optimize for ObservableList

sandbox/WpfApp/MainWindow.xaml

@@ -20,6 +20,12 @@
     <StackPanel>
         <ListBox ItemsSource="{Binding ItemsView}" />
         <Button Content="Add" Command="{Binding AddCommand}" />
+        <Button Content="Insert" Command="{Binding InsertAtRandomCommand}" />
+        <Button Content="Remove" Command="{Binding RemoveAtRandomCommand}" />
         <Button Content="Clear" Command="{Binding ClearCommand}" />
+        <Button Content="Reverse" Command="{Binding ReverseCommand}" />
+        <Button Content="Sort" Command="{Binding SortCommand}" />
+        <Button Content="AttachFilter" Command="{Binding AttachFilterCommand}" />
+        <Button Content="ResetFilter" Command="{Binding ResetFilterCommand}" />
     </StackPanel>
 </Window>

sandbox/WpfApp/MainWindow.xaml.cs

@@ -76,19 +76,26 @@ namespace WpfApp
         private ObservableList<int> observableList { get; } = new ObservableList<int>();
         public INotifyCollectionChangedSynchronizedView<int> ItemsView { get; }
         public ReactiveCommand<Unit> AddCommand { get; } = new ReactiveCommand<Unit>();
+        public ReactiveCommand<Unit> InsertAtRandomCommand { get; } = new ReactiveCommand<Unit>();
+        public ReactiveCommand<Unit> RemoveAtRandomCommand { get; } = new ReactiveCommand<Unit>();
         public ReactiveCommand<Unit> ClearCommand { get; } = new ReactiveCommand<Unit>();
+        public ReactiveCommand<Unit> ReverseCommand { get; } = new ReactiveCommand<Unit>();
+        public ReactiveCommand<Unit> SortCommand { get; } = new ReactiveCommand<Unit>();
+        public ReactiveCommand<Unit> AttachFilterCommand { get; } = new ReactiveCommand<Unit>();
+        public ReactiveCommand<Unit> ResetFilterCommand { get; } = new ReactiveCommand<Unit>();
 
         public ViewModel()
         {
             observableList.Add(1);
             observableList.Add(2);
 
-            ItemsView = observableList.CreateView(x => x).ToNotifyCollectionChanged(SynchronizationContextCollectionEventDispatcher.Current);
+            var view = observableList.CreateView(x => x);
+            ItemsView = view.ToNotifyCollectionChanged(SynchronizationContextCollectionEventDispatcher.Current);
 
 
-            // ItemsView = observableList.CreateView(x => x).ToNotifyCollectionChanged();
+            // check for optimize list
+            // ItemsView = observableList.ToNotifyCollectionChanged(SynchronizationContextCollectionEventDispatcher.Current);
 
-            // BindingOperations.EnableCollectionSynchronization(ItemsView, new object());
 
             AddCommand.Subscribe(_ =>
             {
@@ -98,12 +105,43 @@ namespace WpfApp
                 });
             });
 
-            // var iii = 10;
+            InsertAtRandomCommand.Subscribe(_ =>
+            {
+                var from = Random.Shared.Next(0, view.Count);
+                observableList.Insert(from, Random.Shared.Next());
+            });
+
+            RemoveAtRandomCommand.Subscribe(_ =>
+            {
+                var from = Random.Shared.Next(0, view.Count);
+                observableList.RemoveAt(from);
+            });
+
             ClearCommand.Subscribe(_ =>
             {
-                // observableList.Add(iii++);
                 observableList.Clear();
             });
+
+
+            ReverseCommand.Subscribe(_ =>
+            {
+                observableList.Reverse();
+            });
+
+            SortCommand.Subscribe(_ =>
+            {
+                observableList.Sort();
+            });
+
+            AttachFilterCommand.Subscribe(_ =>
+            {
+                view.AttachFilter(x => x % 2 == 0);
+            });
+
+            ResetFilterCommand.Subscribe(_ =>
+            {
+                view.ResetFilter();
+            });
         }
     }
 

src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs

@@ -50,7 +50,7 @@ public static class ObservableCollectionR3Extensions
         return new ObservableCollectionClear<T>(source, cancellationToken);
     }
 
-    public static Observable<Unit> ObserveReverse<T>(this IObservableCollection<T> source, CancellationToken cancellationToken = default)
+    public static Observable<(int Index, int Count))> ObserveReverse<T>(this IObservableCollection<T> source, CancellationToken cancellationToken = default)
     {
         return new ObservableCollectionReverse<T>(source, cancellationToken);
     }
@@ -251,24 +251,24 @@ sealed class ObservableCollectionClear<T>(IObservableCollection<T> collection, C
     }
 }
 
