diff --git a/src/ObservableCollections.R3/ObservableCollectionR3Extensions.View.cs b/src/ObservableCollections.R3/ObservableCollectionR3Extensions.View.cs
new file mode 100644
index 0000000..3bc84d2
--- /dev/null
+++ b/src/ObservableCollections.R3/ObservableCollectionR3Extensions.View.cs
@@ -0,0 +1,509 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Specialized;
+using System.Diagnostics.Tracing;
+using System.Runtime.InteropServices;
+using System.Threading;
+using R3;
+
+namespace ObservableCollections;
+
+[StructLayout(LayoutKind.Auto)]
+public readonly record struct ViewChangedEvent<T, TView>
+{
+    public readonly NotifyCollectionChangedAction Action;
+    public readonly (T Value, TView View) NewItem;
+    public readonly (T Value, TView View) OldItem;
+    public readonly int NewStartingIndex;
+    public readonly int OldStartingIndex;
+    public readonly SortOperation<T> SortOperation;
+
+    public ViewChangedEvent(NotifyCollectionChangedAction action, (T, TView) newItem, (T, TView) oldItem, int newStartingIndex, int oldStartingIndex, SortOperation<T> sortOperation)
+    {
+        Action = action;
+        NewItem = newItem;
+        OldItem = oldItem;
+        NewStartingIndex = newStartingIndex;
+        OldStartingIndex = oldStartingIndex;
+        SortOperation = sortOperation;
+    }
+}
+
+[StructLayout(LayoutKind.Auto)]
+public readonly record struct RejectedViewChangedEvent
+{
+    public readonly RejectedViewChangedAction Action;
+    public readonly int NewIndex;
+    public readonly int OldIndex;
+
+    public RejectedViewChangedEvent(RejectedViewChangedAction action, int newIndex, int oldIndex)
+    {
+        Action = action;
+        NewIndex = newIndex;
+        OldIndex = oldIndex;
+    }
+}
+
+public static partial class ObservableCollectionR3Extensions
+{
+    public static Observable<RejectedViewChangedEvent> ObserveRejected<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewRejected<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<ViewChangedEvent<T, TView>> ObserveChanged<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewChanged<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<CollectionAddEvent<(T Value, TView View)>> ObserveAdd<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewAdd<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<CollectionRemoveEvent<(T Value, TView View)>> ObserveRemove<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewRemove<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<CollectionReplaceEvent<(T Value, TView View)>> ObserveReplace<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewReplace<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<CollectionMoveEvent<(T Value, TView View)>> ObserveMove<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewMove<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<CollectionResetEvent<T>> ObserveReset<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewReset<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<Unit> ObserveClear<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewClear<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<(int Index, int Count)> ObserveReverse<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewReverse<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<(int Index, int Count, IComparer<T>? Comparer)> ObserveSort<T, TView>(this ISynchronizedView<T, TView> source, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewSort<T, TView>(source, cancellationToken);
+    }
+
+    public static Observable<int> ObserveCountChanged<T, TView>(this ISynchronizedView<T, TView> source, bool notifyCurrentCount = false, CancellationToken cancellationToken = default)
+    {
+        return new SynchronizedViewCountChanged<T, TView>(source, notifyCurrentCount, cancellationToken);
+    }
+}
+
+sealed class SynchronizedViewChanged<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<ViewChangedEvent<T, TView>>
+{
+    protected override IDisposable SubscribeCore(Observer<ViewChangedEvent<T, TView>> observer)
+    {
+        return new _SynchronizedViewChanged(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewChanged(
+        ISynchronizedView<T, TView> source,
+        Observer<ViewChangedEvent<T, TView>> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, ViewChangedEvent<T, TView>>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.IsSingleItem)
+            {
+                var newArgs = new ViewChangedEvent<T, TView>(
+                    eventArgs.Action,
+                    eventArgs.NewItem,
+                    eventArgs.OldItem,
+                    eventArgs.NewStartingIndex,
+                    eventArgs.OldStartingIndex,
+                    eventArgs.SortOperation);
+
+                observer.OnNext(newArgs);
+            }
+            else
+            {
+                if (eventArgs.Action == NotifyCollectionChangedAction.Add)
