From f1879e1a06d68ca1abe38d09eec71a59420daaea Mon Sep 17 00:00:00 2001
From: Dustin Campbell <dustin@teamcampbell.org>
Date: Fri, 4 Dec 2015 14:30:45 -0800
Subject: [PATCH] Display traits in tree view with check boxes

---
 xunit.runner.wpf/Extensions.FuncComparer.cs   |  20 ++++
 xunit.runner.wpf/Extensions.cs                |  80 ++++++++++++-
 xunit.runner.wpf/FilteredCollectionView.cs    |  12 +-
 xunit.runner.wpf/MainWindow.xaml              |  57 +++++----
 xunit.runner.wpf/ViewModel/MainViewModel.cs   |  36 +++---
 xunit.runner.wpf/ViewModel/SearchQuery.cs     |   8 +-
 .../ViewModel/TestCaseViewModel.cs            |  11 +-
 .../ViewModel/TraitCollectionView.cs          |  56 +++------
 .../ViewModel/TraitViewModel.Comparer.cs      |  20 ++++
 xunit.runner.wpf/ViewModel/TraitViewModel.cs  | 111 +++++++++++++++---
 .../ViewModel/TraitViewModelComparer.cs       |  38 ------
 xunit.runner.wpf/xunit.runner.wpf.csproj      |   3 +-
 12 files changed, 296 insertions(+), 156 deletions(-)
 create mode 100644 xunit.runner.wpf/Extensions.FuncComparer.cs
 create mode 100644 xunit.runner.wpf/ViewModel/TraitViewModel.Comparer.cs
 delete mode 100644 xunit.runner.wpf/ViewModel/TraitViewModelComparer.cs