-sealed class ObservableCollectionReverse<T>(IObservableCollection<T> collection, CancellationToken cancellationToken) : Observable<Unit>
+sealed class ObservableCollectionReverse<T>(IObservableCollection<T> collection, CancellationToken cancellationToken) : Observable<(int Index, int Count)>
 {
-    protected override IDisposable SubscribeCore(Observer<Unit> observer)
+    protected override IDisposable SubscribeCore(Observer<(int Index, int Count)> observer)
     {
         return new _ObservableCollectionReverse(collection, observer, cancellationToken);
     }
 
     sealed class _ObservableCollectionReverse(
         IObservableCollection<T> collection,
-        Observer<Unit> observer,
+        Observer<(int Index, int Count)> observer,
         CancellationToken cancellationToken)
-        : ObservableCollectionObserverBase<T, Unit>(collection, observer, cancellationToken)
+        : ObservableCollectionObserverBase<T, (int Index, int Count)>(collection, observer, cancellationToken)
     {
         protected override void Handler(in NotifyCollectionChangedEventArgs<T> eventArgs)
         {
             if (eventArgs.Action == NotifyCollectionChangedAction.Reset && eventArgs.SortOperation.IsReverse)
             {
-                observer.OnNext(Unit.Default);
+                observer.OnNext((eventArgs.SortOperation.Index, eventArgs.SortOperation.Count));
             }
         }
     }

src/ObservableCollections/AlternateIndexList.cs

@@ -40,7 +40,7 @@ public class AlternateIndexList<T> : IEnumerable<T>
 
     public int Count => list.Count;
 
-    public void Insert(int alternateIndex, T value)
+    public int Insert(int alternateIndex, T value)
     {
         var index = list.BinarySearch(alternateIndex);
         if (index < 0)
@@ -49,9 +49,10 @@ public class AlternateIndexList<T> : IEnumerable<T>
         }
         list.Insert(index, new(alternateIndex, value));
         UpdateAlternateIndex(index + 1, 1);
+        return index;
     }
 
-    public void InsertRange(int startingAlternateIndex, IEnumerable<T> values)
+    public int InsertRange(int startingAlternateIndex, IEnumerable<T> values)
     {
         var index = list.BinarySearch(startingAlternateIndex);
         if (index < 0)
@@ -62,9 +63,10 @@ public class AlternateIndexList<T> : IEnumerable<T>
         using var iter = new InsertIterator(startingAlternateIndex, values);
         list.InsertRange(index, iter);
         UpdateAlternateIndex(index + iter.ConsumedCount, iter.ConsumedCount);
+        return index;
     }
 
-    public void Remove(T value)
+    public int Remove(T value)
     {
         var index = list.FindIndex(x => EqualityComparer<T>.Default.Equals(x.Value, value));
         if (index != -1)
@@ -72,9 +74,10 @@ public class AlternateIndexList<T> : IEnumerable<T>
             list.RemoveAt(index);
             UpdateAlternateIndex(index, -1);
         }
+        return index;
     }
 
-    public void RemoveAt(int alternateIndex)
+    public int RemoveAt(int alternateIndex)
     {
         var index = list.BinarySearch(alternateIndex);
         if (index != -1)
@@ -82,9 +85,10 @@ public class AlternateIndexList<T> : IEnumerable<T>
             list.RemoveAt(index);
             UpdateAlternateIndex(index, -1);
         }
+        return index;
     }
 
-    public void RemoveRange(int alternateIndex, int count)
+    public int RemoveRange(int alternateIndex, int count)
     {
         var index = list.BinarySearch(alternateIndex);
         if (index < 0)
@@ -94,6 +98,7 @@ public class AlternateIndexList<T> : IEnumerable<T>
 
         list.RemoveRange(index, count);
         UpdateAlternateIndex(index, -count);
+        return index;
     }
 
     public bool TryGetAtAlternateIndex(int alternateIndex, [MaybeNullWhen(true)] out T value)
@@ -108,23 +113,23 @@ public class AlternateIndexList<T> : IEnumerable<T>
         return true;
     }
 
-    public bool TrySetAtAlternateIndex(int alternateIndex, T value)
+    public bool TrySetAtAlternateIndex(int alternateIndex, T value, out int setIndex)
     {
-        var index = list.BinarySearch(alternateIndex);
+        setIndex = list.BinarySearch(alternateIndex);
-        if (index < 0)
+        if (setIndex < 0)
         {
             return false;
         }
-        CollectionsMarshal.AsSpan(list)[index].Value = value;
+        CollectionsMarshal.AsSpan(list)[setIndex].Value = value;
         return true;
     }
 
