diff --git a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/CloneCollection.cs b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/CloneCollection.cs
index 0c830f6..1e3193b 100644
--- a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/CloneCollection.cs
+++ b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/CloneCollection.cs
@@ -49,7 +49,7 @@ public CloneCollection(IEnumerable<T> source)
             }
             else
             {
-                var array = ArrayPool<T>.Shared.Rent(count);
+                var array = ArrayPool<T>.Shared.Rent(16);
 
                 var i = 0;
                 foreach (var item in source)
@@ -75,8 +75,8 @@ static void TryEnsureCapacity(ref T[] array, int index)
             if (array.Length == index)
             {
                 ArrayPool<T>.Shared.Return(array, RuntimeHelpersEx.IsReferenceOrContainsReferences<T>());
+                array = ArrayPool<T>.Shared.Rent(index * 2);
             }
-            array = ArrayPool<T>.Shared.Rent(index * 2);
         }
 
         public void Dispose()
diff --git a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/FreezedView.cs b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/FreezedView.cs
index 710428c..73eeb82 100644
--- a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/FreezedView.cs
+++ b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/FreezedView.cs
@@ -114,7 +114,7 @@ internal sealed class FreezedSortableView<T, TView> : ISortableSynchronizedView<
         public event Action<NotifyCollectionChangedAction> CollectionStateChanged;
         public event NotifyCollectionChangedEventHandler<T> RoutingCollectionChanged;
 
-        public object SyncRoot { get; } = new object();
+        public object SyncRoot { get; } = new();
 
         public FreezedSortableView(IEnumerable<T> source, Func<T, TView> selector)
         {
diff --git a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedView.cs b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedView.cs
index 43b8a98..b8fc49c 100644
--- a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedView.cs
+++ b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedView.cs
@@ -12,7 +12,7 @@ internal class SortedView<T, TKey, TView> : ISynchronizedView<T, TView>
         readonly IObservableCollection<T> source;
         readonly Func<T, TView> transform;
         readonly Func<T, TKey> identitySelector;
-        readonly SortedDictionary<(T Value, TKey Key), (T Value, TView View)> dict;
+        readonly SortedList<(T Value, TKey Key), (T Value, TView View)> list;
 
         ISynchronizedViewFilter<T, TView> filter;
 
@@ -29,13 +29,13 @@ public SortedView(IObservableCollection<T> source, Func<T, TKey> identitySelecto
             this.filter = SynchronizedViewFilter<T, TView>.Null;
             lock (source.SyncRoot)
             {
-                var dict = new SortedDictionary<(T, TKey), (T, TView)>(new Comparer(comparer));
+                var dict = new Dictionary<(T, TKey), (T, TView)>(source.Count);
                 foreach (var v in source)
                 {
                     dict.Add((v, identitySelector(v)), (v, transform(v)));
                 }
 
-                this.dict = dict;
+                this.list = new SortedList<(T Value, TKey Key), (T Value, TView View)>(dict, new Comparer(comparer));
                 this.source.CollectionChanged += SourceCollectionChanged;
             }
         }
@@ -46,7 +46,7 @@ public int Count
             {
                 lock (SyncRoot)
                 {
-                    return dict.Count;
+                    return list.Count;
                 }
             }
         }
@@ -56,7 +56,7 @@ public void AttachFilter(ISynchronizedViewFilter<T, TView> filter)
             lock (SyncRoot)
             {
                 this.filter = filter;
-                foreach (var (_, (value, view)) in dict)
+                foreach (var (_, (value, view)) in list)
                 {
                     filter.InvokeOnAttach(value, view);
                 }
@@ -70,7 +70,7 @@ public void ResetFilter(Action<T, TView> resetAction)
                 this.filter = SynchronizedViewFilter<T, TView>.Null;
                 if (resetAction != null)
                 {
-                    foreach (var (_, (value, view)) in dict)
+                    foreach (var (_, (value, view)) in list)
                     {
                         resetAction(value, view);
                     }
@@ -90,7 +90,7 @@ public INotifyCollectionChangedSynchronizedView<T, TView> WithINotifyCollectionC
         {
             lock (SyncRoot)
             {
-                foreach (var item in dict)
+                foreach (var item in list)
                 {
                     if (filter.IsMatch(item.Value.Value, item.Value.View))
                     {
@@ -114,83 +114,101 @@ private void SourceCollectionChanged(in NotifyCollectionChangedEventArgs<T> e)
                 switch (e.Action)
                 {
                     case NotifyCollectionChangedAction.Add:
+                    {
+                        // Add, Insert
+                        if (e.IsSingleItem)
+                        {
+                            var value = e.NewItem;
+                            var view = transform(value);
+                            var id = identitySelector(value);
+                            list.Add((value, id), (value, view));
+                            var index = list.IndexOfKey((value, id));
+                            filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
+                        }
+                        else
                         {
-                            // Add, Insert
-                            if (e.IsSingleItem)
+                            foreach (var value in e.NewItems)
                             {
-                                var value = e.NewItem;
                                 var view = transform(value);
                                 var id = identitySelector(value);
-                                dict.Add((value, id), (value, view));
-                                filter.InvokeOnAdd(value, view, e);
-                            }
-                            else
-                            {
-                                foreach (var value in e.NewItems)
-                                {
-                                    var view = transform(value);
-                                    var id = identitySelector(value);
-                                    dict.Add((value, id), (value, view));
-                                    filter.InvokeOnAdd(value, view, e);
-                                }
+                                list.Add((value, id), (value, view));
+                                var index = list.IndexOfKey((value, id));
+                                filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
                             }
                         }
+                    }
                         break;
                     case NotifyCollectionChangedAction.Remove:
+                    {
+                        if (e.IsSingleItem)
                         {
-                            if (e.IsSingleItem)
+                            var value = e.OldItem;
+                            var id = identitySelector(value);
+                            var key = (value, id);
+                            if (list.TryGetValue(key, out var v))
                             {
-                                var value = e.OldItem;
-                                var id = identitySelector(value);
-                                dict.Remove((value, id), out var v);
-                                filter.InvokeOnRemove(v.Value, v.View, e);
+                                var index = list.IndexOfKey(key);
+                                list.RemoveAt(index);
+                                filter.InvokeOnRemove(v.Value, v.View, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                             }
-                            else
+                        }
+                        else
+                        {
+                            foreach (var value in e.OldItems)
                             {
-                                foreach (var value in e.OldItems)
+                                var id = identitySelector(value);
+                                var key = (value, id);
+                                if (list.TryGetValue(key, out var v))
                                 {
-                                    var id = identitySelector(value);
-                                    dict.Remove((value, id), out var v);
-                                    filter.InvokeOnRemove(v.Value, v.View, e);
+                                    var index = list.IndexOfKey((value, id));
+                                    list.RemoveAt(index);
+                                    filter.InvokeOnRemove(v.Value, v.View, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                                 }
                             }
                         }
+                    }
                         break;
                     case NotifyCollectionChangedAction.Replace:
                         // ReplaceRange is not supported in all ObservableCollections collections
                         // Replace is remove old item and insert new item.
+                    {
+                        var oldValue = e.OldItem;
+                        var oldKey = (oldValue, identitySelector(oldValue));
+                        if (list.TryGetValue(oldKey, out var o))
                         {
-                            var oldValue = e.OldItem;
-                            dict.Remove((oldValue, identitySelector(oldValue)), out var oldView);
+                            var oldIndex = list.IndexOfKey(oldKey);
+                            list.RemoveAt(oldIndex);
+                            filter.InvokeOnRemove(o, NotifyCollectionChangedEventArgs<T>.Remove(oldValue, oldIndex));
+                        }
 
