Don't display [None] twice.

src/GitHub.App/SampleData/PullRequestListViewModelDesigner.cs

@@ -44,7 +44,7 @@ public PullRequestListViewModelDesigner()
             SelectedAuthor = Authors.ElementAt(1);
         }
 
-        public ObservableCollection<IPullRequestModel> PullRequests { get; set; }
+        public ITrackingCollection<IPullRequestModel> PullRequests { get; set; }
         public IPullRequestModel SelectedPullRequest { get; set; }
         public ICommand OpenPullRequest { get; set; }
 

src/GitHub.App/ViewModels/PullRequestListViewModel.cs

@@ -1,22 +1,18 @@
-using GitHub.Exports;
-using System;
+using System;
 using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using GitHub.Models;
 using System.Collections.ObjectModel;
-using ReactiveUI;
-using NullGuard;
 using System.ComponentModel.Composition;
-using GitHub.Services;
+using System.Linq;
 using System.Reactive.Linq;
-using GitHub.Extensions.Reactive;
-using System.Windows.Data;
-using GitHub.Collections;
 using System.Windows.Input;
-using GitHub.UI;
 using System.Windows.Media.Imaging;
+using GitHub.Collections;
+using GitHub.Exports;
+using GitHub.Models;
+using GitHub.Services;
+using GitHub.UI;
+using NullGuard;
+using ReactiveUI;
 
 namespace GitHub.ViewModels
 {
@@ -59,11 +55,11 @@ public PullRequestListViewModel(IRepositoryHost repositoryHost, ISimpleRepositor
                 .Subscribe(s => UpdateFilter(s, SelectedAssignee, SelectedAuthor));
 
             this.WhenAny(x => x.SelectedAssignee, x => x.Value)
-                .Where(x => PullRequests != null)
+                .Where(x => PullRequests != null && x != EmptyUser)
                 .Subscribe(a => UpdateFilter(SelectedState, a, SelectedAuthor));
 
             this.WhenAny(x => x.SelectedAuthor, x => x.Value)
-                .Where(x => PullRequests != null)
+                .Where(x => PullRequests != null && x != EmptyUser)
                 .Subscribe(a => UpdateFilter(SelectedState, SelectedAssignee, a));
 
             trackingAuthors = new TrackingCollection<IAccount>(Observable.Empty<IAccount>(),
@@ -73,8 +69,8 @@ public PullRequestListViewModel(IRepositoryHost repositoryHost, ISimpleRepositor
             trackingAuthors.Subscribe();
             trackingAssignees.Subscribe();
 
-            Authors = trackingAuthors.CreateListenerCollection(new List<IAccount> { EmptyUser });
-            Assignees = trackingAssignees.CreateListenerCollection(new List<IAccount> { EmptyUser });
+            Authors = trackingAuthors.CreateListenerCollection(EmptyUser, this.WhenAnyValue(x => x.SelectedAuthor));
+            Assignees = trackingAssignees.CreateListenerCollection(EmptyUser, this.WhenAnyValue(x => x.SelectedAssignee));
 
             PullRequests = new TrackingCollection<IPullRequestModel>();
             pullRequests.Comparer = OrderedComparer<IPullRequestModel>.OrderByDescending(x => x.UpdatedAt).Compare;
@@ -86,7 +82,7 @@ public override void Initialize([AllowNull] ViewWithData data)
         {
             base.Initialize(data);
 
-            PullRequests = repositoryHost.ModelService.GetPullRequests(repository, pullRequests) as TrackingCollection<IPullRequestModel>;
+            PullRequests = repositoryHost.ModelService.GetPullRequests(repository, pullRequests);
             pullRequests.Subscribe(pr =>
             {
                 trackingAssignees.AddItem(pr.Assignee);
@@ -104,12 +100,12 @@ void UpdateFilter(PullRequestState state, [AllowNull]IAccount ass, [AllowNull]IA
                      (aut == null || aut.Equals(pr.Author));
         }
 
-        TrackingCollection<IPullRequestModel> pullRequests;
-        public ObservableCollection<IPullRequestModel> PullRequests
+        ITrackingCollection<IPullRequestModel> pullRequests;
+        public ITrackingCollection<IPullRequestModel> PullRequests
         {
             [return: AllowNull]
             get { return pullRequests; }
-            private set { this.RaiseAndSetIfChanged(ref pullRequests, (TrackingCollection<IPullRequestModel>)value); }
+            private set { this.RaiseAndSetIfChanged(ref pullRequests, value); }
         }
 
         IPullRequestModel selectedPullRequest;

src/GitHub.Exports.Reactive/Collections/TrackingCollection.cs

@@ -16,6 +16,7 @@
 using System.Reactive.Subjects;
 using System.Threading;
 using System.Linq;
+using System.Collections.Specialized;
 