-    public bool TryReplaceByValue(T searchValue, T replaceValue)
+    public bool TryReplaceByValue(T searchValue, T replaceValue, out int replacedIndex)
     {
-        var index = list.FindIndex(x => EqualityComparer<T>.Default.Equals(x.Value, searchValue));
+        replacedIndex = list.FindIndex(x => EqualityComparer<T>.Default.Equals(x.Value, searchValue));
-        if (index != -1)
+        if (replacedIndex != -1)
         {
-            CollectionsMarshal.AsSpan(list)[index].Value = replaceValue;
+            CollectionsMarshal.AsSpan(list)[replacedIndex].Value = replaceValue;
             return true;
         }
         return false;

src/ObservableCollections/NotifyCollectionChangedEventArgs.cs

@@ -16,8 +16,6 @@ namespace ObservableCollections
 
         public bool IsReverse => Comparer == ReverseSentinel.Instance;
         public bool IsNull => Comparer == null;
-
-        [MemberNotNullWhen(true, nameof(Comparer))]
         public bool IsSort => !IsNull && !IsReverse;
 
         public SortOperation(int index, int count, IComparer<T>? comparer)
@@ -53,7 +51,7 @@ namespace ObservableCollections
 
             public int Compare(T? x, T? y)
             {
-                throw new NotImplementedException();
+                return Comparer<T>.Default.Compare(x!, y!);
             }
         }
     }

src/ObservableCollections/ObservableDictionary.Views.cs

@@ -110,7 +110,7 @@ namespace ObservableCollections
 
             public ISynchronizedViewList<TView> ToViewList()
             {
-                return new SynchronizedViewList<KeyValuePair<TKey, TValue>, TView>(this);
+                return new FiltableSynchronizedViewList<KeyValuePair<TKey, TValue>, TView>(this);
             }
 
             public INotifyCollectionChangedSynchronizedView<TView> ToNotifyCollectionChanged()

src/ObservableCollections/ObservableHashSet.Views.cs

@@ -105,7 +105,7 @@ namespace ObservableCollections
 
             public ISynchronizedViewList<TView> ToViewList()
             {
-                return new SynchronizedViewList<T, TView>(this);
+                return new FiltableSynchronizedViewList<T, TView>(this);
             }
 
             public INotifyCollectionChangedSynchronizedView<TView> ToNotifyCollectionChanged()

src/ObservableCollections/ObservableList.Views.cs

@@ -16,17 +16,30 @@ namespace ObservableCollections
 
         public ISynchronizedViewList<T> ToViewList()
         {
-            return CreateView(static x => x).ToViewList();
+            // NOTE: for more optimize, no need to create View.
+            return ToViewList(static x => x);
+        }
+
+        public ISynchronizedViewList<TView> ToViewList<TView>(Func<T, TView> transform)
+        {
+            // Optimized for non filtered
+            return new NonFilteredSynchronizedViewList<T, TView>(CreateView(transform));
         }
 
         public INotifyCollectionChangedSynchronizedView<T> ToNotifyCollectionChanged()
         {
-            return CreateView(static x => x).ToNotifyCollectionChanged();
+            return ToNotifyCollectionChanged(null);
         }
 
         public INotifyCollectionChangedSynchronizedView<T> ToNotifyCollectionChanged(ICollectionEventDispatcher? collectionEventDispatcher)
         {
-            return CreateView(static x => x).ToNotifyCollectionChanged(collectionEventDispatcher);
+            return ToNotifyCollectionChanged(static x => x, collectionEventDispatcher);
+        }
+
+        public INotifyCollectionChangedSynchronizedView<TView> ToNotifyCollectionChanged<TView>(Func<T, TView> transform, ICollectionEventDispatcher? collectionEventDispatcher)
+        {
+            // Optimized for non filtered
+            return new NonFilteredNotifyCollectionChangedSynchronizedView<T, TView>(CreateView(transform), collectionEventDispatcher);
         }
 
         internal sealed class View<TView> : ISynchronizedView<T, TView>
@@ -123,7 +136,7 @@ namespace ObservableCollections
 
             public ISynchronizedViewList<TView> ToViewList()
             {
-                return new SynchronizedViewList<T, TView>(this);
+                return new FiltableSynchronizedViewList<T, TView>(this);
             }
 
             public INotifyCollectionChangedSynchronizedView<TView> ToNotifyCollectionChanged()
@@ -315,7 +328,7 @@ namespace ObservableCollections
                 }
             }
 
