1);
+            var target = new ActivatedObservable(activator, source, string.Empty);
+            var completed = false;
+
+            target.Subscribe(_ => { }, () => completed = true);
+            activator.OnCompleted();
+
+            Assert.True(completed);
+        }
+    }
+}

tests/Perspex.Styling.UnitTests/ActivatedSubjectTests.cs

@@ -0,0 +1,98 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Reactive.Disposables;
+using System.Reactive.Subjects;
+using Xunit;
+
+namespace Perspex.Styling.UnitTests
+{
+    public class ActivatedSubjectTests
+    {
+        [Fact]
+        public void Should_Set_Values()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var source = new TestSubject();
+            var target = new ActivatedSubject(activator, source, string.Empty);
+
+            target.OnNext("bar");
+            Assert.Equal(PerspexProperty.UnsetValue, source.Value);
+            activator.OnNext(true);
+            target.OnNext("baz");
+            Assert.Equal("baz", source.Value);
+            activator.OnNext(false);
+            Assert.Equal(PerspexProperty.UnsetValue, source.Value);
+            target.OnNext("bax");
+            activator.OnNext(true);
+            Assert.Equal("bax", source.Value);
+        }
+
+        [Fact]
+        public void Should_Invoke_OnCompleted_On_Activator_Completed()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var source = new TestSubject();
+            var target = new ActivatedSubject(activator, source, string.Empty);
+
+            activator.OnCompleted();
+
+            Assert.True(source.Completed);
+        }
+
+        [Fact]
+        public void Should_Invoke_OnError_On_Activator_Error()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var source = new TestSubject();
+            var target = new ActivatedSubject(activator, source, string.Empty);
+
+            activator.OnError(new Exception());
+
+            Assert.NotNull(source.Error);
+        }
+
+        private class Class1 : PerspexObject
+        {
+            public static readonly PerspexProperty<string> FooProperty =
+                PerspexProperty.Register<Class1, string>("Foo", "foodefault");
+
+            public string Foo
+            {
+                get { return GetValue(FooProperty); }
+                set { SetValue(FooProperty, value); }
+            }
+        }
+
+        private class TestSubject : ISubject<object>
+        {
+            private IObserver<object> _observer;
+
+            public bool Completed { get; set; }
+            public Exception Error { get; set; }
+            public object Value { get; set; } = PerspexProperty.UnsetValue;
+
+            public void OnCompleted()
+            {
+                Completed = true;
+            }
+
+            public void OnError(Exception error)
+            {
+                Error = error;
+            }
+
+            public void OnNext(object value)
+            {
+                Value = value;
+            }
+
+            public IDisposable Subscribe(IObserver<object> observer)
+            {
+                _observer = observer;
+                return Disposable.Empty;
+            }
+        }
+    }
+}

tests/Perspex.Styling.UnitTests/ActivatedValueTests.cs

@@ -0,0 +1,42 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
+using Xunit;
+
+namespace Perspex.Styling.UnitTests
+{
+    public class ActivatedValueTests
+    {
+        [Fact]
+        public void Should_Produce_Correct_Values()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var target = new ActivatedValue(activator, 1, string.Empty);
+            var result = new List<object>();
+
+            target.Subscribe(x => result.Add(x));
+
+            activator.OnNext(true);
+            activator.OnNext(false);
+
+            Assert.Equal(new[] { PerspexProperty.UnsetValue, 1, PerspexProperty.UnsetValue }, result);
+        }
+
+        [Fact]
+        public void Should_Complete_When_Activator_Completes()
+        {
+            var activator = new BehaviorSubject<bool>(false);
+            var target = new ActivatedValue(activator, 1, string.Empty);
+            var completed = false;
+
+            target.Subscribe(_ => { }, () => completed = true);
+            activator.OnCompleted();
+
+            Assert.True(completed);
+        }
+    }
+}

tests/Perspex.Styling.UnitTests/Perspex.Styling.UnitTests.csproj

@@ -80,6 +80,8 @@
     <Otherwise />
   </Choose>
   <ItemGroup>
+    <Compile Include="ActivatedValueTests.cs" />
+    <Compile Include="ActivatedSubjectTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="SelectorTests_Class.cs" />
     <Compile Include="SelectorTests_Child.cs" />
@@ -90,7 +92,8 @@
     <Compile Include="SelectorTests_OfType.cs" />
     <Compile Include="SelectorTests_Template.cs" />
     <Compile Include="StyleActivatorTests.cs" />
-    <Compile Include="StyleBindingTests.cs" />
+    <Compile Include="ActivatedObservableTests.cs" />
+    <Compile Include="SetterTests.cs" />
     <Compile Include="StyleTests.cs" />
     <Compile Include="TestControlBase.cs" />
     <Compile Include="TestObservable.cs" />

tests/Perspex.Styling.UnitTests/SelectorTests_Child.cs

@@ -6,11 +6,9 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Reactive;
 using System.Reactive.Linq;
-using System.Reactive.Subjects;
-using System.Threading.Tasks;
 using Perspex.Collections;
 using Perspex.Controls;
-using Perspex.Styling;
+using Perspex.Data;
 using Xunit;
 
 namespace Perspex.Styling.UnitTests
@@ -80,6 +78,8 @@ namespace Perspex.Styling.UnitTests
                 Classes = new Classes();
             }
 
