Added test for issue 284.

Moved NotifyingBase to Perspex.UnitTests in order to do this.

tests/Perspex.Controls.UnitTests/Perspex.Controls.UnitTests.csproj

@@ -148,6 +148,10 @@
       <Project>{3e53a01a-b331-47f3-b828-4a5717e77a24}</Project>
       <Name>Perspex.Markup.Xaml</Name>
     </ProjectReference>
+    <ProjectReference Include="..\..\src\Markup\Perspex.Markup\Perspex.Markup.csproj">
+      <Project>{6417e941-21bc-467b-a771-0de389353ce6}</Project>
+      <Name>Perspex.Markup</Name>
+    </ProjectReference>
     <ProjectReference Include="..\..\src\Perspex.Animation\Perspex.Animation.csproj">
       <Project>{D211E587-D8BC-45B9-95A4-F297C8FA5200}</Project>
       <Name>Perspex.Animation</Name>

tests/Perspex.Controls.UnitTests/TreeViewTests.cs

@@ -1,13 +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.Collections.Generic;
 using System.Linq;
 using Perspex.Collections;
 using Perspex.Controls.Presenters;
 using Perspex.Controls.Templates;
+using Perspex.Data;
 using Perspex.Input;
 using Perspex.LogicalTree;
+using Perspex.Markup.Data;
 using Perspex.UnitTests;
 using Xunit;
 
@@ -252,6 +255,36 @@ namespace Perspex.Controls.UnitTests
             Assert.NotNull(NameScope.GetNameScope((TreeViewItem)item));
         }
 
+        [Fact]
+        public void Should_React_To_Children_Changing()
+        {
+            var data = CreateTestTreeData();
+
+            var target = new TreeView
+            {
+                Template = CreateTreeViewTemplate(),
+                Items = data,
+                DataTemplates = CreateNodeDataTemplate(),
+            };
+
+            ApplyTemplates(target);
+
+            Assert.Equal(new[] { "Root" }, ExtractItemHeader(target, 0));
+            Assert.Equal(new[] { "Child1", "Child2" }, ExtractItemHeader(target, 1));
+            Assert.Equal(new[] { "Grandchild2a" }, ExtractItemHeader(target, 2));
+
+            data[0].Children = new PerspexList<Node>
+            {
+                new Node
+                {
+                    Value = "NewChild1",
+                }
+            };
+
+            Assert.Equal(new[] { "Root" }, ExtractItemHeader(target, 0));
+            Assert.Equal(new[] { "NewChild1" }, ExtractItemHeader(target, 1));
+        }
+
         private void ApplyTemplates(TreeView tree)
         {
             tree.ApplyTemplate();
@@ -303,9 +336,7 @@ namespace Perspex.Controls.UnitTests
         {
             return new DataTemplates
             {
-                new FuncTreeDataTemplate<Node>(
-                    x => new TextBlock { Text = x.Value },
-                    x => x.Children),
+                new TestTreeDataTemplate()
             };
         }
 
@@ -360,10 +391,45 @@ namespace Perspex.Controls.UnitTests
             }
         }
 
-        private class Node
+        private class Node :  NotifyingBase
         {
+            private IPerspexList<Node> _children;
+
             public string Value { get; set; }
-            public IPerspexList<Node> Children { get; set; }
+
+            public IPerspexList<Node> Children
+            {
+                get
+                {
+                    return _children;
+                }
+
+                set
+                {
+                    _children = value;
+                    RaisePropertyChanged(nameof(Children));
+                }
+            }
+        }
+
+        private class TestTreeDataTemplate : ITreeDataTemplate
+        {
+            public IControl Build(object param)
+            {
+                var node = (Node)param;
+                return new TextBlock { Text = node.Value };
+            }
+
+            public InstancedBinding ItemsSelector(object item)
+            {
+                var obs = new ExpressionObserver(item, nameof(Node.Children));
+                return new InstancedBinding(obs);
+            }
+
+            public bool Match(object data)
+            {
+                return data is Node;
+            }
         }
     }
 }

tests/Perspex.Markup.UnitTests/Data/ExpressionObserverTests_Indexer.cs

@@ -8,6 +8,7 @@ using System.Reactive.Linq;
 using Perspex.Collections;
 using Perspex.Diagnostics;
 using Perspex.Markup.Data;
+using Perspex.UnitTests;
 using Xunit;
 
 namespace Perspex.Markup.UnitTests.Data

tests/Perspex.Markup.UnitTests/Data/ExpressionObserverTests_Observable.cs

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

tests/Perspex.Markup.UnitTests/Data/ExpressionObserverTests_Property.cs

@@ -8,6 +8,7 @@ using System.Reactive.Linq;
 using System.Reactive.Subjects;
 using Microsoft.Reactive.Testing;
 using Perspex.Markup.Data;
+using Perspex.UnitTests;
 using Xunit;
 
 namespace Perspex.Markup.UnitTests.Data
@@ -385,11 +386,6 @@ namespace Perspex.Markup.UnitTests.Data
                     RaisePropertyChanged(nameof(Next));
                 }
             }
-
-            public void RaisePropertyChanged(string propertyName)
-            {
-                base.RaisePropertyChanged(propertyName);
-            }
         }
 
         private class Class2 : NotifyingBase, INext

tests/Perspex.Markup.UnitTests/Data/ExpressionObserverTests_SetValue.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Reactive.Linq;
 using Perspex.Markup.Data;
+using Perspex.UnitTests;
 using Xunit;
 
 namespace Perspex.Markup.UnitTests.Data

tests/Perspex.Markup.UnitTests/Data/ExpressionObserverTests_Task.cs

@@ -7,6 +7,7 @@ using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Perspex.Markup.Data;
+using Perspex.UnitTests;
 using Xunit;
 
 namespace Perspex.Markup.UnitTests.Data

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

@@ -96,7 +96,6 @@
     <Compile Include="Data\ExpressionObserverTests_SetValue.cs" />
     <Compile Include="Data\ExpressionObserverTests_Task.cs" />
     <Compile Include="Data\ExpressionSubjectTests.cs" />
-    <Compile Include="Data\NotifyingBase.cs" />
     <Compile Include="DefaultValueConverterTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="UnitTestSynchronizationContext.cs" />

tests/Perspex.Markup.UnitTests/Data/NotifyingBase.cs → tests/Perspex.UnitTests/NotifyingBase.cs

@@ -4,7 +4,7 @@
 using System.ComponentModel;
 using System.Linq;
 
-namespace Perspex.Markup.UnitTests.Data
+namespace Perspex.UnitTests
 {
     public class NotifyingBase : INotifyPropertyChanged
     {
@@ -34,7 +34,7 @@ namespace Perspex.Markup.UnitTests.Data
             private set;
         }
 
-        protected void RaisePropertyChanged(string propertyName)
+        public void RaisePropertyChanged(string propertyName)
         {
             _propertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
         }

tests/Perspex.UnitTests/Perspex.UnitTests.csproj

@@ -62,6 +62,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="NotifyingBase.cs" />
     <Compile Include="TestTemplatedRoot.cs" />
     <Compile Include="TestRoot.cs" />
     <Compile Include="TestServices.cs" />