 namespace GitHub.Collections
 {
@@ -47,53 +48,107 @@ public static ObservableCollection<T> CreateListenerCollection<T>(this ITracking
             IList<T> stickieItemsOnTop = null)
             where T : class, ICopyable<T>
         {
-            var col = new ObservableCollection<T>(stickieItemsOnTop ?? Enumerable.Empty<T>());
-            tcol.CollectionChanged += (s, e) =>
+            if (stickieItemsOnTop == null)
             {
-                var offset = 0;
-                if (stickieItemsOnTop != null)
-                {
-                    foreach (var item in stickieItemsOnTop)
-                    {
-                        if (col.Contains(item))
-                            offset++;
-                    }
-                }
+                stickieItemsOnTop = new T[0];
+            }
+
+            var col = new ObservableCollection<T>(stickieItemsOnTop.Concat(tcol));
+            tcol.CollectionChanged += (_, e) => UpdateStickieItems(col, e, stickieItemsOnTop);
+            return col;
+        }
+
+        /// <summary>
+        /// Creates an observable collection that tracks an <see cref="ITrackingCollection{T}"/>
+        /// and adds a sticky item to the top of the collection when a related selection is null.
+        /// </summary>
+        /// <typeparam name="T">The type of items in the collection.</typeparam>
+        /// <param name="tcol">The source tracking collection</param>
+        /// <param name="stickieItemOnTop">The sticky item to add to the top of the collection.</param>
+        /// <param name="selection">
+        /// The current selection. If null or equal to the sticky item then the sticky item will be
+        /// added to the collection.
+        /// </param>
+        /// <returns>An <see cref="ObservableCollection{T}"/>.</returns>
+        public static ObservableCollection<T> CreateListenerCollection<T>(this ITrackingCollection<T> tcol,
+            T stickieItemOnTop,
+            IObservable<T> selection)
+            where T : class, ICopyable<T>
+        {
+            Debug.Assert(stickieItemOnTop != null, "stickieItemOnTop may not be null in CreateListenerCollection");
+            Debug.Assert(selection != null, "selection may not be null in CreateListenerCollection");
+
+            var stickieItems = new[] { stickieItemOnTop };
+            var result = new ObservableCollection<T>(tcol);
+            var hasSelection = false;
+
+            tcol.CollectionChanged += (_, e) =>
+            {
+                UpdateStickieItems(result, e, hasSelection ? stickieItems : null);
+            };
 
-                if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Move)
+            selection.Subscribe(x =>
+            {
+                hasSelection = x != null && !object.Equals(x, stickieItemOnTop);
+                var hasStickie = result.FirstOrDefault() == stickieItemOnTop;
+
+                if (hasSelection && !hasStickie)
                 {
-                    for (int i = 0, oldIdx = e.OldStartingIndex, newIdx = e.NewStartingIndex;
-                        i < e.OldItems.Count; i++, oldIdx++, newIdx++)
-                    {
-                        col.Move(oldIdx + offset, newIdx + offset);
-                    }
+                    result.Insert(0, stickieItemOnTop);
                 }
-                else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
+                else if (hasStickie)
                 {
-                    foreach (T item in e.NewItems)
-                        col.Add(item);
+                    result.Remove(stickieItemOnTop);
                 }
-                else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove)
-                {
-                    foreach (T item in e.OldItems)
-                        col.Remove(item);
-                }
-                else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Replace)
+            });
+
+            return result;
+        }
+
+        static void UpdateStickieItems<T>(
+            ObservableCollection<T> col,
+            NotifyCollectionChangedEventArgs e,
+            IList<T> stickieItemsOnTop)
+        {
+            var offset = 0;
+            if (stickieItemsOnTop != null)
+            {
+                if (object.Equals(col.FirstOrDefault(), stickieItemsOnTop.FirstOrDefault()))
+                    offset = stickieItemsOnTop.Count;
+            }
+
+            if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Move)
+            {
+                for (int i = 0, oldIdx = e.OldStartingIndex, newIdx = e.NewStartingIndex;
+                    i < e.OldItems.Count; i++, oldIdx++, newIdx++)
                 {
-                    for (int i = 0, idx = e.OldStartingIndex; i < e.OldItems.Count; i++, idx++)
-                        col[idx + offset] = (T)e.NewItems[i];
+                    col.Move(oldIdx + offset, newIdx + offset);
                 }
-                else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Reset)
+            }
+            else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
+            {
+                foreach (T item in e.NewItems)
+                    col.Add(item);
+            }
+            else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove)
+            {
+                foreach (T item in e.OldItems)
+                    col.Remove(item);
+            }
+            else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Replace)
+            {
+                for (int i = 0, idx = e.OldStartingIndex; i < e.OldItems.Count; i++, idx++)
+                    col[idx + offset] = (T)e.NewItems[i];
+            }
+            else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Reset)
+            {
+                col.Clear();
+                if (stickieItemsOnTop != null)
                 {
-                    col.Clear();
-                    if (stickieItemsOnTop != null)
-                    {
-                        foreach (var item in stickieItemsOnTop)
-                            col.Add(item);
-                    }
+                    foreach (var item in stickieItemsOnTop)
+                        col.Add(item);
                 }
-            };
-            return col;
+            }
         }
     }
 

src/GitHub.Exports.Reactive/ViewModels/IPullRequestListViewModel.cs

@@ -19,7 +19,7 @@ public override string ToString()
 
     public interface IPullRequestListViewModel : IViewModel
     {
-        ObservableCollection<IPullRequestModel> PullRequests { get; }
+        ITrackingCollection<IPullRequestModel> PullRequests { get; }
         IPullRequestModel SelectedPullRequest { get; }
         ICommand OpenPullRequest { get; }
         IReadOnlyList<PullRequestState> States { get; set; }

src/GitHub.UI/GitHub.UI.csproj

@@ -77,7 +77,6 @@
     <Reference Include="WindowsBase" />
   </ItemGroup>
   <ItemGroup>
-    <Compile Include="Behaviours\AddEmptyItemToList.cs" />
     <Compile Include="Behaviours\ClosePopupAction.cs" />
     <Compile Include="Behaviours\OpenPopupAction.cs" />
     <Compile Include="Controls\Octicons\OcticonPaths.Designer.cs">