-                            var value = e.NewItem;
-                            var view = transform(value);
-                            var id = identitySelector(value);
-                            dict.Add((value, id), (value, view));
+                        var value = e.NewItem;
+                        var view = transform(value);
+                        var id = identitySelector(value);
+                        list.Add((value, id), (value, view));
+                        var newIndex = list.IndexOfKey((value, id)); 
 
-                            filter.InvokeOnRemove(oldView, e);
-                            filter.InvokeOnAdd(value, view, e);
-                        }
+                        filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, newIndex));
+                    }
                         break;
                     case NotifyCollectionChangedAction.Move:
+                    {
+                        // Move(index change) does not affect sorted list.
+                        var oldValue = e.OldItem;
+                        if (list.TryGetValue((oldValue, identitySelector(oldValue)), out var view))
                         {
-                            // Move(index change) does not affect sorted list.
-                            var oldValue = e.OldItem;
-                            if (dict.TryGetValue((oldValue, identitySelector(oldValue)), out var view))
-                            {
-                                filter.InvokeOnMove(view, e);
-                            }
+                            filter.InvokeOnMove(view, e);
                         }
+                    }
                         break;
                     case NotifyCollectionChangedAction.Reset:
                         if (!filter.IsNullFilter())
                         {
-                            foreach (var item in dict)
+                            foreach (var item in list)
                             {
                                 filter.InvokeOnRemove(item.Value, e);
                             }
                         }
-                        dict.Clear();
+                        list.Clear();
                         break;
                     default:
                         break;
@@ -222,4 +240,4 @@ public int Compare((T value, TKey id) x, (T value, TKey id) y)
             }
         }
     }
-}
+}
\ No newline at end of file
diff --git a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedViewViewComparer.cs b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedViewViewComparer.cs
index 35b75cd..db41992 100644
--- a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedViewViewComparer.cs
+++ b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Internal/SortedViewViewComparer.cs
@@ -7,13 +7,13 @@
 namespace ObservableCollections.Internal
 {
     internal class SortedViewViewComparer<T, TKey, TView> : ISynchronizedView<T, TView>
-            
+        
     {
         readonly IObservableCollection<T> source;
         readonly Func<T, TView> transform;
         readonly Func<T, TKey> identitySelector;
         readonly Dictionary<TKey, TView> viewMap; // view-map needs to use in remove.
-        readonly SortedDictionary<(TView View, TKey Key), (T Value, TView View)> dict;
+        readonly SortedList<(TView View, TKey Key), (T Value, TView View)> list;
 
         ISynchronizedViewFilter<T, TView> filter;
 