+            public event EventHandler<PerspexPropertyChangedEventArgs> PropertyChanged;
+
             public Classes Classes { get; }
 
             public string Name { get; set; }
@@ -96,42 +96,29 @@ namespace Perspex.Styling.UnitTests
 
             IObservable<Unit> IStyleable.StyleDetach { get; }
 
-            public IPropertyBag InheritanceParent
-            {
-                get
-                {
-                    throw new NotImplementedException();
-                }
-            }
-
             IPerspexReadOnlyList<string> IStyleable.Classes => Classes;
 
-            public IDisposable Bind(PerspexProperty property, IObservable<object> source, BindingPriority priority)
+            public object GetValue(PerspexProperty property)
-            {
-                throw new NotImplementedException();
-            }
-
-            public void SetValue(PerspexProperty property, object value, BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
 
-            public IObservable<object> GetObservable(PerspexProperty property)
+            public T GetValue<T>(PerspexProperty<T> property)
             {
                 throw new NotImplementedException();
             }
 
-            public bool IsRegistered(PerspexProperty property)
+            public void SetValue(PerspexProperty property, object value, BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
 
-            public void ClearValue(PerspexProperty property)
+            public void SetValue<T>(PerspexProperty<T> property, T value, BindingPriority priority = BindingPriority.LocalValue)
             {
                 throw new NotImplementedException();
             }
 
-            public object GetValue(PerspexProperty property)
+            public IDisposable Bind(PerspexProperty property, IObservable<object> source, BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
@@ -145,31 +132,6 @@ namespace Perspex.Styling.UnitTests
             {
                 throw new NotImplementedException();
             }
-
-            public IObservable<T> GetObservable<T>(PerspexProperty<T> property)
-            {
-                throw new NotImplementedException();
-            }
-
-            public T GetValue<T>(PerspexProperty<T> property)
-            {
-                throw new NotImplementedException();
-            }
-
-            public void SetValue<T>(PerspexProperty<T> property, T value, BindingPriority priority = BindingPriority.LocalValue)
-            {
-                throw new NotImplementedException();
-            }
-
-            public IDisposable BindTwoWay(PerspexProperty property, PerspexObject source, PerspexProperty sourceProperty, BindingPriority priority = BindingPriority.LocalValue)
-            {
-                throw new NotImplementedException();
-            }
-
-            public IDisposable BindTwoWay(PerspexProperty property, ISubject<object> source, BindingPriority priority = BindingPriority.LocalValue)
-            {
-                throw new NotImplementedException();
-            }
         }
 
         public class TestLogical1 : TestLogical

tests/Perspex.Styling.UnitTests/SelectorTests_Descendent.cs

@@ -5,11 +5,10 @@ using System;
 using System.Linq;
 using System.Reactive;
 using System.Reactive.Linq;
-using System.Reactive.Subjects;
 using System.Threading.Tasks;
 using Perspex.Collections;
 using Perspex.Controls;
-using Perspex.Styling;
+using Perspex.Data;
 using Xunit;
 
 namespace Perspex.Styling.UnitTests
@@ -110,6 +109,8 @@ namespace Perspex.Styling.UnitTests
                 Classes = new Classes();
             }
 
+            public event EventHandler<PerspexPropertyChangedEventArgs> PropertyChanged;
+
             public Classes Classes { get; }
 
             public string Name { get; set; }
@@ -124,44 +125,31 @@ namespace Perspex.Styling.UnitTests
 
             public ITemplatedControl TemplatedParent { get; }
 
-            public IPropertyBag InheritanceParent
-            {
-                get
-                {
-                    throw new NotImplementedException();
-                }
-            }
-
             IPerspexReadOnlyList<string> IStyleable.Classes => Classes;
 
             IObservable<Unit> IStyleable.StyleDetach { get; }
 
-            public IDisposable Bind(PerspexProperty property, IObservable<object> source, BindingPriority priority)
+            public object GetValue(PerspexProperty property)
-            {
-                throw new NotImplementedException();
-            }
-
-            public void SetValue(PerspexProperty property, object value, BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
 
-            public IObservable<object> GetObservable(PerspexProperty property)
+            public T GetValue<T>(PerspexProperty<T> property)
             {
                 throw new NotImplementedException();
             }
 
-            public bool IsRegistered(PerspexProperty property)
+            public void SetValue(PerspexProperty property, object value, BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
 