-            internal sealed class IgnoreViewComparer : IComparer<(T, TView)>
+            sealed class IgnoreViewComparer : IComparer<(T, TView)>
             {
                 readonly IComparer<T> comparer;
 

src/ObservableCollections/ObservableList.cs

@@ -291,7 +291,7 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                list.Sort();
+                list.Sort(comparer);
                 CollectionChanged?.Invoke(NotifyCollectionChangedEventArgs<T>.Sort(0, list.Count, comparer));
             }
         }
@@ -300,7 +300,7 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                list.Sort();
+                list.Sort(index, count, comparer);
                 CollectionChanged?.Invoke(NotifyCollectionChangedEventArgs<T>.Sort(index, count, comparer));
             }
         }
@@ -309,7 +309,7 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                list.Sort();
+                list.Reverse();
                 CollectionChanged?.Invoke(NotifyCollectionChangedEventArgs<T>.Reverse(0, list.Count));
             }
         }
@@ -318,7 +318,7 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                list.Sort();
+                list.Reverse(index, count);
                 CollectionChanged?.Invoke(NotifyCollectionChangedEventArgs<T>.Reverse(index, count));
             }
         }

src/ObservableCollections/ObservableQueue.Views.cs

@@ -105,7 +105,7 @@ namespace ObservableCollections
 
             public ISynchronizedViewList<TView> ToViewList()
             {
-                return new SynchronizedViewList<T, TView>(this);
+                return new FiltableSynchronizedViewList<T, TView>(this);
             }
 
             public INotifyCollectionChangedSynchronizedView<TView> ToNotifyCollectionChanged()

src/ObservableCollections/ObservableRingBuffer.Views.cs

@@ -107,7 +107,7 @@ namespace ObservableCollections
 
             public ISynchronizedViewList<TView> ToViewList()
             {
-                return new SynchronizedViewList<T, TView>(this);
+                return new FiltableSynchronizedViewList<T, TView>(this);
             }
 
             public INotifyCollectionChangedSynchronizedView<TView> ToNotifyCollectionChanged()

src/ObservableCollections/ObservableStack.Views.cs

@@ -104,7 +104,7 @@ namespace ObservableCollections
 
             public ISynchronizedViewList<TView> ToViewList()
             {
-                return new SynchronizedViewList<T, TView>(this);
+                return new FiltableSynchronizedViewList<T, TView>(this);
             }
 
             public INotifyCollectionChangedSynchronizedView<TView> ToNotifyCollectionChanged()

src/ObservableCollections/SynchronizedViewChangedEventArgs.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Specialized;
 using System.Data;
+using System.Runtime.CompilerServices;
 
 namespace ObservableCollections
 {
@@ -28,6 +29,55 @@ namespace ObservableCollections
         public readonly int NewStartingIndex = newStartingIndex;
         public readonly int OldStartingIndex = oldStartingIndex;
         public readonly SortOperation<T> SortOperation = sortOperation;
+
+        public SynchronizedViewChangedEventArgs<T, TView> WithNewStartingIndex(int newStartingIndex)
+        {
+            // MEMO: struct copy and replace only newStartingIndex memory maybe fast.
+            return new SynchronizedViewChangedEventArgs<T, TView>(
+                action,
+                IsSingleItem,
+                newItem: NewItem,
+                oldItem: OldItem,
+                newValues: NewValues,
+                newViews: NewViews,
+                oldValues: OldValues,
+                oldViews: OldViews,
+                newStartingIndex: newStartingIndex, // replace
+                oldStartingIndex: OldStartingIndex,
+                sortOperation: SortOperation);
+        }
+
+        public SynchronizedViewChangedEventArgs<T, TView> WithOldStartingIndex(int oldStartingIndex)
+        {
+            return new SynchronizedViewChangedEventArgs<T, TView>(
+                action,
+                IsSingleItem,
+                newItem: NewItem,
+                oldItem: OldItem,
+                newValues: NewValues,
+                newViews: NewViews,
+                oldValues: OldValues,
+                oldViews: OldViews,
+                newStartingIndex: NewStartingIndex,
+                oldStartingIndex: oldStartingIndex, // replace
+                sortOperation: SortOperation);
+        }
+
+        public SynchronizedViewChangedEventArgs<T, TView> WithNewAndOldStartingIndex(int newStartingIndex, int oldStartingIndex)
+        {
+            return new SynchronizedViewChangedEventArgs<T, TView>(
+                action,
+                IsSingleItem,
+                newItem: NewItem,
+                oldItem: OldItem,
+                newValues: NewValues,
+                newViews: NewViews,
+                oldValues: OldValues,
+                oldViews: OldViews,
+                newStartingIndex: newStartingIndex, // replace
+                oldStartingIndex: oldStartingIndex, // replace
+                sortOperation: SortOperation);
+        }
     }
 
     public static class SynchronizedViewExtensions

src/ObservableCollections/SynchronizedViewList.cs

@@ -5,17 +5,18 @@ using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Linq;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 namespace ObservableCollections;
 