diff --git a/xunit.runner.wpf/Extensions.FuncComparer.cs b/xunit.runner.wpf/Extensions.FuncComparer.cs
new file mode 100644
index 0000000..5c41ce1
--- /dev/null
+++ b/xunit.runner.wpf/Extensions.FuncComparer.cs
@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+
+namespace xunit.runner.wpf
+{
+    public static partial class Extensions
+    {
+        private class FuncComparer<T> : IComparer<T>
+        {
+            private readonly Func<T, T, int> _comparison;
+
+            public FuncComparer(Func<T, T, int> comparison)
+            {
+                _comparison = comparison;
+            }
+
+            public int Compare(T x, T y) => _comparison(x, y);
+        }
+    }
+}
diff --git a/xunit.runner.wpf/Extensions.cs b/xunit.runner.wpf/Extensions.cs
index 8be16ca..7eb6838 100644
--- a/xunit.runner.wpf/Extensions.cs
+++ b/xunit.runner.wpf/Extensions.cs
@@ -1,13 +1,10 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 namespace xunit.runner.wpf
 {
-    public static class Extensions
+    public static partial class Extensions
     {
         public static void AddRange<TList, TEnumerable>(this ICollection<TList> list, IEnumerable<TEnumerable> items) where TEnumerable : TList
         {
@@ -24,5 +21,80 @@ namespace xunit.runner.wpf
                 list.Add(i);
             }
         }
+
+        public static int BinarySearch<T, TValue>(this ObservableCollection<T> collection, int index, int length, TValue value, IComparer<TValue> comparer, Func<T, TValue> selector)
+        {
+            comparer = comparer ?? Comparer<TValue>.Default;
+
+            var low = index;
+            var high = (index + length) - 1;
+
+            while (low <= high)
+            {
+                var mid = low + ((high - low) / 2);
+                var comp = comparer.Compare(selector(collection[mid]), value);
+
+                if (comp == 0)
+                {
+                    return mid;
+                }
+
+                if (comp < 0)
+                {
+                    low = mid + 1;
+                }
+                else
+                {
+                    high = mid - 1;
+                }
+            }
+
+            return ~low;
+        }
+
+        public static int BinarySearch<T, TValue>(this ObservableCollection<T> collection, TValue value, IComparer<TValue> comparer, Func<T, TValue> selector)
+        {
+            return collection.BinarySearch(0, collection.Count, value, comparer, selector);
+        }
+
+        public static int BinarySearch<T, TValue>(this ObservableCollection<T> collection, int index, int length, TValue value, Func<TValue, TValue, int> comparison, Func<T, TValue> selector)
+        {
+            return collection.BinarySearch(index, length, value, new FuncComparer<TValue>(comparison), selector);
+        }
+
+        public static int BinarySearch<T, TValue>(this ObservableCollection<T> collection, TValue value, Func<TValue, TValue, int> comparison, Func<T, TValue> selector)
+        {
+            return collection.BinarySearch(0, collection.Count, value, new FuncComparer<TValue>(comparison), selector);
+        }
+
+        public static int BinarySearch<T, TValue>(this ObservableCollection<T> collection, TValue value, Func<T, TValue> selector)
+        {
+            return collection.BinarySearch(0, collection.Count, value, comparer: null, selector: selector);
+        }
+
+        public static int BinarySearch<T>(this ObservableCollection<T> collection, int index, int length, T value, IComparer<T> comparer)
+        {
+            return collection.BinarySearch(index, length, value, comparer, x => x);
+        }
+
+        public static int BinarySearch<T>(this ObservableCollection<T> collection, T value, IComparer<T> comparer)
+        {
+            return collection.BinarySearch(0, collection.Count, value, comparer, x => x);
+        }
+
+        public static int BinarySearch<T>(this ObservableCollection<T> collection, T value)
+        {
+            return collection.BinarySearch(0, collection.Count, value, Comparer<T>.Default, x => x);
+        }
+
+        public static int BinarySearch<T>(this ObservableCollection<T> collection, int index, int length, T value, Func<T, T, int> comparison)
+        {
+            return collection.BinarySearch(index, length, value, new FuncComparer<T>(comparison), x => x);
+        }
+
+        public static int BinarySearch<T>(this ObservableCollection<T> collection, T value, Func<T, T, int> comparison)
+        {
+            return collection.BinarySearch(0, collection.Count, value, new FuncComparer<T>(comparison), x => x);
+        }
     }
 }
diff --git a/xunit.runner.wpf/FilteredCollectionView.cs b/xunit.runner.wpf/FilteredCollectionView.cs
index a2e4762..a37ad1a 100644
--- a/xunit.runner.wpf/FilteredCollectionView.cs
+++ b/xunit.runner.wpf/FilteredCollectionView.cs
@@ -45,11 +45,7 @@ namespace xunit.runner.wpf
 
         protected virtual void OnItemChanged(T sender, PropertyChangedEventArgs args)
         {
-            var itemChanged = this.ItemChanged;
-            if (itemChanged != null)
-            {
-                itemChanged(sender, args);
-            }
+            this.ItemChanged?.Invoke(sender, args);
         }
 
         private TFilterArg filterArgument;
@@ -187,11 +183,7 @@ namespace xunit.runner.wpf
 
         protected void OnCollectionChanged(NotifyCollectionChangedEventArgs args)
         {
-            var collectionChanged = this.CollectionChanged;
-            if (collectionChanged != null)
-            {
-                collectionChanged(this, args);
-            }
+            this.CollectionChanged?.Invoke(this, args);
         }
 
         public void Add(T item)
diff --git a/xunit.runner.wpf/MainWindow.xaml b/xunit.runner.wpf/MainWindow.xaml
index 6c8055d..67cae1c 100644
--- a/xunit.runner.wpf/MainWindow.xaml
+++ b/xunit.runner.wpf/MainWindow.xaml
@@ -119,13 +119,13 @@
                                 </StackPanel>
                             </DataTemplate>
                         </ListBox.ItemTemplate>
-                        
+
                         <ListBox.ItemContainerStyle>
                             <Style TargetType="{x:Type ListBoxItem}">
                                 <Setter Property="IsSelected" Value="{Binding Mode=TwoWay, Path=IsSelected}"/>
                             </Style>
                         </ListBox.ItemContainerStyle>
-                        
+
                         <ListBox.ContextMenu>
                             <ContextMenu>
                                 <MenuItem Header="Reload" Command="{Binding AssemblyReloadCommand}" />
@@ -139,29 +139,44 @@
 
