Initial implementation of ExpressionObserver.

11 years ago · 005cd231cc
16 changed files with 858 additions and 0 deletions
--- a/Perspex.sln
+++ b/Perspex.sln
@ -96,6 +96,10 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Perspex.HtmlRenderer", "src
 EndProject
 Project("{D954291E-2A0B-460D-934E-DC6B0785DB48}") = "PlatformSupport", "src\Shared\PlatformSupport\PlatformSupport.shproj", "{E4D9629C-F168-4224-3F51-A5E482FFBC42}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Perspex.Markup", "src\Markup\Perspex.Markup\Perspex.Markup.csproj", "{6417E941-21BC-467B-A771-0DE389353CE6}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Perspex.Markup.UnitTests", "tests\Perspex.Markup.UnitTests\Perspex.Markup.UnitTests.csproj", "{8EF392D5-1416-45AA-9956-7CBBC3229E8A}"
+EndProject
 Global
 	GlobalSection(SharedMSBuildProjectFiles) = preSolution
 		src\Shared\PlatformSupport\PlatformSupport.projitems*{e4d9629c-f168-4224-3f51-a5e482ffbc42}*SharedItemsImports = 13
@ -235,6 +239,14 @@ Global
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 		{5FB2B005-0A7F-4DAD-ADD4-3ED01444E63D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{6417E941-21BC-467B-A771-0DE389353CE6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{6417E941-21BC-467B-A771-0DE389353CE6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{6417E941-21BC-467B-A771-0DE389353CE6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{6417E941-21BC-467B-A771-0DE389353CE6}.Release|Any CPU.Build.0 = Release|Any CPU
+		{8EF392D5-1416-45AA-9956-7CBBC3229E8A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{8EF392D5-1416-45AA-9956-7CBBC3229E8A}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{8EF392D5-1416-45AA-9956-7CBBC3229E8A}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{8EF392D5-1416-45AA-9956-7CBBC3229E8A}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@ -260,5 +272,7 @@ Global
 		{54F237D5-A70A-4752-9656-0C70B1A7B047} = {B9894058-278A-46B5-B6ED-AD613FCC03B3}
 		{FB05AC90-89BA-4F2F-A924-F37875FB547C} = {B9894058-278A-46B5-B6ED-AD613FCC03B3}
 		{E4D9629C-F168-4224-3F51-A5E482FFBC42} = {A689DEF5-D50F-4975-8B72-124C9EB54066}
+		{6417E941-21BC-467B-A771-0DE389353CE6} = {8B6A8209-894F-4BA1-B880-965FD453982C}
+		{8EF392D5-1416-45AA-9956-7CBBC3229E8A} = {C5A00AC3-B34C-4564-9BDD-2DA473EF4D8B}
 	EndGlobalSection
 EndGlobal
--- a/Perspex.v2.ncrunchsolution
+++ b/Perspex.v2.ncrunchsolution
--- a/src/Markup/Perspex.Markup/Binding/ExpressionNode.cs
+++ b/src/Markup/Perspex.Markup/Binding/ExpressionNode.cs
@ -0,0 +1,103 @@
+// 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.Subjects;
+
+namespace Perspex.Markup.Binding
+{
+    public abstract class ExpressionNode : IObservable<ExpressionValue>
+    {
+        private object _target;
+
+        private Subject<ExpressionValue> _subject;
+
+        private ExpressionValue _value = ExpressionValue.None;
+
+        public ExpressionNode Next
+        {
+            get;
+            set;
+        }
+
+        public object Target
+        {
+            get { return _target; }
+            set
+            {
+                if (_target != null)
+                {
+                    Unsubscribe(_target);
+                }
+
+                _target = value;
+
+                if (_target != null)
+                {
+                    Subscribe(_target);
+                }
+                else
+                {
+                    CurrentValue = ExpressionValue.None;
+                }
+
+                if (Next != null)
+                {
+                    Next.Target = CurrentValue.Value;
+                }
+            }
+        }
+
+        public ExpressionValue CurrentValue
+        {
+            get
+            {
+                return _value;
+            }
+
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException("value");
+                }
+
+                _value = value;
+
+                if (Next != null)
+                {
+                    Next.Target = value.Value;
+                }
+
+                if (_subject != null)
+                {
+                    _subject.OnNext(value);
+                }
+            }
+        }
+
+        public IDisposable Subscribe(IObserver<ExpressionValue> observer)
+        {
+            if (Next != null)
+            {
+                return Next.Subscribe(observer);