@@ -30,7 +30,7 @@ public SortedViewViewComparer(IObservableCollection<T> source, Func<T, TKey> ide
             this.filter = SynchronizedViewFilter<T, TView>.Null;
             lock (source.SyncRoot)
             {
-                var dict = new SortedDictionary<(TView, TKey), (T, TView)>(new Comparer(comparer));
+                var dict = new Dictionary<(TView, TKey), (T, TView)>(source.Count);
                 this.viewMap = new Dictionary<TKey, TView>();
                 foreach (var value in source)
                 {
@@ -39,7 +39,7 @@ public SortedViewViewComparer(IObservableCollection<T> source, Func<T, TKey> ide
                     dict.Add((view, id), (value, view));
                     viewMap.Add(id, view);
                 }
-                this.dict = dict;
+                this.list = new SortedList<(TView View, TKey Key), (T Value, TView View)>(dict, new Comparer(comparer));
                 this.source.CollectionChanged += SourceCollectionChanged;
             }
         }
@@ -50,7 +50,7 @@ public int Count
             {
                 lock (SyncRoot)
                 {
-                    return dict.Count;
+                    return list.Count;
                 }
             }
         }
@@ -60,7 +60,7 @@ public void AttachFilter(ISynchronizedViewFilter<T, TView> filter)
             lock (SyncRoot)
             {
                 this.filter = filter;
-                foreach (var (_, (value, view)) in dict)
+                foreach (var (_, (value, view)) in list)
                 {
                     filter.InvokeOnAttach(value, view);
                 }
@@ -74,7 +74,7 @@ public void ResetFilter(Action<T, TView> resetAction)
                 this.filter = SynchronizedViewFilter<T, TView>.Null;
                 if (resetAction != null)
                 {
-                    foreach (var (_, (value, view)) in dict)
+                    foreach (var (_, (value, view)) in list)
                     {
                         resetAction(value, view);
                     }
@@ -95,7 +95,7 @@ public INotifyCollectionChangedSynchronizedView<T, TView> WithINotifyCollectionC
 
             lock (SyncRoot)
             {
-                foreach (var item in dict)
+                foreach (var item in list)
                 {
                     if (filter.IsMatch(item.Value.Value, item.Value.View))
                     {
@@ -119,96 +119,114 @@ private void SourceCollectionChanged(in NotifyCollectionChangedEventArgs<T> e)
                 switch (e.Action)
                 {
                     case NotifyCollectionChangedAction.Add:
+                    {
+                        // Add, Insert
+                        if (e.IsSingleItem)
                         {
-                            // Add, Insert
-                            if (e.IsSingleItem)
+                            var value = e.NewItem;
+                            var view = transform(value);
+                            var id = identitySelector(value);
+                            list.Add((view, id), (value, view));
+                            viewMap.Add(id, view);
+                            var index = list.IndexOfKey((view, id));
+                            filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
+                        }
+                        else
+                        {
+                            foreach (var value in e.NewItems)
                             {
-                                var value = e.NewItem;
                                 var view = transform(value);
                                 var id = identitySelector(value);
-                                dict.Add((view, id), (value, view));
+                                list.Add((view, id), (value, view));
                                 viewMap.Add(id, view);
-                                filter.InvokeOnAdd(value, view, e);
-                            }
-                            else
-                            {
-                                foreach (var value in e.NewItems)
-                                {
-                                    var view = transform(value);
-                                    var id = identitySelector(value);
-                                    dict.Add((view, id), (value, view));
-                                    viewMap.Add(id, view);
-                                    filter.InvokeOnAdd(value, view, e);
-                                }
+                                var index = list.IndexOfKey((view, id));                                            
+                                filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
                             }
                         }
                         break;
+                    }
                     case NotifyCollectionChangedAction.Remove:
+                    {
+                        if (e.IsSingleItem)
                         {
-                            if (e.IsSingleItem)
+                            var value = e.OldItem;
+                            var id = identitySelector(value);
+                            if (viewMap.Remove(id, out var view))
                             {
-                                var value = e.OldItem;
-                                var id = identitySelector(value);
-                                if (viewMap.Remove(id, out var view))
+                                var key = (view, id);
+                                if (list.TryGetValue(key, out var v))
                                 {
-                                    dict.Remove((view, id), out var v);
-                                    filter.InvokeOnRemove(v, e);
+                                    var index = list.IndexOfKey(key);
+                                    list.RemoveAt(index);
+                                    filter.InvokeOnRemove(v, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                                 }
                             }
-                            else
+                        }
+                        else
+                        {
+                            foreach (var value in e.OldItems)
                             {
-                                foreach (var value in e.OldItems)
+                                var id = identitySelector(value);
+                                if (viewMap.Remove(id, out var view))
                                 {
-                                    var id = identitySelector(value);
-                                    if (viewMap.Remove(id, out var view))
+                                    var key = (view, id);
+                                    if (list.TryGetValue(key, out var v))
                                     {
-                                        dict.Remove((view, id), out var v);
-                                        filter.InvokeOnRemove(v, e);
+                                        var index = list.IndexOfKey((view, id));
+                                        list.RemoveAt(index);
+                                        filter.InvokeOnRemove(v, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                                     }
                                 }
                             }
                         }
                         break;
+                    }
                     case NotifyCollectionChangedAction.Replace:
                         // Replace is remove old item and insert new item.
+                    {
+                        var oldValue = e.OldItem;
+                        var oldId = identitySelector(oldValue);
+                        if (viewMap.Remove(oldId, out var oldView))
                         {
-                            var oldValue = e.OldItem;
-                            var oldKey = identitySelector(oldValue);
-                            if (viewMap.Remove(oldKey, out var oldView))
+                            var oldKey = (oldView, oldId);
+                            if (list.TryGetValue(oldKey, out var v))
                             {
-                                dict.Remove((oldView, oldKey));
-                                filter.InvokeOnRemove(oldValue, oldView, e);
+                                var oldIndex = list.IndexOfKey(oldKey);
+                                list.RemoveAt(oldIndex);
+                                filter.InvokeOnRemove(oldValue, oldView, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, oldIndex));
                             }
+                        }
 