                     <Label Content="Traits:"
                            Grid.Row="4" />
-                    <ListBox Grid.Row="5"
-                             ItemsSource="{Binding Traits}">
-                        <ListBox.ItemTemplate>
-                            <DataTemplate DataType="vm:TraitViewModel">
-                                <TextBlock Text="{Binding DisplayName}" />
-                            </DataTemplate>
-                        </ListBox.ItemTemplate>
-                        <ListBox.ItemContainerStyle>
-                            <Style TargetType="{x:Type ListBoxItem}">
-                                <Setter Property="IsSelected" Value="{Binding Mode=TwoWay, Path=IsSelected}"/>
+
+                    <TreeView Grid.Row="5"
+                              ItemsSource="{Binding Traits}">
+
+                        <TreeView.Resources>
+                            <HierarchicalDataTemplate DataType="{x:Type vm:TraitViewModel}"
+                                                      ItemsSource="{Binding Children}">
+
+                                <CheckBox IsChecked="{Binding IsChecked}" Content="{Binding Text}" >
+                                    <i:Interaction.Triggers>
+                                        <i:EventTrigger EventName="Checked">
+                                            <cmd:EventToCommand Command="{Binding DataContext.TraitCheckedChangedCommand, RelativeSource={RelativeSource AncestorType=Window}}"
+                                                                CommandParameter="{Binding}" />
+                                        </i:EventTrigger>
+
+                                        <i:EventTrigger EventName="Unchecked">
+                                            <cmd:EventToCommand Command="{Binding DataContext.TraitCheckedChangedCommand, RelativeSource={RelativeSource AncestorType=Window}}"
+                                                                CommandParameter="{Binding}" />
+                                        </i:EventTrigger>
+                                    </i:Interaction.Triggers>
+                                </CheckBox>
+
+                            </HierarchicalDataTemplate>
+                        </TreeView.Resources>
+
+                        <TreeView.ItemContainerStyle>
+                            <Style TargetType="TreeViewItem">
+                                <Setter Property="IsExpanded" Value="{Binding IsExpanded}" />
                             </Style>
-                        </ListBox.ItemContainerStyle>
-                        <ListBox.ContextMenu>
+                        </TreeView.ItemContainerStyle>
+
+                        <TreeView.ContextMenu>
                             <ContextMenu>
                                 <MenuItem Header="Clear" Command="{Binding TraitsClearCommand}" />
                             </ContextMenu>
-                        </ListBox.ContextMenu>
-                        <i:Interaction.Triggers>
-                            <i:EventTrigger EventName="SelectionChanged">
-                                <cmd:EventToCommand Command="{Binding TraitSelectionChangedCommand}" />
-                            </i:EventTrigger>
-                        </i:Interaction.Triggers>
-                    </ListBox>
+                        </TreeView.ContextMenu>
+
+                    </TreeView>
                 </Grid>
             </GroupBox>
 