+            }
+            else
+            {
+                if (_subject == null)
+                {
+                    _subject = new Subject<ExpressionValue>();
+                }
+
+                observer.OnNext(CurrentValue);
+                return _subject.Subscribe(observer);
+            }
+        }
+
+        protected abstract void Subscribe(object target);
+
+        protected abstract void Unsubscribe(object target);
+
+    }
+}
--- a/src/Markup/Perspex.Markup/Binding/ExpressionNodeBuilder.cs
+++ b/src/Markup/Perspex.Markup/Binding/ExpressionNodeBuilder.cs
@ -0,0 +1,74 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace Perspex.Markup.Binding
+{
+    public class ExpressionNodeBuilder
+    {
+        public static IList<ExpressionNode> Build(string expression)
+        {
+            if (string.IsNullOrWhiteSpace(expression))
+            {
+                throw new ArgumentException("'expression' may not be empty.");
+            }
+
+            var syntaxTree = CSharpSyntaxTree.ParseText(expression, new CSharpParseOptions(kind: SourceCodeKind.Interactive));
+            var syntaxRoot = syntaxTree.GetRoot();
+            var syntax = syntaxRoot.ChildNodes().SingleOrDefault()?.ChildNodes()?.SingleOrDefault() as ExpressionStatementSyntax;
+
+            if (syntax != null)
+            {
+                var result = new List<ExpressionNode>();
+
+                foreach (SyntaxNode node in syntax.ChildNodes())
+                {
+                    var identifier = node as IdentifierNameSyntax;
+                    var memberAccess = node as MemberAccessExpressionSyntax;
+
+                    if (identifier != null)
+                    {
+                        result.Add(new PropertyAccessorNode(identifier.Identifier.ValueText));
+                    }
+                    else if (memberAccess != null)
+                    {
+                        Build(memberAccess, result);
+                    }
+                }
+
+                for (int i = 0; i < result.Count - 1; ++i)
+                {
+                    result[i].Next = result[i + 1];
+                }
+
+                return result;
+            }
+            else
+            {
+                throw new Exception($"Invalid expression: {expression}");
+            }
+        }
+
+        private static void Build(MemberAccessExpressionSyntax syntax, IList<ExpressionNode> result)
+        {
+            foreach (SyntaxNode node in syntax.ChildNodes())
+            {
+                var identifier = node as IdentifierNameSyntax;
+                var memberAccess = node as MemberAccessExpressionSyntax;
+
+                if (identifier != null)
+                {
+                    result.Add(new PropertyAccessorNode(identifier.Identifier.ValueText));
+                }
+                else if (memberAccess != null)
+                {
+                    Build(memberAccess, result);
+                }
+            }
+        }
+    }
+}
--- a/src/Markup/Perspex.Markup/Binding/ExpressionObserver.cs
+++ b/src/Markup/Perspex.Markup/Binding/ExpressionObserver.cs
@ -0,0 +1,55 @@
+// 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.Linq;
+using System.Reactive;
+using System.Reactive.Disposables;
+
+namespace Perspex.Markup.Binding
+{
+    public class ExpressionObserver : ObservableBase<ExpressionValue>
+    {
+        private int _count;
+
+        public ExpressionObserver(object root, string expression)
+        {
+            Root = root;
+            Nodes = ExpressionNodeBuilder.Build(expression);
+        }
+
+        public object Root { get; }
+
+        public IList<ExpressionNode> Nodes { get; }
+
+        protected override IDisposable SubscribeCore(IObserver<ExpressionValue> observer)
+        {
+            IncrementCount();
+
+            var subscription = Nodes[0].Subscribe(observer);
+
+            return Disposable.Create(() =>
+            {
+                DecrementCount();
+                subscription.Dispose();
+            });
+        }
+
+        private void IncrementCount()
+        {
+            if (_count++ == 0)
+            {
+                Nodes[0].Target = Root;
+            }
+        }
+
+        private void DecrementCount()
+        {
+            if (--_count == 0)
+            {