+                {
+                    var index = eventArgs.NewStartingIndex;
+                    for (int i = 0; i < eventArgs.NewValues.Length; i++)
+                    {
+                        var newItem = (eventArgs.NewValues[i], eventArgs.NewViews[i]);
+                        var newArgs = new ViewChangedEvent<T, TView>(
+                            eventArgs.Action,
+                            newItem,
+                            default,
+                            index++,
+                            eventArgs.OldStartingIndex,
+                            eventArgs.SortOperation);
+
+                        observer.OnNext(newArgs);
+                    }
+                }
+                else if (eventArgs.Action == NotifyCollectionChangedAction.Remove)
+                {
+
+                    for (int i = 0; i < eventArgs.OldValues.Length; i++)
+                    {
+                        var oldItem = (eventArgs.OldValues[i], eventArgs.OldViews[i]);
+                        var newArgs = new ViewChangedEvent<T, TView>(
+                            eventArgs.Action,
+                            default,
+                            oldItem,
+                            eventArgs.NewStartingIndex,
+                            eventArgs.OldStartingIndex, // removed, uses same index
+                            eventArgs.SortOperation);
+
+                        observer.OnNext(newArgs);
+                    }
+                }
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewAdd<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<CollectionAddEvent<(T, TView)>>
+{
+    protected override IDisposable SubscribeCore(Observer<CollectionAddEvent<(T, TView)>> observer)
+    {
+        return new _SynchronizedViewAdd(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewAdd(
+        ISynchronizedView<T, TView> source,
+        Observer<CollectionAddEvent<(T, TView)>> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, CollectionAddEvent<(T, TView)>>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Add)
+            {
+                if (eventArgs.IsSingleItem)
+                {
+                    observer.OnNext(new CollectionAddEvent<(T, TView)>(eventArgs.NewStartingIndex, eventArgs.NewItem));
+                }
+                else
+                {
+                    var index = eventArgs.NewStartingIndex;
+                    for (int i = 0; i < eventArgs.NewValues.Length; i++)
+                    {
+                        observer.OnNext(new CollectionAddEvent<(T, TView)>(index++, (eventArgs.NewValues[i], eventArgs.NewViews[i])));
+                    }
+                }
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewRemove<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<CollectionRemoveEvent<(T, TView)>>
+{
+    protected override IDisposable SubscribeCore(Observer<CollectionRemoveEvent<(T, TView)>> observer)
+    {
+        return new _SynchronizedViewRemove(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewRemove(
+        ISynchronizedView<T, TView> source,
+        Observer<CollectionRemoveEvent<(T, TView)>> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, CollectionRemoveEvent<(T, TView)>>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Remove)
+            {
+                if (eventArgs.IsSingleItem)
+                {
+                    observer.OnNext(new CollectionRemoveEvent<(T, TView)>(eventArgs.OldStartingIndex, eventArgs.OldItem));
+                }
+                else
+                {
+                    for (int i = 0; i < eventArgs.OldValues.Length; i++)
+                    {
+                        observer.OnNext(new CollectionRemoveEvent<(T, TView)>(eventArgs.OldStartingIndex, (eventArgs.OldValues[i], eventArgs.OldViews[i])));
+                    }
+                }
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewReplace<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<CollectionReplaceEvent<(T, TView)>>
+{
+    protected override IDisposable SubscribeCore(Observer<CollectionReplaceEvent<(T, TView)>> observer)
+    {
+        return new _SynchronizedViewReplace(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewReplace(
+        ISynchronizedView<T, TView> source,
+        Observer<CollectionReplaceEvent<(T, TView)>> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, CollectionReplaceEvent<(T, TView)>>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Replace)
+            {
+                observer.OnNext(new CollectionReplaceEvent<(T, TView)>(eventArgs.NewStartingIndex, eventArgs.OldItem, eventArgs.NewItem));
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewMove<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<CollectionMoveEvent<(T, TView)>>
+{
+    protected override IDisposable SubscribeCore(Observer<CollectionMoveEvent<(T, TView)>> observer)
+    {