diff --git a/xunit.runner.wpf/ViewModel/MainViewModel.cs b/xunit.runner.wpf/ViewModel/MainViewModel.cs
index 9c92716..c79b0f9 100644
--- a/xunit.runner.wpf/ViewModel/MainViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/MainViewModel.cs
@@ -50,7 +50,7 @@ namespace xunit.runner.wpf.ViewModel
             this.WindowLoadedCommand = new RelayCommand(OnExecuteWindowLoaded);
             this.RunCommand = new RelayCommand(OnExecuteRun, CanExecuteRun);
             this.CancelCommand = new RelayCommand(OnExecuteCancel, CanExecuteCancel);
-            this.TraitSelectionChangedCommand = new RelayCommand(OnExecuteTraitSelectionChanged);
+            this.TraitCheckedChangedCommand = new RelayCommand<TraitViewModel>(OnExecuteTraitCheckedChanged);
             this.TraitsClearCommand = new RelayCommand(OnExecuteTraitsClear);
             this.AssemblyReloadCommand = new RelayCommand(OnExecuteAssemblyReload, CanExecuteAssemblyReload);
             this.AssemblyReloadAllCommand = new RelayCommand(OnExecuteAssemblyReloadAll);
@@ -113,6 +113,7 @@ namespace xunit.runner.wpf.ViewModel
         public ICommand WindowLoadedCommand { get; }
         public RelayCommand RunCommand { get; }
         public RelayCommand CancelCommand { get; }
+        public ICommand TraitCheckedChangedCommand { get; }
         public ICommand TraitSelectionChangedCommand { get; }
         public ICommand TraitsClearCommand { get; }
         public ICommand AssemblyReloadCommand { get; }
@@ -354,7 +355,7 @@ namespace xunit.runner.wpf.ViewModel
             this.traitCollectionView.Collection.Clear();
             foreach (var testCase in this.allTestCases)
             {
-                this.traitCollectionView.Add(testCase.Traits);
+                this.traitCollectionView.AddRange(testCase.Traits);
             }
         }
 
@@ -476,18 +477,18 @@ namespace xunit.runner.wpf.ViewModel
             }
         }
 
-        private void OnTestDiscovered(List<TestCaseData> testCaseData)
+        private void OnTestDiscovered(List<TestCaseData> testCaseDataList)
         {
             var allTraits = new SortedDictionary<string, SortedSet<string>>();
-            foreach (var data in testCaseData)
+            foreach (var data in testCaseDataList)
             {
                 AddTraits(allTraits, data);
             }
 
-            this.allTestCases.AddRange(testCaseData.Select(d =>
-                new TestCaseViewModel(d.DisplayName, d.AssemblyPath, Convert(CreateSortedTraits(d)).ToImmutableArray())));
-            
-            this.traitCollectionView.Add(Convert(allTraits));
+            this.allTestCases.AddRange(testCaseDataList.Select(d =>
+                new TestCaseViewModel(d.DisplayName, d.AssemblyPath, Convert(CreateSortedTraits(d)))));
+
+            this.traitCollectionView.AddRange(Convert(allTraits));
         }
 
         private SortedDictionary<string, SortedSet<string>> CreateSortedTraits(TestCaseData data)
@@ -499,7 +500,16 @@ namespace xunit.runner.wpf.ViewModel
 
         private static IEnumerable<TraitViewModel> Convert(SortedDictionary<string, SortedSet<string>> allTraits)
         {
-            return allTraits.SelectMany(pair => pair.Value.Select(value => new TraitViewModel(pair.Key, value)));
+            foreach (var trait in allTraits)
+            {
+                var name = trait.Key;
+                var values = trait.Value;
+
+                var viewModel = new TraitViewModel(name);
+                viewModel.AddValues(values);
+
+                yield return viewModel;
+            }
         }
 
         private static void AddTraits(SortedDictionary<string, SortedSet<string>> allTraits, TestCaseData data)
@@ -562,11 +572,9 @@ namespace xunit.runner.wpf.ViewModel
             this.cancellationTokenSource.Cancel();
         }
 
-        private void OnExecuteTraitSelectionChanged()
+        private void OnExecuteTraitCheckedChanged(TraitViewModel trait)
         {
-            this.searchQuery.TraitSet = new HashSet<TraitViewModel>(
-                this.traitCollectionView.Collection.Where(x => x.IsSelected),
-                TraitViewModelComparer.Instance);
+            this.searchQuery.TraitSet = this.traitCollectionView.GetCheckedTraits();
             FilterAfterDelay();
         }
 