-            public void ClearValue(PerspexProperty property)
+            public void SetValue<T>(PerspexProperty<T> property, T value, BindingPriority priority = BindingPriority.LocalValue)
             {
                 throw new NotImplementedException();
             }
 
-            public object GetValue(PerspexProperty property)
+            public IDisposable Bind(PerspexProperty property, IObservable<object> source, BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
@@ -175,31 +163,6 @@ namespace Perspex.Styling.UnitTests
             {
                 throw new NotImplementedException();
             }
-
-            public IObservable<T> GetObservable<T>(PerspexProperty<T> property)
-            {
-                throw new NotImplementedException();
-            }
-
-            public T GetValue<T>(PerspexProperty<T> property)
-            {
-                throw new NotImplementedException();
-            }
-
-            public void SetValue<T>(PerspexProperty<T> property, T value, BindingPriority priority = BindingPriority.LocalValue)
-            {
-                throw new NotImplementedException();
-            }
-
-            public IDisposable BindTwoWay(PerspexProperty property, PerspexObject source, PerspexProperty sourceProperty, BindingPriority priority = BindingPriority.LocalValue)
-            {
-                throw new NotImplementedException();
-            }
-
-            public IDisposable BindTwoWay(PerspexProperty property, ISubject<object> source, BindingPriority priority = BindingPriority.LocalValue)
-            {
-                throw new NotImplementedException();
-            }
         }
 
         public class TestLogical1 : TestLogical

tests/Perspex.Styling.UnitTests/SetterTests.cs

@@ -0,0 +1,28 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System.Reactive.Subjects;
+using Moq;
+using Perspex.Controls;
+using Perspex.Data;
+using Xunit;
+
+namespace Perspex.Styling.UnitTests
+{
+    public class SetterTests
+    {
+        [Fact]
+        public void Setter_Should_Apply_Binding_To_Property()
+        {
+            var control = new TextBlock();
+            var subject = new BehaviorSubject<object>("foo");
+            var binding = Mock.Of<IBinding>(x => x.CreateSubject(control, TextBlock.TextProperty) == subject);
+            var style = Mock.Of<IStyle>();
+            var setter = new Setter(TextBlock.TextProperty, binding);
+
+            setter.Apply(style, control, null);
+
+            Assert.Equal("foo", control.Text);
+        }
+    }
+}

tests/Perspex.Styling.UnitTests/StyleBindingTests.cs

@@ -1,79 +0,0 @@
-// Copyright (c) The Perspex Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System;
-using System.Collections.Generic;
-using System.Reactive.Linq;
-using System.Reactive.Subjects;
-using Xunit;
-
-namespace Perspex.Styling.UnitTests
-{
-    public class StyleBindingTests
-    {
-        [Fact]
-        public async void Should_Produce_UnsetValue_On_Activator_False()
-        {
-            var activator = new BehaviorSubject<bool>(false);
-            var target = new StyleBinding(activator, 1, string.Empty);
-            var result = await target.Take(1);
-
-            Assert.Equal(PerspexProperty.UnsetValue, result);
-        }
-
-        [Fact]
-        public async void Should_Produce_Value_On_Activator_True()
-        {
-            var activator = new BehaviorSubject<bool>(true);
-            var target = new StyleBinding(activator, 1, string.Empty);
-            var result = await target.Take(1);
-
-            Assert.Equal(1, result);
-        }
-
-        [Fact]
-        public void Should_Change_Value_On_Activator_Change()
-        {
-            var activator = new BehaviorSubject<bool>(false);
-            var target = new StyleBinding(activator, 1, string.Empty);
-            var result = new List<object>();
-
-            target.Subscribe(x => result.Add(x));
-
-            activator.OnNext(true);
-            activator.OnNext(false);
-
-            Assert.Equal(new[] { PerspexProperty.UnsetValue, 1, PerspexProperty.UnsetValue }, result);
-        }
-
-        [Fact]
-        public void Should_Change_Value_With_Source_Observable()
-        {
-            var activator = new BehaviorSubject<bool>(false);
-            var source = new BehaviorSubject<object>(1);
-            var target = new StyleBinding(activator, source, string.Empty);
-            var result = new List<object>();
-
-            target.Subscribe(x => result.Add(x));
-
-            activator.OnNext(true);
-            source.OnNext(2);
-            activator.OnNext(false);
-
-            Assert.Equal(new[] { PerspexProperty.UnsetValue, 1, 2, PerspexProperty.UnsetValue }, result);
-        }
-
-        [Fact]
-        public void Should_Complete_When_Activator_Completes()
-        {
-            var activator = new BehaviorSubject<bool>(false);
-            var target = new StyleBinding(activator, 1, string.Empty);
-            var completed = false;
-
-            target.Subscribe(_ => { }, () => completed = true);
-            activator.OnCompleted();
-
-            Assert.True(completed);
-        }
-    }
-}