+                Nodes[0].Target = null;
+            }
+        }
+    }
+}
--- a/src/Markup/Perspex.Markup/Binding/ExpressionValue.cs
+++ b/src/Markup/Perspex.Markup/Binding/ExpressionValue.cs
@ -0,0 +1,26 @@
+// 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.Markup.Binding
+{
+    public class ExpressionValue
+    {
+        public static readonly ExpressionValue None = new ExpressionValue();
+
+        public ExpressionValue(object value)
+        {
+            HasValue = true;
+            Value = value;
+        }
+
+        private ExpressionValue()
+        {
+            HasValue = false;
+        }
+
+        public bool HasValue { get; }
+        public object Value { get; }
+    }
+}
--- a/src/Markup/Perspex.Markup/Binding/PropertyAccessorNode.cs
+++ b/src/Markup/Perspex.Markup/Binding/PropertyAccessorNode.cs
@ -0,0 +1,67 @@
+// 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.ComponentModel;
+using System.Reflection;
+
+namespace Perspex.Markup.Binding
+{
+    public class PropertyAccessorNode : ExpressionNode
+    {
+        private PropertyInfo _propertyInfo;
+
+        public PropertyAccessorNode(string propertyName)
+        {
+            PropertyName = propertyName;
+        }
+
+        public string PropertyName { get; }
+
+        protected override void Subscribe(object target)
+        {
+            var result = ExpressionValue.None;
+
+            if (target != null)
+            {
+                _propertyInfo = target.GetType().GetTypeInfo().GetDeclaredProperty(PropertyName);
+
+                if (_propertyInfo != null)
+                {
+                    result = new ExpressionValue(_propertyInfo.GetValue(target));
+
+                    var inpc = target as INotifyPropertyChanged;
+
+                    if (inpc != null)
+                    {
+                        inpc.PropertyChanged += PropertyChanged;
+                    }
+                }
+            }
+            else
+            {
+                _propertyInfo = null;
+            }
+
+            CurrentValue = result;
+        }
+
+        private void PropertyChanged(object sender, PropertyChangedEventArgs e)
+        {
+            if (e.PropertyName == PropertyName)
+            {
+                CurrentValue = new ExpressionValue(_propertyInfo.GetValue(Target));
+            }
+        }
+
+        protected override void Unsubscribe(object target)
+        {
+            var inpc = target as INotifyPropertyChanged;
+
+            if (inpc != null)
+            {
+                inpc.PropertyChanged -= PropertyChanged;
+            }
+        }
+    }
+}
--- a/src/Markup/Perspex.Markup/Perspex.Markup.csproj
+++ b/src/Markup/Perspex.Markup/Perspex.Markup.csproj
@ -0,0 +1,93 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+  <PropertyGroup>
+    <MinimumVisualStudioVersion>11.0</MinimumVisualStudioVersion>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <ProjectGuid>{6417E941-21BC-467B-A771-0DE389353CE6}</ProjectGuid>
+    <OutputType>Library</OutputType>
+    <AppDesignerFolder>Properties</AppDesignerFolder>
+    <RootNamespace>Perspex.Markup</RootNamespace>
+    <AssemblyName>Perspex.Markup</AssemblyName>
+    <DefaultLanguage>en-US</DefaultLanguage>
+    <FileAlignment>512</FileAlignment>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <TargetFrameworkProfile>Profile7</TargetFrameworkProfile>
+    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+    <DebugSymbols>true</DebugSymbols>
+    <DebugType>full</DebugType>
+    <Optimize>false</Optimize>
+    <OutputPath>bin\Debug\</OutputPath>
+    <DefineConstants>DEBUG;TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+    <DebugType>pdbonly</DebugType>
+    <Optimize>true</Optimize>
+    <OutputPath>bin\Release\</OutputPath>
+    <DefineConstants>TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Binding\ExpressionNodeBuilder.cs" />
+    <Compile Include="Binding\ExpressionValue.cs" />
+    <Compile Include="Binding\PropertyAccessorNode.cs" />
+    <Compile Include="Binding\ExpressionNode.cs" />
+    <Compile Include="Binding\ExpressionObserver.cs" />
+    <Compile Include="Properties\AssemblyInfo.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Reference Include="Microsoft.CodeAnalysis, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