-internal class SynchronizedViewList<T, TView> : ISynchronizedViewList<TView>
+internal class FiltableSynchronizedViewList<T, TView> : ISynchronizedViewList<TView>
 {
     readonly ISynchronizedView<T, TView> parent;
     protected readonly AlternateIndexList<TView> listView;
     protected readonly object gate = new object();
 
-    public SynchronizedViewList(ISynchronizedView<T, TView> parent)
+    public FiltableSynchronizedViewList(ISynchronizedView<T, TView> parent)
     {
         this.parent = parent;
         lock (parent.SyncRoot)
@@ -60,24 +61,29 @@ internal class SynchronizedViewList<T, TView> : ISynchronizedViewList<TView>
                 case NotifyCollectionChangedAction.Add: // Add or Insert
                     if (e.IsSingleItem)
                     {
-                        listView.Insert(e.NewStartingIndex, e.NewItem.View);
+                        var index = listView.Insert(e.NewStartingIndex, e.NewItem.View);
+                        OnCollectionChanged(e.WithNewStartingIndex(index));
+                        return;
                     }
                     else
                     {
                         using var array = new CloneCollection<TView>(e.NewViews);
-                        listView.InsertRange(e.NewStartingIndex, array.AsEnumerable());
+                        var index = listView.InsertRange(e.NewStartingIndex, array.AsEnumerable());
+                        OnCollectionChanged(e.WithNewStartingIndex(index));
+                        return;
                     }
-                    break;
                 case NotifyCollectionChangedAction.Remove: // Remove
+                    {
+                        int index = e.OldStartingIndex;
                         if (e.IsSingleItem)
                         {
                             if (e.OldStartingIndex == -1) // can't gurantee correct remove if index is not provided
                             {
-                            listView.Remove(e.OldItem.View);
+                                index = listView.Remove(e.OldItem.View);
                             }
                             else
                             {
-                            listView.RemoveAt(e.OldStartingIndex);
+                                index = listView.RemoveAt(e.OldStartingIndex);
                             }
                         }
                         else
@@ -87,34 +93,53 @@ internal class SynchronizedViewList<T, TView> : ISynchronizedViewList<TView>
                                 foreach (var view in e.OldViews) // index is unknown, can't do batching
                                 {
                                     listView.Remove(view);
+                                    OnCollectionChanged(e.WithOldStartingIndex(index));
                                 }
+                                return;
                             }
                             else
                             {
-                            listView.RemoveRange(e.OldStartingIndex, e.OldViews.Length);
+                                index = listView.RemoveRange(e.OldStartingIndex, e.OldViews.Length);
                             }
                         }
-                    break;
+                        OnCollectionChanged(e.WithOldStartingIndex(index));
+                        return;
+                    }
                 case NotifyCollectionChangedAction.Replace: // Indexer
                     if (e.NewStartingIndex == -1)
                     {
-                        listView.TryReplaceByValue(e.OldItem.View, e.NewItem.View);
+                        if (listView.TryReplaceByValue(e.OldItem.View, e.NewItem.View, out var replacedIndex))
+                        {
+                            OnCollectionChanged(e.WithNewAndOldStartingIndex(replacedIndex, replacedIndex));
+                            return;
                         }
                         else
                         {
-                        listView.TrySetAtAlternateIndex(e.NewStartingIndex, e.NewItem.View);
+                            return;
+                        }
+                    }
+                    else
+                    {
+                        if (listView.TrySetAtAlternateIndex(e.NewStartingIndex, e.NewItem.View, out var setIndex))
+                        {
+                            OnCollectionChanged(e.WithNewAndOldStartingIndex(setIndex, setIndex));
+                            return;
+                        }
+                        else
+                        {
+                            return;
+                        }
                     }
-
-                    break;
                 case NotifyCollectionChangedAction.Move: //Remove and Insert
                     if (e.NewStartingIndex == -1)
                     {
-                        // do nothing
+                        return; // do nothing
                     }
                     else
                     {
-                        listView.RemoveAt(e.OldStartingIndex);
+                        var oldIndex = listView.RemoveAt(e.OldStartingIndex);
-                        listView.Insert(e.NewStartingIndex, e.NewItem.View);
+                        var newIndex = listView.Insert(e.NewStartingIndex, e.NewItem.View);
+                        OnCollectionChanged(e.WithNewAndOldStartingIndex(newStartingIndex: newIndex, oldStartingIndex: oldIndex));
                     }
                     break;
                 case NotifyCollectionChangedAction.Reset: // Clear or drastic changes
@@ -176,8 +201,225 @@ internal class SynchronizedViewList<T, TView> : ISynchronizedViewList<TView>
     }
 }
 