@@ -574,7 +582,7 @@ namespace xunit.runner.wpf.ViewModel
         {
             foreach (var cur in this.traitCollectionView.Collection)
             {
-                cur.IsSelected = false;
+                cur.IsChecked = false;
             }
         }
 
diff --git a/xunit.runner.wpf/ViewModel/SearchQuery.cs b/xunit.runner.wpf/ViewModel/SearchQuery.cs
index 5900b67..cc608e6 100644
--- a/xunit.runner.wpf/ViewModel/SearchQuery.cs
+++ b/xunit.runner.wpf/ViewModel/SearchQuery.cs
@@ -1,8 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
+using System.Collections.Generic;
 
 namespace xunit.runner.wpf.ViewModel
 {
@@ -12,6 +8,6 @@ namespace xunit.runner.wpf.ViewModel
         public bool IncludePassedTests = true;
         public bool IncludeSkippedTests = true;
         public string SearchString = string.Empty;
-        public HashSet<TraitViewModel> TraitSet = new HashSet<TraitViewModel>(TraitViewModelComparer.Instance);
+        public ISet<TraitViewModel> TraitSet = new HashSet<TraitViewModel>(TraitViewModel.EqualityComparer);
     }
 }
diff --git a/xunit.runner.wpf/ViewModel/TestCaseViewModel.cs b/xunit.runner.wpf/ViewModel/TestCaseViewModel.cs
index 60f04b4..fa46138 100644
--- a/xunit.runner.wpf/ViewModel/TestCaseViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/TestCaseViewModel.cs
@@ -1,12 +1,7 @@
 using GalaSoft.MvvmLight;
-using System;
-using System.Collections.Generic;
 using System.Collections.Immutable;
-using System.IO;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 using xunit.runner.data;
+using System.Collections.Generic;
 
 namespace xunit.runner.wpf.ViewModel
 {
@@ -14,11 +9,11 @@ namespace xunit.runner.wpf.ViewModel
     {
         private TestState _state = TestState.NotRun;
 
-        public TestCaseViewModel(string displayName, string assemblyFileName, ImmutableArray<TraitViewModel> traits)
+        public TestCaseViewModel(string displayName, string assemblyFileName, IEnumerable<TraitViewModel> traits)
         {
             this.DisplayName = displayName;
             this.AssemblyFileName = assemblyFileName;
-            this.Traits = traits;
+            this.Traits = traits.ToImmutableArray();
         }
 
         public string DisplayName { get; }
diff --git a/xunit.runner.wpf/ViewModel/TraitCollectionView.cs b/xunit.runner.wpf/ViewModel/TraitCollectionView.cs
index f7227cc..fb5610b 100644
--- a/xunit.runner.wpf/ViewModel/TraitCollectionView.cs
+++ b/xunit.runner.wpf/ViewModel/TraitCollectionView.cs
@@ -1,54 +1,36 @@
-using System;
-using System.Collections.Generic;
-using System.Collections.Immutable;
+using System.Collections.Generic;
 using System.Collections.ObjectModel;
-using System.Collections.Specialized;
 using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 namespace xunit.runner.wpf.ViewModel
 {
     public sealed partial class TraitCollectionView
     {
-        private readonly TraitViewModelComparer _comparer = TraitViewModelComparer.Instance;
-        private readonly ObservableCollection<TraitViewModel> _collection = new ObservableCollection<TraitViewModel>();
+        public ObservableCollection<TraitViewModel> Collection { get; } = new ObservableCollection<TraitViewModel>();
 
-        public ObservableCollection<TraitViewModel> Collection => _collection;
-
-        public TraitCollectionView()
+        public void AddRange(IEnumerable<TraitViewModel> traits)
         {
-
-        }
-
-        public void Add(IEnumerable<TraitViewModel> traitList)
-        {
-            foreach (var traitViewModel in traitList)
+            foreach (var trait in traits)
             {
-                InsertIfNotPresent(traitViewModel);
+                var index = Collection.BinarySearch(trait, TraitViewModel.Comparer);
+                if (index < 0)
+                {
+                    Collection.Insert(~index, trait);
+                }
+                else
+                {
+                    // This trait already exists, add more values.
+                    var originalTrait = Collection[index];
+                    originalTrait.AddValues(trait.Children.Select(x => x.Text));
+                }
             }
         }
 