-                            var value = e.NewItem;
-                            var view = transform(value);
-                            var id = identitySelector(value);
-                            dict.Add((view, id), (value, view));
-                            viewMap.Add(id, view);
+                        var value = e.NewItem;
+                        var view = transform(value);
+                        var id = identitySelector(value);
+                        list.Add((view, id), (value, view));
+                        viewMap.Add(id, view);
 
-                            filter.InvokeOnAdd(value, view, e);
-                        }
+                        var index = list.IndexOfKey((view, id));
+                        filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
                         break;
+                    }
                     case NotifyCollectionChangedAction.Move:
                         // Move(index change) does not affect soreted dict.
+                    {
+                        var value = e.OldItem;
+                        var key = identitySelector(value);
+                        if (viewMap.TryGetValue(key, out var view))
                         {
-                            var value = e.OldItem;
-                            var key = identitySelector(value);
-                            if (viewMap.TryGetValue(key, out var view))
-                            {
-                                filter.InvokeOnMove(value, view, e);
-                            }
+                            filter.InvokeOnMove(value, view, e);
                         }
                         break;
+                    }
                     case NotifyCollectionChangedAction.Reset:
                         if (!filter.IsNullFilter())
                         {
-                            foreach (var item in dict)
+                            foreach (var item in list)
                             {
                                 filter.InvokeOnRemove(item.Value, e);
                             }
                         }
-                        dict.Clear();
+                        list.Clear();
                         viewMap.Clear();
                         break;
                     default:
diff --git a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Shims/Nullables.cs b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Shims/Nullables.cs
index eba1209..9b745a3 100644
--- a/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Shims/Nullables.cs
+++ b/src/ObservableCollections.Unity/Assets/Plugins/ObservableCollections/Runtime/Shims/Nullables.cs
@@ -2,7 +2,7 @@
 using System.Collections.Generic;
 using System.Text;
 
-#if (NETSTANDARD2_0 || NET_STANDARD_2_0 || NET_4_6) && !UNITY_2021_1_OR_NEWER
+#if NETSTANDARD2_0 || NET_STANDARD_2_0 || NET_4_6
 
 namespace System.Diagnostics.CodeAnalysis
 {
diff --git a/src/ObservableCollections/Internal/FreezedView.cs b/src/ObservableCollections/Internal/FreezedView.cs
index 95f7748..371ee87 100644
--- a/src/ObservableCollections/Internal/FreezedView.cs
+++ b/src/ObservableCollections/Internal/FreezedView.cs
@@ -114,7 +114,7 @@ internal sealed class FreezedSortableView<T, TView> : ISortableSynchronizedView<
         public event Action<NotifyCollectionChangedAction>? CollectionStateChanged;
         public event NotifyCollectionChangedEventHandler<T>? RoutingCollectionChanged;
 
-        public object SyncRoot { get; } = new object();
+        public object SyncRoot { get; } = new();
 
         public FreezedSortableView(IEnumerable<T> source, Func<T, TView> selector)
         {
diff --git a/src/ObservableCollections/Internal/SortedView.cs b/src/ObservableCollections/Internal/SortedView.cs
index 0411985..a43f128 100644
--- a/src/ObservableCollections/Internal/SortedView.cs
+++ b/src/ObservableCollections/Internal/SortedView.cs
@@ -12,7 +12,7 @@ internal class SortedView<T, TKey, TView> : ISynchronizedView<T, TView>
         readonly IObservableCollection<T> source;
         readonly Func<T, TView> transform;
         readonly Func<T, TKey> identitySelector;
-        readonly SortedDictionary<(T Value, TKey Key), (T Value, TView View)> dict;
+        readonly SortedList<(T Value, TKey Key), (T Value, TView View)> list;
 
         ISynchronizedViewFilter<T, TView> filter;
 
@@ -29,13 +29,13 @@ public SortedView(IObservableCollection<T> source, Func<T, TKey> identitySelecto
             this.filter = SynchronizedViewFilter<T, TView>.Null;
             lock (source.SyncRoot)
             {
-                var dict = new SortedDictionary<(T, TKey), (T, TView)>(new Comparer(comparer));
+                var dict = new Dictionary<(T, TKey), (T, TView)>(source.Count);
                 foreach (var v in source)
                 {
                     dict.Add((v, identitySelector(v)), (v, transform(v)));
                 }
 