+internal class NonFilteredSynchronizedViewList<T, TView> : ISynchronizedViewList<TView>
+{
+    readonly ISynchronizedView<T, TView> parent;
+    protected readonly List<TView> listView; // no filter can be faster
+    protected readonly object gate = new object();
+
+    public NonFilteredSynchronizedViewList(ISynchronizedView<T, TView> parent)
+    {
+        this.parent = parent;
+        lock (parent.SyncRoot)
+        {
+            listView = parent.ToList(); // iterate filtered
+            parent.ViewChanged += Parent_ViewChanged;
+        }
+    }
+
+    private void Parent_ViewChanged(in SynchronizedViewChangedEventArgs<T, TView> e)
+    {
+        // event is called inside parent lock
+        lock (gate)
+        {
+            switch (e.Action)
+            {
+                case NotifyCollectionChangedAction.Add: // Add or Insert
+                    if (e.IsSingleItem)
+                    {
+                        listView.Insert(e.NewStartingIndex, e.NewItem.View);
+                    }
+                    else
+                    {
+#if NET8_0_OR_GREATER
+                        listView.InsertRange(e.NewStartingIndex, e.NewViews);
+#else
+                        using var array = new CloneCollection<TView>(e.NewViews);
+                        listView.InsertRange(e.NewStartingIndex, array.AsEnumerable());
+#endif
+                    }
+                    break;
+                case NotifyCollectionChangedAction.Remove: // Remove
+                    {
+                        if (e.IsSingleItem)
+                        {
+                            if (e.OldStartingIndex == -1) // can't gurantee correct remove if index is not provided
+                            {
+                                var index = listView.IndexOf(e.OldItem.View);
+                                listView.RemoveAt(index);
+                                OnCollectionChanged(e.WithOldStartingIndex(index));
+                                return;
+                            }
+                            else
+                            {
+                                listView.RemoveAt(e.OldStartingIndex);
+                            }
+                        }
+                        else
+                        {
+                            if (e.OldStartingIndex == -1)
+                            {
+                                foreach (var view in e.OldViews) // index is unknown, can't do batching
+                                {
+                                    var index = listView.IndexOf(view);
+                                    listView.RemoveAt(index);
+                                    OnCollectionChanged(e.WithOldStartingIndex(index));
+                                }
+                                return;
+                            }
+                            else
+                            {
+                                listView.RemoveRange(e.OldStartingIndex, e.OldViews.Length);
+                            }
+                        }
+                        break;
+                    }
+                case NotifyCollectionChangedAction.Replace: // Indexer
+                    if (e.NewStartingIndex == -1)
+                    {
+                        var index = listView.IndexOf(e.OldItem.View);
+                        if (index != -1)
+                        {
+                            listView[index] = e.NewItem.View;
+                            OnCollectionChanged(e.WithNewAndOldStartingIndex(index, index));
+                            return;
+                        }
+                        else
+                        {
+                            return;
+                        }
+                    }
+                    else
+                    {
+                        listView[e.NewStartingIndex] = e.NewItem.View;
+                    }
+                    break;
+                case NotifyCollectionChangedAction.Move: //Remove and Insert
+                    if (e.NewStartingIndex == -1)
+                    {
+                        return; // do nothing
+                    }
+                    else
+                    {
+                        listView.RemoveAt(e.OldStartingIndex);
+                        listView.Insert(e.NewStartingIndex, e.NewItem.View);
+                    }
+                    break;
+                case NotifyCollectionChangedAction.Reset: // Clear or drastic changes
+                    if (e.SortOperation.IsNull)
+                    {
+                        listView.Clear();
+                        foreach (var item in parent.Unfiltered) // refresh
+                        {
+                            listView.Add(item.View);
+                        }
+                    }
+                    else if (e.SortOperation.IsReverse)
+                    {
+                        listView.Reverse(e.SortOperation.Index, e.SortOperation.Count);
+                    }
+                    else
+                    {
+
+
+
+#if NET6_0_OR_GREATER
+#pragma warning disable CS0436
+                        if (parent is ObservableList<T>.View<TView> observableListView && typeof(T) == typeof(TView))
+                        {