+        return new _SynchronizedViewMove(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewMove(
+        ISynchronizedView<T, TView> source,
+        Observer<CollectionMoveEvent<(T, TView)>> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, CollectionMoveEvent<(T, TView)>>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Move)
+            {
+                observer.OnNext(new CollectionMoveEvent<(T, TView)>(eventArgs.OldStartingIndex, eventArgs.NewStartingIndex, eventArgs.NewItem));
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewReset<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<CollectionResetEvent<T>>
+{
+    protected override IDisposable SubscribeCore(Observer<CollectionResetEvent<T>> observer)
+    {
+        return new _SynchronizedViewReset(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewReset(
+        ISynchronizedView<T, TView> source,
+        Observer<CollectionResetEvent<T>> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, CollectionResetEvent<T>>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Reset)
+            {
+                observer.OnNext(new CollectionResetEvent<T>(eventArgs.SortOperation));
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewClear<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<Unit>
+{
+    protected override IDisposable SubscribeCore(Observer<Unit> observer)
+    {
+        return new _SynchronizedViewClear(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewClear(
+        ISynchronizedView<T, TView> source,
+        Observer<Unit> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, Unit>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Reset && eventArgs.SortOperation.IsClear)
+            {
+                observer.OnNext(Unit.Default);
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewReverse<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<(int Index, int Count)>
+{
+    protected override IDisposable SubscribeCore(Observer<(int Index, int Count)> observer)
+    {
+        return new _SynchronizedViewReverse(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewReverse(
+        ISynchronizedView<T, TView> source,
+        Observer<(int Index, int Count)> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, (int Index, int Count)>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Reset && eventArgs.SortOperation.IsReverse)
+            {
+                observer.OnNext((eventArgs.SortOperation.Index, eventArgs.SortOperation.Count));
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewSort<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<(int Index, int Count, IComparer<T>? Comparer)>
+{
+    protected override IDisposable SubscribeCore(Observer<(int Index, int Count, IComparer<T>? Comparer)> observer)
+    {
+        return new _SynchronizedViewSort(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewSort(
+        ISynchronizedView<T, TView> source,
+        Observer<(int Index, int Count, IComparer<T>? Comparer)> observer,
+        CancellationToken cancellationToken)
+        : SynchronizedViewObserverBase<T, TView, (int Index, int Count, IComparer<T>? Comparer)>(source, observer, cancellationToken)
+    {
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            if (eventArgs.Action == NotifyCollectionChangedAction.Reset && eventArgs.SortOperation.IsSort)
+            {
+                observer.OnNext(eventArgs.SortOperation.AsTuple());
+            }
+        }
+    }
+}
+
+sealed class SynchronizedViewCountChanged<T, TView>(ISynchronizedView<T, TView> source, bool notifyCurrentCount, CancellationToken cancellationToken)
+    : Observable<int>
+{
+    protected override IDisposable SubscribeCore(Observer<int> observer)
+    {
+        return new _SynchronizedViewCountChanged(source, notifyCurrentCount, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewCountChanged : SynchronizedViewObserverBase<T, TView, int>
+    {
+        int countPrev;
+
+        public _SynchronizedViewCountChanged(
+            ISynchronizedView<T, TView> source,
+            bool notifyCurrentCount,
+            Observer<int> observer,
+            CancellationToken cancellationToken) : base(source, observer, cancellationToken)
+        {
+            this.countPrev = source.Count;
+            if (notifyCurrentCount)
+            {
+                observer.OnNext(source.Count);
+            }
+        }
+
+        protected override void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs)
+        {
+            switch (eventArgs.Action)
+            {
+                case NotifyCollectionChangedAction.Add:
+                case NotifyCollectionChangedAction.Remove:
+                case NotifyCollectionChangedAction.Reset when countPrev != source.Count:
+                    observer.OnNext(source.Count);
+                    break;
+            }
+            countPrev = source.Count;
+        }
+    }
+}
+
+
+