-                this.dict = dict;
+                this.list = new SortedList<(T Value, TKey Key), (T Value, TView View)>(dict, new Comparer(comparer));
                 this.source.CollectionChanged += SourceCollectionChanged;
             }
         }
@@ -46,7 +46,7 @@ public int Count
             {
                 lock (SyncRoot)
                 {
-                    return dict.Count;
+                    return list.Count;
                 }
             }
         }
@@ -56,7 +56,7 @@ public void AttachFilter(ISynchronizedViewFilter<T, TView> filter)
             lock (SyncRoot)
             {
                 this.filter = filter;
-                foreach (var (_, (value, view)) in dict)
+                foreach (var (_, (value, view)) in list)
                 {
                     filter.InvokeOnAttach(value, view);
                 }
@@ -70,7 +70,7 @@ public void ResetFilter(Action<T, TView>? resetAction)
                 this.filter = SynchronizedViewFilter<T, TView>.Null;
                 if (resetAction != null)
                 {
-                    foreach (var (_, (value, view)) in dict)
+                    foreach (var (_, (value, view)) in list)
                     {
                         resetAction(value, view);
                     }
@@ -90,7 +90,7 @@ public INotifyCollectionChangedSynchronizedView<T, TView> WithINotifyCollectionC
         {
             lock (SyncRoot)
             {
-                foreach (var item in dict)
+                foreach (var item in list)
                 {
                     if (filter.IsMatch(item.Value.Value, item.Value.View))
                     {
@@ -114,83 +114,101 @@ private void SourceCollectionChanged(in NotifyCollectionChangedEventArgs<T> e)
                 switch (e.Action)
                 {
                     case NotifyCollectionChangedAction.Add:
+                    {
+                        // Add, Insert
+                        if (e.IsSingleItem)
+                        {
+                            var value = e.NewItem;
+                            var view = transform(value);
+                            var id = identitySelector(value);
+                            list.Add((value, id), (value, view));
+                            var index = list.IndexOfKey((value, id));
+                            filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
+                        }
+                        else
                         {
-                            // Add, Insert
-                            if (e.IsSingleItem)
+                            foreach (var value in e.NewItems)
                             {
-                                var value = e.NewItem;
                                 var view = transform(value);
                                 var id = identitySelector(value);
-                                dict.Add((value, id), (value, view));
-                                filter.InvokeOnAdd(value, view, e);
-                            }
-                            else
-                            {
-                                foreach (var value in e.NewItems)
-                                {
-                                    var view = transform(value);
-                                    var id = identitySelector(value);
-                                    dict.Add((value, id), (value, view));
-                                    filter.InvokeOnAdd(value, view, e);
-                                }
+                                list.Add((value, id), (value, view));
+                                var index = list.IndexOfKey((value, id));
+                                filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
                             }
                         }
+                    }
                         break;
                     case NotifyCollectionChangedAction.Remove:
+                    {
+                        if (e.IsSingleItem)
                         {
-                            if (e.IsSingleItem)
+                            var value = e.OldItem;
+                            var id = identitySelector(value);
+                            var key = (value, id);
+                            if (list.TryGetValue(key, out var v))
                             {
-                                var value = e.OldItem;
-                                var id = identitySelector(value);
-                                dict.Remove((value, id), out var v);
-                                filter.InvokeOnRemove(v.Value, v.View, e);
+                                var index = list.IndexOfKey(key);
+                                list.RemoveAt(index);
+                                filter.InvokeOnRemove(v.Value, v.View, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                             }
-                            else
+                        }
+                        else
+                        {
+                            foreach (var value in e.OldItems)
                             {
-                                foreach (var value in e.OldItems)
+                                var id = identitySelector(value);
+                                var key = (value, id);
+                                if (list.TryGetValue(key, out var v))
                                 {
-                                    var id = identitySelector(value);
-                                    dict.Remove((value, id), out var v);
-                                    filter.InvokeOnRemove(v.Value, v.View, e);
+                                    var index = list.IndexOfKey((value, id));
+                                    list.RemoveAt(index);
+                                    filter.InvokeOnRemove(v.Value, v.View, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                                 }
                             }
                         }
+                    }
                         break;
                     case NotifyCollectionChangedAction.Replace:
                         // ReplaceRange is not supported in all ObservableCollections collections
                         // Replace is remove old item and insert new item.
+                    {
+                        var oldValue = e.OldItem;
+                        var oldKey = (oldValue, identitySelector(oldValue));
+                        if (list.TryGetValue(oldKey, out var o))
                         {
-                            var oldValue = e.OldItem;
-                            dict.Remove((oldValue, identitySelector(oldValue)), out var oldView);
+                            var oldIndex = list.IndexOfKey(oldKey);
+                            list.RemoveAt(oldIndex);
+                            filter.InvokeOnRemove(o, NotifyCollectionChangedEventArgs<T>.Remove(oldValue, oldIndex));
+                        }
 
-                            var value = e.NewItem;
-                            var view = transform(value);
-                            var id = identitySelector(value);
-                            dict.Add((value, id), (value, view));
+                        var value = e.NewItem;
+                        var view = transform(value);
+                        var id = identitySelector(value);
+                        list.Add((value, id), (value, view));
+                        var newIndex = list.IndexOfKey((value, id)); 
 