-        private void InsertIfNotPresent(TraitViewModel trait)
+        public ISet<TraitViewModel> GetCheckedTraits()
         {
-            // TODO: make it a binary search
-            for (int i = 0; i < _collection.Count; i++)
-            {
-                var current = _collection[i];
-                var result = _comparer.Compare(trait, current);
-                if (result < 0)
-                {
-                    _collection.Insert(i, trait);
-                    return;
-                }
-
-                if (result == 0)
-                {
-                    return;
-                }
-            }
-
-            _collection.Add(trait);
+            return new HashSet<TraitViewModel>(
+                Collection.SelectMany(x => x.Children).Where(x => x.IsChecked == true),
+                comparer: TraitViewModel.EqualityComparer);
         }
     }
 }
diff --git a/xunit.runner.wpf/ViewModel/TraitViewModel.Comparer.cs b/xunit.runner.wpf/ViewModel/TraitViewModel.Comparer.cs
new file mode 100644
index 0000000..911aa3c
--- /dev/null
+++ b/xunit.runner.wpf/ViewModel/TraitViewModel.Comparer.cs
@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+
+namespace xunit.runner.wpf.ViewModel
+{
+    public partial class TraitViewModel
+    {
+        private static readonly TraitViewModelComparer _comparer = new TraitViewModelComparer();
+
+        internal static IComparer<TraitViewModel> Comparer => _comparer;
+        internal static IEqualityComparer<TraitViewModel> EqualityComparer => _comparer;
+
+        private class TraitViewModelComparer : IEqualityComparer<TraitViewModel>, IComparer<TraitViewModel>
+        {
+            public int Compare(TraitViewModel x, TraitViewModel y) => StringComparer.Ordinal.Compare(x.Text, y.Text);
+            public bool Equals(TraitViewModel x, TraitViewModel y) => StringComparer.Ordinal.Equals(x.Text, y.Text);
+            public int GetHashCode(TraitViewModel obj) => obj.Text.GetHashCode();
+        }
+    }
+}
diff --git a/xunit.runner.wpf/ViewModel/TraitViewModel.cs b/xunit.runner.wpf/ViewModel/TraitViewModel.cs
index 006dc6f..526bfdd 100644
--- a/xunit.runner.wpf/ViewModel/TraitViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/TraitViewModel.cs
@@ -1,31 +1,108 @@
-using GalaSoft.MvvmLight;
-using System;
+using System;
 using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
+using System.Collections.ObjectModel;
+using GalaSoft.MvvmLight;
 
 namespace xunit.runner.wpf.ViewModel
 {
-    public sealed class TraitViewModel : ViewModelBase
+    public partial class TraitViewModel : ViewModelBase
     {
-        private bool _isSelected;
+        private readonly TraitViewModel _parent;
+        private bool? _isChecked;
+        private bool _isExpanded;
+        private string _text;
 
-        public string Name { get; }
-        public string Value { get; }
-        public string DisplayName { get; }
+        public ObservableCollection<TraitViewModel> Children { get; }
 
-        public bool IsSelected
+        public TraitViewModel(string text)
+            : this(null, text)
         {
-            get { return _isSelected; }
-            set { Set(ref _isSelected, value); }
         }
 