+sealed class SynchronizedViewRejected<T, TView>(ISynchronizedView<T, TView> source, CancellationToken cancellationToken)
+    : Observable<RejectedViewChangedEvent>
+{
+    protected override IDisposable SubscribeCore(Observer<RejectedViewChangedEvent> observer)
+    {
+        return new _SynchronizedViewRejected(source, observer, cancellationToken);
+    }
+
+    sealed class _SynchronizedViewRejected : IDisposable
+    {
+        readonly ISynchronizedView<T, TView> source;
+        readonly Observer<RejectedViewChangedEvent> observer;
+        readonly CancellationTokenRegistration cancellationTokenRegistration;
+        readonly Action<RejectedViewChangedAction, int, int> handlerDelegate;
+
+        public _SynchronizedViewRejected(ISynchronizedView<T, TView> source, Observer<RejectedViewChangedEvent> observer, CancellationToken cancellationToken)
+        {
+            this.source = source;
+            this.observer = observer;
+            this.handlerDelegate = Handler;
+
+            source.RejectedViewChanged += handlerDelegate;
+
+            if (cancellationToken.CanBeCanceled)
+            {
+                cancellationTokenRegistration = cancellationToken.UnsafeRegister(static state =>
+                {
+                    var s = (_SynchronizedViewRejected)state!;
+                    s.observer.OnCompleted();
+                    s.Dispose();
+                }, this);
+            }
+        }
+
+        public void Dispose()
+        {
+            source.RejectedViewChanged -= handlerDelegate;
+            cancellationTokenRegistration.Dispose();
+        }
+
+        void Handler(RejectedViewChangedAction rejectedViewChangedAction, int newIndex, int oldIndex)
+        {
+            observer.OnNext(new RejectedViewChangedEvent(rejectedViewChangedAction, newIndex, oldIndex));
+        }
+    }
+}
+
+abstract class SynchronizedViewObserverBase<T, TView, TEvent> : IDisposable
+{
+    protected readonly ISynchronizedView<T, TView> source;
+    protected readonly Observer<TEvent> observer;
+    readonly CancellationTokenRegistration cancellationTokenRegistration;
+    readonly NotifyViewChangedEventHandler<T, TView> handlerDelegate;
+
+    public SynchronizedViewObserverBase(ISynchronizedView<T, TView> source, Observer<TEvent> observer, CancellationToken cancellationToken)
+    {
+        this.source = source;
+        this.observer = observer;
+        this.handlerDelegate = Handler;
+
+        source.ViewChanged += handlerDelegate;
+
+        if (cancellationToken.CanBeCanceled)
+        {
+            cancellationTokenRegistration = cancellationToken.UnsafeRegister(static state =>
+            {
+                var s = (SynchronizedViewObserverBase<T, TView, TEvent>)state!;
+                s.observer.OnCompleted();
+                s.Dispose();
+            }, this);
+        }
+    }
+
+    public void Dispose()
+    {
+        source.ViewChanged -= handlerDelegate;
+        cancellationTokenRegistration.Dispose();
+    }
+
+    protected abstract void Handler(in SynchronizedViewChangedEventArgs<T, TView> eventArgs);
+}
\ No newline at end of file
diff --git a/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs b/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs
index 61f3f2a..21adea2 100644
--- a/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs
+++ b/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs
@@ -55,7 +55,7 @@ public readonly record struct DictionaryRemoveEvent<TKey, TValue>(TKey Key, TVal
 
 public readonly record struct DictionaryReplaceEvent<TKey, TValue>(TKey Key, TValue OldValue, TValue NewValue);
 
-public static class ObservableCollectionR3Extensions
+public static partial class ObservableCollectionR3Extensions
 {
     public static Observable<CollectionChangedEvent<T>> ObserveChanged<T>(this IObservableCollection<T> source, CancellationToken cancellationToken = default)
     {
@@ -165,7 +165,7 @@ sealed class ObservableCollectionChanged<T>(IObservableCollection<T> collection,
                     {
                         var newArgs = new CollectionChangedEvent<T>(
                             eventArgs.Action,
-                            eventArgs.NewItem,
+                            item,
                             eventArgs.OldItem,
                             i++,
                             eventArgs.OldStartingIndex,
@@ -181,7 +181,7 @@ sealed class ObservableCollectionChanged<T>(IObservableCollection<T> collection,
                         var newArgs = new CollectionChangedEvent<T>(
                             eventArgs.Action,
                             eventArgs.NewItem,
-                            eventArgs.OldItem,
+                            item,
                             eventArgs.NewStartingIndex,
                             eventArgs.OldStartingIndex, // removed, uses same index
                             eventArgs.SortOperation);