-                            filter.InvokeOnRemove(oldView, e);
-                            filter.InvokeOnAdd(value, view, e);
-                        }
+                        filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, newIndex));
+                    }
                         break;
                     case NotifyCollectionChangedAction.Move:
+                    {
+                        // Move(index change) does not affect sorted list.
+                        var oldValue = e.OldItem;
+                        if (list.TryGetValue((oldValue, identitySelector(oldValue)), out var view))
                         {
-                            // Move(index change) does not affect sorted list.
-                            var oldValue = e.OldItem;
-                            if (dict.TryGetValue((oldValue, identitySelector(oldValue)), out var view))
-                            {
-                                filter.InvokeOnMove(view, e);
-                            }
+                            filter.InvokeOnMove(view, e);
                         }
+                    }
                         break;
                     case NotifyCollectionChangedAction.Reset:
                         if (!filter.IsNullFilter())
                         {
-                            foreach (var item in dict)
+                            foreach (var item in list)
                             {
                                 filter.InvokeOnRemove(item.Value, e);
                             }
                         }
-                        dict.Clear();
+                        list.Clear();
                         break;
                     default:
                         break;
@@ -222,4 +240,4 @@ public int Compare((T value, TKey id) x, (T value, TKey id) y)
             }
         }
     }
-}
+}
\ No newline at end of file
diff --git a/src/ObservableCollections/Internal/SortedViewViewComparer.cs b/src/ObservableCollections/Internal/SortedViewViewComparer.cs
index 383c2eb..e8dc8a1 100644
--- a/src/ObservableCollections/Internal/SortedViewViewComparer.cs
+++ b/src/ObservableCollections/Internal/SortedViewViewComparer.cs
@@ -7,13 +7,13 @@
 namespace ObservableCollections.Internal
 {
     internal class SortedViewViewComparer<T, TKey, TView> : ISynchronizedView<T, TView>
-            where TKey : notnull
+        where TKey : notnull
     {
         readonly IObservableCollection<T> source;
         readonly Func<T, TView> transform;
         readonly Func<T, TKey> identitySelector;
         readonly Dictionary<TKey, TView> viewMap; // view-map needs to use in remove.
-        readonly SortedDictionary<(TView View, TKey Key), (T Value, TView View)> dict;
+        readonly SortedList<(TView View, TKey Key), (T Value, TView View)> list;
 
         ISynchronizedViewFilter<T, TView> filter;
 
@@ -30,7 +30,7 @@ public SortedViewViewComparer(IObservableCollection<T> source, Func<T, TKey> ide
             this.filter = SynchronizedViewFilter<T, TView>.Null;
             lock (source.SyncRoot)
             {
-                var dict = new SortedDictionary<(TView, TKey), (T, TView)>(new Comparer(comparer));
+                var dict = new Dictionary<(TView, TKey), (T, TView)>(source.Count);
                 this.viewMap = new Dictionary<TKey, TView>();
                 foreach (var value in source)
                 {
@@ -39,7 +39,7 @@ public SortedViewViewComparer(IObservableCollection<T> source, Func<T, TKey> ide
                     dict.Add((view, id), (value, view));
                     viewMap.Add(id, view);
                 }
-                this.dict = dict;
+                this.list = new SortedList<(TView View, TKey Key), (T Value, TView View)>(dict, new Comparer(comparer));
                 this.source.CollectionChanged += SourceCollectionChanged;
             }
         }
@@ -50,7 +50,7 @@ public int Count
             {
                 lock (SyncRoot)
                 {
-                    return dict.Count;
+                    return list.Count;
                 }
             }
         }
@@ -60,7 +60,7 @@ public void AttachFilter(ISynchronizedViewFilter<T, TView> filter)
             lock (SyncRoot)
             {
                 this.filter = filter;
-                foreach (var (_, (value, view)) in dict)
+                foreach (var (_, (value, view)) in list)
                 {
                     filter.InvokeOnAttach(value, view);
                 }
@@ -74,7 +74,7 @@ public void ResetFilter(Action<T, TView>? resetAction)
                 this.filter = SynchronizedViewFilter<T, TView>.Null;
                 if (resetAction != null)
                 {
-                    foreach (var (_, (value, view)) in dict)
+                    foreach (var (_, (value, view)) in list)
                     {
                         resetAction(value, view);
                     }
@@ -95,7 +95,7 @@ public INotifyCollectionChangedSynchronizedView<T, TView> WithINotifyCollectionC
 