+      <HintPath>..\..\..\packages\Microsoft.CodeAnalysis.Common.1.1.0-beta1-20150812-01\lib\portable-net45+win8\Microsoft.CodeAnalysis.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="Microsoft.CodeAnalysis.CSharp, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
+      <HintPath>..\..\..\packages\Microsoft.CodeAnalysis.CSharp.1.1.0-beta1-20150812-01\lib\portable-net45+win8\Microsoft.CodeAnalysis.CSharp.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="System.Collections.Immutable, Version=1.1.36.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
+      <HintPath>..\..\..\packages\System.Collections.Immutable.1.1.36\lib\portable-net45+win8+wp8+wpa81\System.Collections.Immutable.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>
+    <Reference Include="System.Reflection.Metadata, Version=1.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
+      <HintPath>..\..\..\packages\System.Reflection.Metadata.1.1.0-alpha-00009\lib\portable-net45+win8\System.Reflection.Metadata.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+  <ItemGroup>
+    <Analyzer Include="..\..\..\packages\Microsoft.CodeAnalysis.Analyzers.1.1.0-beta1-20150812-01\analyzers\dotnet\cs\Microsoft.CodeAnalysis.Analyzers.dll" />
+    <Analyzer Include="..\..\..\packages\Microsoft.CodeAnalysis.Analyzers.1.1.0-beta1-20150812-01\analyzers\dotnet\cs\Microsoft.CodeAnalysis.CSharp.Analyzers.dll" />
+  </ItemGroup>
+  <Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />
+  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
+       Other similar extension points exist, see Microsoft.Common.targets.
+  <Target Name="BeforeBuild">
+  </Target>
+  <Target Name="AfterBuild">
+  </Target>
+  -->
+</Project>
--- a/src/Markup/Perspex.Markup/Properties/AssemblyInfo.cs
+++ b/src/Markup/Perspex.Markup/Properties/AssemblyInfo.cs
@ -0,0 +1,30 @@
+using System.Resources;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following 
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyTitle("Perspex.Markup")]
+[assembly: AssemblyDescription("")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("")]
+[assembly: AssemblyProduct("Perspex.Markup")]
+[assembly: AssemblyCopyright("Copyright ©  2015")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+[assembly: NeutralResourcesLanguage("en")]
+
+// Version information for an assembly consists of the following four values:
+//
+//      Major Version
+//      Minor Version 
+//      Build Number
+//      Revision
+//
+// You can specify all the values or you can default the Build and Revision Numbers 
+// by using the '*' as shown below:
+// [assembly: AssemblyVersion("1.0.*")]
+[assembly: AssemblyVersion("1.0.0.0")]
+[assembly: AssemblyFileVersion("1.0.0.0")]
--- a/src/Markup/Perspex.Markup/packages.config
+++ b/src/Markup/Perspex.Markup/packages.config
@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="Microsoft.CodeAnalysis.Analyzers" version="1.1.0-beta1-20150812-01" targetFramework="portable45-net45+win8" />
+  <package id="Microsoft.CodeAnalysis.Common" version="1.1.0-beta1-20150812-01" targetFramework="portable45-net45+win8" />
+  <package id="Microsoft.CodeAnalysis.CSharp" version="1.1.0-beta1-20150812-01" targetFramework="portable45-net45+win8" />
+  <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="System.Collections.Immutable" version="1.1.36" targetFramework="portable45-net45+win8" />
+  <package id="System.Reflection.Metadata" version="1.1.0-alpha-00009" targetFramework="portable45-net45+win8" />
+</packages>
--- a/tests/Perspex.Markup.UnitTests/Binding/ExpressionNodeBuilderTests.cs
+++ b/tests/Perspex.Markup.UnitTests/Binding/ExpressionNodeBuilderTests.cs
@ -0,0 +1,29 @@
+// 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.Markup.Binding;
+using Xunit;
+
+namespace Perspex.Markup.UnitTests.Binding
+{
+    public class ExpressionNodeBuilderTests
+    {
+        [Fact]
+        public void Should_Build_Single_Property()
+        {
+            var result = ExpressionNodeBuilder.Build("Foo");
+
+            Assert.Equal(1, result.Count);
+            Assert.IsType<PropertyAccessorNode>(result[0]);
+        }
+
+        [Fact]
+        public void Should_Build_Property_Chain()
+        {
+            var result = ExpressionNodeBuilder.Build("Foo.Bar.Baz");
+
+            Assert.Equal(3, result.Count);