+                            var comparer = new ViewComparer(e.SortOperation.Comparer ?? Comparer<T>.Default);
+                            var viewSpan = CollectionsMarshal.AsSpan(listView).Slice(e.SortOperation.Index, e.SortOperation.Count);
+                            viewSpan.Sort(comparer);
+                        }
+                        else
+#pragma warning restore CS0436
+#endif
+                        {
+                            // can not get source Span, do Clear and Refresh
+                            listView.Clear();
+                            foreach (var item in parent.Unfiltered)
+                            {
+                                listView.Add(item.View);
+                            }
+                        }
+                    }
+                    break;
+                default:
+                    break;
+            }
+
+            OnCollectionChanged(e);
+        }
+    }
+
+    sealed class ViewComparer : IComparer<TView>
+    {
+        readonly IComparer<T> comparer;
+
+        public ViewComparer(IComparer<T> comparer)
+        {
+            this.comparer = comparer;
+        }
+
+        public int Compare(TView? x, TView? y)
+        {
+            var t1 = Unsafe.As<TView, T>(ref x!);
+            var t2 = Unsafe.As<TView, T>(ref y!);
+            return comparer.Compare(t1, t2);
+        }
+    }
+
+    protected virtual void OnCollectionChanged(in SynchronizedViewChangedEventArgs<T, TView> args)
+    {
+    }
+
+    public TView this[int index]
+    {
+        get
+        {
+            lock (gate)
+            {
+                return listView[index];
+            }
+        }
+    }
+
+    public int Count
+    {
+        get
+        {
+            lock (gate)
+            {
+                return listView.Count;
+            }
+        }
+    }
+
+    public IEnumerator<TView> GetEnumerator()
+    {
+        lock (gate)
+        {
+            foreach (var item in listView)
+            {
+                yield return item;
+            }
+        }
+    }
+
+    IEnumerator IEnumerable.GetEnumerator()
+    {
+        return listView.GetEnumerator();
+    }
+
+    public void Dispose()
+    {
+        parent.ViewChanged -= Parent_ViewChanged;
+        parent.Dispose(); // Dispose parent
+    }
+}
+
 internal class NotifyCollectionChangedSynchronizedView<T, TView> :
-    SynchronizedViewList<T, TView>,
+    FiltableSynchronizedViewList<T, TView>,
     INotifyCollectionChangedSynchronizedView<TView>,
     IList<TView>, IList
 {
@@ -420,3 +662,248 @@ internal class NotifyCollectionChangedSynchronizedView<T, TView> :
         throw new NotSupportedException();
     }
 }
+
+internal class NonFilteredNotifyCollectionChangedSynchronizedView<T, TView> :
+    NonFilteredSynchronizedViewList<T, TView>,
+    INotifyCollectionChangedSynchronizedView<TView>,
+    IList<TView>, IList
+{
+    static readonly PropertyChangedEventArgs CountPropertyChangedEventArgs = new("Count");
+    static readonly Action<NotifyCollectionChangedEventArgs> raiseChangedEventInvoke = RaiseChangedEvent;
+
+    readonly ICollectionEventDispatcher eventDispatcher;
+
+    public event NotifyCollectionChangedEventHandler? CollectionChanged;
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    public NonFilteredNotifyCollectionChangedSynchronizedView(ISynchronizedView<T, TView> parent, ICollectionEventDispatcher? eventDispatcher)
+        : base(parent)
+    {
+        this.eventDispatcher = eventDispatcher ?? InlineCollectionEventDispatcher.Instance;
+    }
+
+    protected override void OnCollectionChanged(in SynchronizedViewChangedEventArgs<T, TView> args)
+    {
+        if (CollectionChanged == null && PropertyChanged == null) return;
+
+        switch (args.Action)
+        {
+            case NotifyCollectionChangedAction.Add:
+                if (args.IsSingleItem)
+                {
+                    eventDispatcher.Post(new CollectionEventDispatcherEventArgs(NotifyCollectionChangedAction.Add, args.NewItem.View, args.NewStartingIndex)
+                    {
+                        Collection = this,
+                        Invoker = raiseChangedEventInvoke,
+                        IsInvokeCollectionChanged = true,
+                        IsInvokePropertyChanged = true
+                    });
+                }
+                else
+                {
+                    eventDispatcher.Post(new CollectionEventDispatcherEventArgs(NotifyCollectionChangedAction.Add, args.NewViews.ToArray(), args.NewStartingIndex)
+                    {
+                        Collection = this,
+                        Invoker = raiseChangedEventInvoke,
+                        IsInvokeCollectionChanged = true,
+                        IsInvokePropertyChanged = true
+                    });
+                }
+                break;
+            case NotifyCollectionChangedAction.Remove:
+                if (args.IsSingleItem)
+                {
+                    eventDispatcher.Post(new CollectionEventDispatcherEventArgs(NotifyCollectionChangedAction.Remove, args.OldItem.View, args.OldStartingIndex)
+                    {
+                        Collection = this,
+                        Invoker = raiseChangedEventInvoke,
+                        IsInvokeCollectionChanged = true,