             lock (SyncRoot)
             {
-                foreach (var item in dict)
+                foreach (var item in list)
                 {
                     if (filter.IsMatch(item.Value.Value, item.Value.View))
                     {
@@ -119,96 +119,114 @@ private void SourceCollectionChanged(in NotifyCollectionChangedEventArgs<T> e)
                 switch (e.Action)
                 {
                     case NotifyCollectionChangedAction.Add:
+                    {
+                        // Add, Insert
+                        if (e.IsSingleItem)
                         {
-                            // Add, Insert
-                            if (e.IsSingleItem)
+                            var value = e.NewItem;
+                            var view = transform(value);
+                            var id = identitySelector(value);
+                            list.Add((view, id), (value, view));
+                            viewMap.Add(id, view);
+                            var index = list.IndexOfKey((view, id));
+                            filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
+                        }
+                        else
+                        {
+                            foreach (var value in e.NewItems)
                             {
-                                var value = e.NewItem;
                                 var view = transform(value);
                                 var id = identitySelector(value);
-                                dict.Add((view, id), (value, view));
+                                list.Add((view, id), (value, view));
                                 viewMap.Add(id, view);
-                                filter.InvokeOnAdd(value, view, e);
-                            }
-                            else
-                            {
-                                foreach (var value in e.NewItems)
-                                {
-                                    var view = transform(value);
-                                    var id = identitySelector(value);
-                                    dict.Add((view, id), (value, view));
-                                    viewMap.Add(id, view);
-                                    filter.InvokeOnAdd(value, view, e);
-                                }
+                                var index = list.IndexOfKey((view, id));                                            
+                                filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
                             }
                         }
                         break;
+                    }
                     case NotifyCollectionChangedAction.Remove:
+                    {
+                        if (e.IsSingleItem)
                         {
-                            if (e.IsSingleItem)
+                            var value = e.OldItem;
+                            var id = identitySelector(value);
+                            if (viewMap.Remove(id, out var view))
                             {
-                                var value = e.OldItem;
-                                var id = identitySelector(value);
-                                if (viewMap.Remove(id, out var view))
+                                var key = (view, id);
+                                if (list.TryGetValue(key, out var v))
                                 {
-                                    dict.Remove((view, id), out var v);
-                                    filter.InvokeOnRemove(v, e);
+                                    var index = list.IndexOfKey(key);
+                                    list.RemoveAt(index);
+                                    filter.InvokeOnRemove(v, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                                 }
                             }
-                            else
+                        }
+                        else
+                        {
+                            foreach (var value in e.OldItems)
                             {
-                                foreach (var value in e.OldItems)
+                                var id = identitySelector(value);
+                                if (viewMap.Remove(id, out var view))
                                 {
-                                    var id = identitySelector(value);
-                                    if (viewMap.Remove(id, out var view))
+                                    var key = (view, id);
+                                    if (list.TryGetValue(key, out var v))
                                     {
-                                        dict.Remove((view, id), out var v);
-                                        filter.InvokeOnRemove(v, e);
+                                        var index = list.IndexOfKey((view, id));
+                                        list.RemoveAt(index);
+                                        filter.InvokeOnRemove(v, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, index));
                                     }
                                 }
                             }
                         }
                         break;
+                    }
                     case NotifyCollectionChangedAction.Replace:
                         // Replace is remove old item and insert new item.
+                    {
+                        var oldValue = e.OldItem;
+                        var oldId = identitySelector(oldValue);
+                        if (viewMap.Remove(oldId, out var oldView))
                         {
-                            var oldValue = e.OldItem;
-                            var oldKey = identitySelector(oldValue);
-                            if (viewMap.Remove(oldKey, out var oldView))
+                            var oldKey = (oldView, oldId);
+                            if (list.TryGetValue(oldKey, out var v))
                             {
-                                dict.Remove((oldView, oldKey));
-                                filter.InvokeOnRemove(oldValue, oldView, e);
+                                var oldIndex = list.IndexOfKey(oldKey);
+                                list.RemoveAt(oldIndex);
+                                filter.InvokeOnRemove(oldValue, oldView, NotifyCollectionChangedEventArgs<T>.Remove(v.Value, oldIndex));
                             }
+                        }
 
-                            var value = e.NewItem;
-                            var view = transform(value);
-                            var id = identitySelector(value);
-                            dict.Add((view, id), (value, view));
-                            viewMap.Add(id, view);
+                        var value = e.NewItem;
+                        var view = transform(value);
+                        var id = identitySelector(value);
+                        list.Add((view, id), (value, view));
+                        viewMap.Add(id, view);
 