+            Assert.IsType<PropertyAccessorNode>(result[0]);
+        }
+    }
+}
--- a/tests/Perspex.Markup.UnitTests/Binding/ExpressionObserverTests.cs
+++ b/tests/Perspex.Markup.UnitTests/Binding/ExpressionObserverTests.cs
@ -0,0 +1,163 @@
+// 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 Perspex.Markup.Binding;
+using Xunit;
+
+namespace Perspex.Markup.UnitTests.Binding
+{
+    public class ExpressionObserverTests
+    {
+        [Fact]
+        public async void Should_Get_Simple_Property_Value()
+        {
+            var data = new { Foo = "foo" };
+            var target = new ExpressionObserver(data, "Foo");
+            var result = await target.Take(1);
+
+            Assert.True(result.HasValue);
+            Assert.Equal("foo", result.Value);
+        }
+
+        [Fact]
+        public async void Should_Get_Simple_Property_Chain()
+        {
+            var data = new { Foo = new { Bar = new { Baz = "baz" } }  };
+            var target = new ExpressionObserver(data, "Foo.Bar.Baz");
+            var result = await target.Take(1);
+
+            Assert.True(result.HasValue);
+            Assert.Equal("baz", result.Value);
+        }
+
+        [Fact]
+        public async void Should_Not_Have_Value_For_Broken_Chain()
+        {
+            var data = new { Foo = new { Bar = 1 } };
+            var target = new ExpressionObserver(data, "Foo.Bar.Baz");
+            var result = await target.Take(1);
+
+            Assert.False(result.HasValue);
+        }
+
+        [Fact]
+        public void Should_Track_Simple_Property_Value()
+        {
+            var data = new Class1 { Foo = "foo" };
+            var target = new ExpressionObserver(data, "Foo");
+            var result = new List<object>();
+
+            var sub = target.Subscribe(x => result.Add(x.Value));
+            data.Foo = "bar";
+
+            Assert.Equal(new[] { "foo", "bar" }, result);
+
+            sub.Dispose();
+
+            Assert.Equal(0, data.SubscriptionCount);
+        }
+
+        [Fact]
+        public void Should_Track_End_Of_Property_Chain_Changing()
+        {
+            var data = new Class1 { Class2 = new Class2 { Bar = "bar" } };
+            var target = new ExpressionObserver(data, "Class2.Bar");
+            var result = new List<object>();
+
+            var sub = target.Subscribe(x => result.Add(x.Value));
+            data.Class2.Bar = "baz";
+
+            Assert.Equal(new[] { "bar", "baz" }, result);
+
+            sub.Dispose();
+
+            Assert.Equal(0, data.SubscriptionCount);
+            Assert.Equal(0, data.Class2.SubscriptionCount);
+        }
+
+        [Fact]
+        public void Should_Track_Middle_Of_Property_Chain_Changing()
+        {
+            var data = new Class1 { Class2 = new Class2 { Bar = "bar" } };
+            var target = new ExpressionObserver(data, "Class2.Bar");
+            var result = new List<object>();
+
+            var sub = target.Subscribe(x => result.Add(x.Value));
+            var old = data.Class2;
+            data.Class2 = new Class2 { Bar = "baz" };
+
+            Assert.Equal(new[] { "bar", "baz" }, result);
+
+            sub.Dispose();
+
+            Assert.Equal(0, data.SubscriptionCount);
+            Assert.Equal(0, data.Class2.SubscriptionCount);
+            Assert.Equal(0, old.SubscriptionCount);
+        }
+
+        [Fact]
+        public void Should_Track_Middle_Of_Property_Chain_Breaking_Then_Mending()
+        {
+            var data = new Class1 { Class2 = new Class2 { Bar = "bar" } };
+            var target = new ExpressionObserver(data, "Class2.Bar");
+            var result = new List<object>();
+
+            var sub = target.Subscribe(x => result.Add(x.Value));
+            var old = data.Class2;
+            data.Class2 = null;
+            data.Class2 = new Class2 { Bar = "baz" };
+
+            Assert.Equal(new[] { "bar", null, "baz" }, result);
+
+            sub.Dispose();
+
+            Assert.Equal(0, data.SubscriptionCount);
+            Assert.Equal(0, data.Class2.SubscriptionCount);
+            Assert.Equal(0, old.SubscriptionCount);
+        }
+
+        private class Class1 : NotifyingBase
+        {
+            private string _foo;
+            private Class2 _class2;
+
+            public string Foo
+            {
+                get { return _foo; }
+                set