+                        IsInvokePropertyChanged = true
+                    });
+                }
+                else
+                {
+                    eventDispatcher.Post(new CollectionEventDispatcherEventArgs(NotifyCollectionChangedAction.Remove, args.OldViews.ToArray(), args.OldStartingIndex)
+                    {
+                        Collection = this,
+                        Invoker = raiseChangedEventInvoke,
+                        IsInvokeCollectionChanged = true,
+                        IsInvokePropertyChanged = true
+                    });
+                }
+                break;
+            case NotifyCollectionChangedAction.Reset:
+                eventDispatcher.Post(new CollectionEventDispatcherEventArgs(NotifyCollectionChangedAction.Reset)
+                {
+                    Collection = this,
+                    Invoker = raiseChangedEventInvoke,
+                    IsInvokeCollectionChanged = true,
+                    IsInvokePropertyChanged = true
+                });
+                break;
+            case NotifyCollectionChangedAction.Replace:
+                eventDispatcher.Post(new CollectionEventDispatcherEventArgs(NotifyCollectionChangedAction.Replace, args.NewItem.View, args.OldItem.View, args.NewStartingIndex)
+                {
+                    Collection = this,
+                    Invoker = raiseChangedEventInvoke,
+                    IsInvokeCollectionChanged = true,
+                    IsInvokePropertyChanged = false
+                });
+                break;
+            case NotifyCollectionChangedAction.Move:
+                eventDispatcher.Post(new CollectionEventDispatcherEventArgs(NotifyCollectionChangedAction.Move, args.NewItem.View, args.NewStartingIndex, args.OldStartingIndex)
+                {
+                    Collection = this,
+                    Invoker = raiseChangedEventInvoke,
+                    IsInvokeCollectionChanged = true,
+                    IsInvokePropertyChanged = false
+                });
+                break;
+        }
+    }
+
+    static void RaiseChangedEvent(NotifyCollectionChangedEventArgs e)
+    {
+        var e2 = (CollectionEventDispatcherEventArgs)e;
+        var self = (NonFilteredNotifyCollectionChangedSynchronizedView<T, TView>)e2.Collection;
+
+        if (e2.IsInvokeCollectionChanged)
+        {
+            self.CollectionChanged?.Invoke(self, e);
+        }
+        if (e2.IsInvokePropertyChanged)
+        {
+            self.PropertyChanged?.Invoke(self, CountPropertyChangedEventArgs);
+        }
+    }
+
+    // IList<T>, IList implementation
+
+    TView IList<TView>.this[int index]
+    {
+        get => ((IReadOnlyList<TView>)this)[index];
+        set => throw new NotSupportedException();
+    }
+
+    object? IList.this[int index]
+    {
+        get
+        {
+            return this[index];
+        }
+        set => throw new NotSupportedException();
+    }
+
+    static bool IsCompatibleObject(object? value)
+    {
+        return value is TView || value == null && default(TView) == null;
+    }
+
+    public bool IsReadOnly => true;
+
+    public bool IsFixedSize => false;
+
+    public bool IsSynchronized => true;
+
+    public object SyncRoot => gate;
+
+    public void Add(TView item)
+    {
+        throw new NotSupportedException();
+    }
+
+    public int Add(object? value)
+    {
+        throw new NotImplementedException();
+    }
+
+    public void Clear()
+    {
+        throw new NotSupportedException();
+    }
+
+    public bool Contains(TView item)
+    {
+        lock (gate)
+        {
+            foreach (var listItem in listView)
+            {
+                if (EqualityComparer<TView>.Default.Equals(listItem, item))
+                {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    public bool Contains(object? value)
+    {
+        if (IsCompatibleObject(value))
+        {
+            return Contains((TView)value!);
+        }
+        return false;
+    }
+
+    public void CopyTo(TView[] array, int arrayIndex)
+    {
+        throw new NotSupportedException();
+    }
+
+    public void CopyTo(Array array, int index)
+    {
+        throw new NotImplementedException();
+    }
+
+    public int IndexOf(TView item)
+    {
+        lock (gate)
+        {
+            var index = 0;
+            foreach (var listItem in listView)
+            {
+                if (EqualityComparer<TView>.Default.Equals(listItem, item))
+                {
+                    return index;
+                }
+                index++;
+            }
+        }
+        return -1;
+    }
+
+    public int IndexOf(object? item)
+    {
+        if (IsCompatibleObject(item))
+        {
+            return IndexOf((TView)item!);
+        }
+        return -1;
+    }
+
+    public void Insert(int index, TView item)
+    {
+        throw new NotSupportedException();
+    }
+
+    public void Insert(int index, object? value)
+    {
+        throw new NotImplementedException();
+    }
+
+    public bool Remove(TView item)
+    {
+        throw new NotSupportedException();
+    }
+
+    public void Remove(object? value)
+    {
+        throw new NotImplementedException();
+    }
+
+    public void RemoveAt(int index)
+    {
+        throw new NotSupportedException();
+    }
+}