-                            filter.InvokeOnAdd(value, view, e);
-                        }
+                        var index = list.IndexOfKey((view, id));
+                        filter.InvokeOnAdd(value, view, NotifyCollectionChangedEventArgs<T>.Add(value, index));
                         break;
+                    }
                     case NotifyCollectionChangedAction.Move:
                         // Move(index change) does not affect soreted dict.
+                    {
+                        var value = e.OldItem;
+                        var key = identitySelector(value);
+                        if (viewMap.TryGetValue(key, out var view))
                         {
-                            var value = e.OldItem;
-                            var key = identitySelector(value);
-                            if (viewMap.TryGetValue(key, out var view))
-                            {
-                                filter.InvokeOnMove(value, view, e);
-                            }
+                            filter.InvokeOnMove(value, view, e);
                         }
                         break;
+                    }
                     case NotifyCollectionChangedAction.Reset:
                         if (!filter.IsNullFilter())
                         {
-                            foreach (var item in dict)
+                            foreach (var item in list)
                             {
                                 filter.InvokeOnRemove(item.Value, e);
                             }
                         }
-                        dict.Clear();
+                        list.Clear();
                         viewMap.Clear();
                         break;
                     default:
diff --git a/tests/ObservableCollections.Tests/SortedViewTest.cs b/tests/ObservableCollections.Tests/SortedViewTest.cs
new file mode 100644
index 0000000..4b22bec
--- /dev/null
+++ b/tests/ObservableCollections.Tests/SortedViewTest.cs
@@ -0,0 +1,69 @@
+using System.Collections.Generic;
+
+namespace ObservableCollections.Tests;
+
+public class SortedViewTest
+{
+    [Fact]
+    public void Sort()
+    {
+        var list = new ObservableList<int>();
+        var sortedView = list.CreateSortedView(
+            x => x,
+            x => new ViewContainer<int>(x),
+            Comparer<int>.Default);
+
+        list.Add(10);
+        list.Add(50);
+        list.Add(30);
+        list.Add(20);
+        list.Add(40);
+
+        using var e = sortedView.GetEnumerator();
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(10);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(20);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(30);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(40);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(50);
+        e.MoveNext().Should().BeFalse();
+    }
+    
+    [Fact]
+    public void ObserveIndex()
+    {
+        var list = new ObservableList<int>();
+        var sortedView = list.CreateSortedView(
+            x => x,
+            x => new ViewContainer<int>(x),
+            Comparer<int>.Default);
+
+        var filter = new TestFilter<int>((value, view) => value % 2 == 0);
+        list.Add(50);
+        list.Add(10);
+        
+        sortedView.AttachFilter(filter);
+        
+        list.Add(20);
+        filter.CalledOnCollectionChanged[0].changedKind.Should().Be(ChangedKind.Add);
+        filter.CalledOnCollectionChanged[0].value.Should().Be(20);
+        filter.CalledOnCollectionChanged[0].index.Should().Be(1);
+
+        list.Remove(20);
+        filter.CalledOnCollectionChanged[1].changedKind.Should().Be(ChangedKind.Remove);
+        filter.CalledOnCollectionChanged[1].value.Should().Be(20);
+        filter.CalledOnCollectionChanged[1].oldIndex.Should().Be(1);
+
+        list[1] = 999; // from 10(at 0 in original) to 999
+        filter.CalledOnCollectionChanged[2].changedKind.Should().Be(ChangedKind.Remove);
+        filter.CalledOnCollectionChanged[2].value.Should().Be(10);
+        filter.CalledOnCollectionChanged[2].oldIndex.Should().Be(0);
+        filter.CalledOnCollectionChanged[3].changedKind.Should().Be(ChangedKind.Add);
+        filter.CalledOnCollectionChanged[3].value.Should().Be(999);
+        filter.CalledOnCollectionChanged[3].index.Should().Be(1);
+    }
+}
\ No newline at end of file
diff --git a/tests/ObservableCollections.Tests/SortedViewViewComparerTest.cs b/tests/ObservableCollections.Tests/SortedViewViewComparerTest.cs
new file mode 100644
index 0000000..ee6dcf3
--- /dev/null
+++ b/tests/ObservableCollections.Tests/SortedViewViewComparerTest.cs
@@ -0,0 +1,69 @@
+using System.Collections.Generic;
+
+namespace ObservableCollections.Tests;
+
+public class SortedViewViewComparerTest
+{
+    [Fact]
+    public void Sort()
+    {
+        var list = new ObservableList<int>();
+        var sortedView = list.CreateSortedView(
+            x => x,
+            x => new ViewContainer<int>(x),
+            Comparer<ViewContainer<int>>.Default);
+
+        list.Add(10);
+        list.Add(50);
+        list.Add(30);
+        list.Add(20);
+        list.Add(40);
+
+        using var e = sortedView.GetEnumerator();
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(10);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(20);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(30);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(40);
+        e.MoveNext().Should().BeTrue();
+        e.Current.Value.Should().Be(50);
+        e.MoveNext().Should().BeFalse();
+    }
+    
+    [Fact]
+    public void ObserveIndex()
+    {
+        var list = new ObservableList<int>();
+        var sortedView = list.CreateSortedView(
+            x => x,
+            x => new ViewContainer<int>(x),
+            Comparer<ViewContainer<int>>.Default);
+
+        var filter = new TestFilter<int>((value, view) => value % 2 == 0);
+        list.Add(50);
+        list.Add(10);
+        
+        sortedView.AttachFilter(filter);
+        
+        list.Add(20);
+        filter.CalledOnCollectionChanged[0].changedKind.Should().Be(ChangedKind.Add);
+        filter.CalledOnCollectionChanged[0].value.Should().Be(20);
+        filter.CalledOnCollectionChanged[0].index.Should().Be(1);
+
+        list.Remove(20);
+        filter.CalledOnCollectionChanged[1].changedKind.Should().Be(ChangedKind.Remove);
+        filter.CalledOnCollectionChanged[1].value.Should().Be(20);
+        filter.CalledOnCollectionChanged[1].oldIndex.Should().Be(1);
+
+        list[1] = 999; // from 10(at 0 in original) to 999
+        filter.CalledOnCollectionChanged[2].changedKind.Should().Be(ChangedKind.Remove);
+        filter.CalledOnCollectionChanged[2].value.Should().Be(10);
+        filter.CalledOnCollectionChanged[2].oldIndex.Should().Be(0);
+        filter.CalledOnCollectionChanged[3].changedKind.Should().Be(ChangedKind.Add);
+        filter.CalledOnCollectionChanged[3].value.Should().Be(999);
+        filter.CalledOnCollectionChanged[3].index.Should().Be(1);
+    }
+}
\ No newline at end of file
diff --git a/tests/ObservableCollections.Tests/ViewContainer.cs b/tests/ObservableCollections.Tests/ViewContainer.cs
index 947d689..256941b 100644
--- a/tests/ObservableCollections.Tests/ViewContainer.cs
+++ b/tests/ObservableCollections.Tests/ViewContainer.cs
@@ -35,7 +35,7 @@ public class TestFilter<T> : ISynchronizedViewFilter<T, ViewContainer<T>>
         readonly Func<T, ViewContainer<T>, bool> filter;
         public List<(T, ViewContainer<T>)> CalledWhenTrue = new();
         public List<(T, ViewContainer<T>)> CalledWhenFalse = new();
-        public List<(ChangedKind changedKind, T value, ViewContainer<T> view)> CalledOnCollectionChanged = new();
+        public List<(ChangedKind changedKind, T value, ViewContainer<T> view, int index, int oldIndex)> CalledOnCollectionChanged = new();
 
         public TestFilter(Func<T, ViewContainer<T>, bool> filter)
         {
@@ -56,7 +56,7 @@ public bool IsMatch(T value, ViewContainer<T> view)
 
         public void OnCollectionChanged(ChangedKind changedKind, T value, ViewContainer<T> view, in NotifyCollectionChangedEventArgs<T> eventArgs)
         {
-            CalledOnCollectionChanged.Add((changedKind, value, view));
+            CalledOnCollectionChanged.Add((changedKind, value, view, eventArgs.NewStartingIndex, eventArgs.OldStartingIndex));
         }
 
         public void WhenTrue(T value, ViewContainer<T> view)