+                {
+                    _foo = value;
+                    RaisePropertyChanged(nameof(Foo));
+                }
+            }
+
+            public Class2 Class2
+            {
+                get { return _class2; }
+                set
+                {
+                    _class2 = value;
+                    RaisePropertyChanged(nameof(Class2));
+                }
+            }
+        }
+
+        private class Class2 : NotifyingBase
+        {
+            private string _bar;
+
+            public string Bar
+            {
+                get { return _bar; }
+                set
+                {
+                    _bar = value;
+                    RaisePropertyChanged(nameof(Bar));
+                }
+            }
+        }
+    }
+}
--- a/tests/Perspex.Markup.UnitTests/Binding/NotifyingBase.cs
+++ b/tests/Perspex.Markup.UnitTests/Binding/NotifyingBase.cs
@ -0,0 +1,38 @@
+// 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.ComponentModel;
+
+namespace Perspex.Markup.UnitTests.Binding
+{
+    public class NotifyingBase : INotifyPropertyChanged
+    {
+        private PropertyChangedEventHandler _propertyChanged;
+
+        public event PropertyChangedEventHandler PropertyChanged
+        {
+            add
+            {
+                _propertyChanged += value;
+                ++SubscriptionCount;
+            }
+
+            remove
+            {
+                _propertyChanged -= value;
+                --SubscriptionCount;
+            }
+        }
+
+        public int SubscriptionCount
+        {
+            get;
+            private set;
+        }
+
+        protected void RaisePropertyChanged(string propertyName)
+        {
+            _propertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+    }
+}
--- a/tests/Perspex.Markup.UnitTests/Perspex.Markup.UnitTests.csproj
+++ b/tests/Perspex.Markup.UnitTests/Perspex.Markup.UnitTests.csproj
@ -0,0 +1,103 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="..\..\packages\xunit.runner.visualstudio.2.0.1\build\net20\xunit.runner.visualstudio.props" Condition="Exists('..\..\packages\xunit.runner.visualstudio.2.0.1\build\net20\xunit.runner.visualstudio.props')" />
+  <Import Project="..\..\packages\xunit.core.2.0.0\build\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.core.props" Condition="Exists('..\..\packages\xunit.core.2.0.0\build\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.core.props')" />
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <ProjectGuid>{8EF392D5-1416-45AA-9956-7CBBC3229E8A}</ProjectGuid>
+    <OutputType>Library</OutputType>
+    <AppDesignerFolder>Properties</AppDesignerFolder>
+    <RootNamespace>Perspex.Markup.UnitTests</RootNamespace>
+    <AssemblyName>Perspex.Markup.UnitTests</AssemblyName>
+    <TargetFrameworkVersion>v4.6</TargetFrameworkVersion>
+    <FileAlignment>512</FileAlignment>
+    <NuGetPackageImportStamp>
+    </NuGetPackageImportStamp>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+    <DebugSymbols>true</DebugSymbols>
+    <DebugType>full</DebugType>
+    <Optimize>false</Optimize>
+    <OutputPath>bin\Debug\</OutputPath>
+    <DefineConstants>DEBUG;TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+    <DebugType>pdbonly</DebugType>
+    <Optimize>true</Optimize>
+    <OutputPath>bin\Release\</OutputPath>
+    <DefineConstants>TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <ItemGroup>
+    <Reference Include="System" />
+    <Reference Include="System.Core" />
+    <Reference Include="System.Reactive.Core, Version=2.2.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Rx-Core.2.2.5\lib\net45\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\net45\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\net45\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\net45\System.Reactive.PlatformServices.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="System.Xml.Linq" />
+    <Reference Include="System.Data.DataSetExtensions" />
+    <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.Data" />
+    <Reference Include="System.Net.Http" />
+    <Reference Include="System.Xml" />