-        public TraitViewModel(string name, string value)
+        private TraitViewModel(TraitViewModel parent, string text)
         {
-            Name = name;
-            Value = value;
-            DisplayName = $"{Name}={Value}";
+            this._parent = parent;
+            this._isChecked = false;
+            this._isExpanded = true;
+            this._text = text;
+            this.Children = new ObservableCollection<TraitViewModel>();
+        }
+
+        private void SetIsChecked(bool? value, bool updateChildren, bool updateParent)
+        {
+            if (value == this._isChecked)
+            {
+                return;
+            }
+
+            this._isChecked = value;
+
+            if (updateChildren && value != null)
+            {
+                foreach (var child in this.Children)
+                {
+                    child.SetIsChecked(value, updateChildren: true, updateParent: false);
+                }
+            }
+
+            if (updateParent && _parent != null)
+            {
+                _parent.VerifyCheckState();
+            }
+
+            this.RaisePropertyChanged(nameof(IsChecked));
+        }
+
+        private void VerifyCheckState()
+        {
+            bool? state = null;
+            var isFirst = true;
+
+            foreach (var child in this.Children)
+            {
+                if (isFirst)
+                {
+                    state = child.IsChecked;
+                    isFirst = false;
+                }
+                else if (state != child.IsChecked)
+                {
+                    state = null;
+                    break;
+                }
+            }
+
+            this.SetIsChecked(state, updateChildren: false, updateParent: true);
+        }
+
+        public void AddValues(IEnumerable<string> values)
+        {
+            foreach (var value in values)
+            {
+                var index = this.Children.BinarySearch(value, StringComparer.Ordinal.Compare, v => v.Text);
+                if (index < 0)
+                {
+                    this.Children.Insert(~index, new TraitViewModel(this, value));
+                }
+            }
+        }
+
+        public bool? IsChecked
+        {
+            get { return _isChecked; }
+            set { SetIsChecked(value, updateChildren: true, updateParent: true); }
+        }
+
+        public bool IsExpanded
+        {
+            get { return _isExpanded; }
+            set { Set(ref _isExpanded, value); }
+        }
+
+        public string Text
+        {
+            get { return _text; }
+            set { Set(ref _text, value); }
         }
     }
 }
diff --git a/xunit.runner.wpf/ViewModel/TraitViewModelComparer.cs b/xunit.runner.wpf/ViewModel/TraitViewModelComparer.cs
deleted file mode 100644
index 9970a0a..0000000
--- a/xunit.runner.wpf/ViewModel/TraitViewModelComparer.cs
+++ /dev/null
@@ -1,38 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Collections.Specialized;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace xunit.runner.wpf.ViewModel
-{
-    internal sealed class TraitViewModelComparer : IEqualityComparer<TraitViewModel>, IComparer<TraitViewModel>
-    {
-        internal static readonly TraitViewModelComparer Instance = new TraitViewModelComparer();
-
-        private readonly StringComparer _comparer = StringComparer.Ordinal;
-
-        public int Compare(TraitViewModel x, TraitViewModel y)
-        {
-            var result = _comparer.Compare(x.Name, y.Name);
-            if (result != 0)
-            {
-                return result;
-            }
-
-            return _comparer.Compare(x.Value, y.Value);
-        }
-
-        public bool Equals(TraitViewModel x, TraitViewModel y)
-        {
-            return _comparer.Equals(x.Name, y.Name)
-                && _comparer.Equals(x.Value, y.Value);
-        }
-
-        public int GetHashCode(TraitViewModel obj)
-        {
-            return obj.Name.GetHashCode();
-        }
-    }
-}
diff --git a/xunit.runner.wpf/xunit.runner.wpf.csproj b/xunit.runner.wpf/xunit.runner.wpf.csproj
index fa17bc8..81ef685 100644
--- a/xunit.runner.wpf/xunit.runner.wpf.csproj
+++ b/xunit.runner.wpf/xunit.runner.wpf.csproj
@@ -102,14 +102,15 @@
     </Compile>
     <Compile Include="Storage.cs" />
     <Compile Include="Storage.WindowPlacement.cs" />
+    <Compile Include="Extensions.FuncComparer.cs" />
     <Compile Include="ViewModel\TraitCollectionView.cs" />
     <Compile Include="ViewModel\AssemblyAndConfigFile.cs" />
     <Compile Include="ViewModel\MainViewModel.cs" />
     <Compile Include="ViewModel\SearchQuery.cs" />
     <Compile Include="ViewModel\TestCaseViewModel.cs" />
     <Compile Include="ViewModel\TestAssemblyViewModel.cs" />
+    <Compile Include="ViewModel\TraitViewModel.Comparer.cs" />
     <Compile Include="ViewModel\TraitViewModel.cs" />
-    <Compile Include="ViewModel\TraitViewModelComparer.cs" />
     <Compile Include="ViewModel\ViewModelLocator.cs" />
     <Page Include="LoadingDialog.xaml">
       <SubType>Designer</SubType>