+    <Reference Include="xunit.abstractions, Version=2.0.0.0, Culture=neutral, PublicKeyToken=8d05b1bb7a6fdb6c, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\xunit.abstractions.2.0.0\lib\net35\xunit.abstractions.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="xunit.assert, Version=2.0.0.2929, Culture=neutral, PublicKeyToken=8d05b1bb7a6fdb6c, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\xunit.assert.2.0.0\lib\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.assert.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="xunit.core, Version=2.0.0.2929, Culture=neutral, PublicKeyToken=8d05b1bb7a6fdb6c, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\xunit.extensibility.core.2.0.0\lib\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.core.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="Binding\ExpressionObserverTests.cs" />
+    <Compile Include="Binding\ExpressionNodeBuilderTests.cs" />
+    <Compile Include="Properties\AssemblyInfo.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Markup\Perspex.Markup\Perspex.Markup.csproj">
+      <Project>{6417e941-21bc-467b-a771-0de389353ce6}</Project>
+      <Name>Perspex.Markup</Name>
+    </ProjectReference>
+  </ItemGroup>
+  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
+    <PropertyGroup>
+      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
+    </PropertyGroup>
+    <Error Condition="!Exists('..\..\packages\xunit.core.2.0.0\build\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.core.props')" Text="$([System.String]::Format('$(ErrorText)', '..\..\packages\xunit.core.2.0.0\build\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.core.props'))" />
+    <Error Condition="!Exists('..\..\packages\xunit.runner.visualstudio.2.0.1\build\net20\xunit.runner.visualstudio.props')" Text="$([System.String]::Format('$(ErrorText)', '..\..\packages\xunit.runner.visualstudio.2.0.1\build\net20\xunit.runner.visualstudio.props'))" />
+  </Target>
+  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
+       Other similar extension points exist, see Microsoft.Common.targets.
+  <Target Name="BeforeBuild">
+  </Target>
+  <Target Name="AfterBuild">
+  </Target>
+  -->
+</Project>
--- a/tests/Perspex.Markup.UnitTests/Properties/AssemblyInfo.cs
+++ b/tests/Perspex.Markup.UnitTests/Properties/AssemblyInfo.cs
@ -0,0 +1,36 @@
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following 
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyTitle("Perspex.Markup.UnitTests")]
+[assembly: AssemblyDescription("")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("")]
+[assembly: AssemblyProduct("Perspex.Markup.UnitTests")]
+[assembly: AssemblyCopyright("Copyright ©  2015")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+
+// Setting ComVisible to false makes the types in this assembly not visible 
+// to COM components.  If you need to access a type in this assembly from 
+// COM, set the ComVisible attribute to true on that type.
+[assembly: ComVisible(false)]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM
+[assembly: Guid("8ef392d5-1416-45aa-9956-7cbbc3229e8a")]
+
+// Version information for an assembly consists of the following four values:
+//
+//      Major Version
+//      Minor Version 
+//      Build Number
+//      Revision
+//
+// You can specify all the values or you can default the Build and Revision Numbers 
+// by using the '*' as shown below:
+// [assembly: AssemblyVersion("1.0.*")]
+[assembly: AssemblyVersion("1.0.0.0")]
+[assembly: AssemblyFileVersion("1.0.0.0")]
--- a/tests/Perspex.Markup.UnitTests/packages.config
+++ b/tests/Perspex.Markup.UnitTests/packages.config
@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="Rx-Core" version="2.2.5" targetFramework="net46" />
+  <package id="Rx-Interfaces" version="2.2.5" targetFramework="net46" />
+  <package id="Rx-Linq" version="2.2.5" targetFramework="net46" />
+  <package id="Rx-Main" version="2.2.5" targetFramework="net46" />
+  <package id="Rx-PlatformServices" version="2.2.5" targetFramework="net46" />
+  <package id="xunit" version="2.0.0" targetFramework="net46" />
+  <package id="xunit.abstractions" version="2.0.0" targetFramework="net46" />
+  <package id="xunit.assert" version="2.0.0" targetFramework="net46" />
+  <package id="xunit.core" version="2.0.0" targetFramework="net46" />
+  <package id="xunit.extensibility.core" version="2.0.0" targetFramework="net46" />
+  <package id="xunit.runner.visualstudio" version="2.0.1" targetFramework="net46" />
+</packages>