WritableNotifyCollectionChanged supports Add

README.md

@@ -374,14 +374,59 @@ public interface IWritableSynchronizedView<T, TView> : ISynchronizedView<T, TVie
 `ToWritableNotifyCollectionChanged` accepts a delegate called `WritableViewChangedEventHandler`. `newView` receives the newly bound value. If `setValue` is true, it sets a new value to the original collection, triggering notification propagation. The View is also regenerated. If `T originalValue` is a reference type, you can prevent such propagation by setting `setValue` to `false`.
 
 ```csharp
-var list = new ObservableList<int>();
-var view = list.CreateWritableView(x => x.ToString());
-view.AttachFilter(x => x % 2 == 0);
-IList<string> notify = view.ToWritableNotifyCollectionChanged((string newView, int originalValue, ref bool setValue) =>
+var list = new ObservableList<Person>()
 {
-    setValue = true; // or false
-    return int.Parse(newView);
+    new (){ Age = 10, Name = "John" },
+    new (){ Age = 22, Name = "Jeyne" },
+    new (){ Age = 30, Name = "Mike" },
+};
+var view = list.CreateWritableView(x => x.Name);
+view.AttachFilter(x => x.Age >= 20);
+
+IList<string?> bindable = view.ToWritableNotifyCollectionChanged((string? newView, Person original, ref bool setValue) =>
+{
+    if (setValue)
+    {
+        // default setValue == true is Set operation
+        original.Name = newView;
+
+        // You can modify setValue to false, it does not set original collection to new value.
+        // For mutable reference types, when there is only a single,
+        // bound View and to avoid recreating the View, setting false is effective.
+        // Otherwise, keeping it true will set the value in the original collection as well,
+        // and change notifications will be sent to lower-level Views(the delegate for View generation will also be called anew).
+        setValue = false;
+        return original;
+    }
+    else
+    {
+        // default setValue == false is Add operation
+        return new Person { Age = null, Name = newView };
+    }
 });
+
+bindable[1] = "Bob"; // change Mike(filtered view's [1]) to Bob.
+bindable.Add("Ken");
+
+// Show Views
+foreach (var item in view)
+{
+    Console.WriteLine(item);
+}
+
+Console.WriteLine("---");
+
+// Show Originals
+foreach (var item in list)
+{
+    Console.WriteLine((item.Age, item.Name));
+}
+
+public class Person
+{
+    public int? Age { get; set; }
+    public string? Name { get; set; }
+}
 ```
 
 Unity

sandbox/ConsoleApp/ConsoleApp.csproj

@@ -2,7 +2,7 @@
 
 	<PropertyGroup>
 		<OutputType>Exe</OutputType>
-        <TargetFramework>net6.0</TargetFramework>
+		<TargetFramework>net8.0</TargetFramework>
 		<LangVersion>10.0</LangVersion>
 		<Nullable>enable</Nullable>
 		<IsPackable>false</IsPackable>

sandbox/ConsoleApp/Program.cs

@@ -6,30 +6,59 @@ using ObservableCollections;
 using System.Collections;
 using System.Collections.Generic;
 using System.Threading.Tasks.Sources;
+using System.Reflection.Emit;
 
-var l = new ObservableList<int>();
-var view = l.CreateWritableView(x => x.ToString());
-view.AttachFilter(x => x % 2 == 0);
-IList<string> notify = view.ToWritableNotifyCollectionChanged((string newView, int originalValue, ref bool setValue) =>
+var list = new ObservableList<Person>()
 {
+    new (){ Age = 10, Name = "John" },
+    new (){ Age = 22, Name = "Jeyne" },
+    new (){ Age = 30, Name = "Mike" },
+};
+var view = list.CreateWritableView(x => x.Name);
+view.AttachFilter(x => x.Age >= 20);
+
+IList<string?> bindable = view.ToWritableNotifyCollectionChanged((string? newView, Person original, ref bool setValue) =>
+{
+    if (setValue)
+    {
+        // default setValue == true is Set operation
+        original.Name = newView;
+
+        // You can modify setValue to false, it does not set original collection to new value.
+        // For mutable reference types, when there is only a single,
+        // bound View and to avoid recreating the View, setting false is effective.
+        // Otherwise, keeping it true will set the value in the original collection as well,
+        // and change notifications will be sent to lower-level Views(the delegate for View generation will also be called anew).
         setValue = false;
-    return int.Parse(newView);
+        return original;
+    }
+    else
+    {
+        // default setValue == false is Add operation
+        return new Person { Age = null, Name = newView };
+    }
 });
 
-l.Add(0);
-l.Add(1);
-l.Add(2);
-l.Add(3);
-l.Add(4);
-l.Add(5);
-
-notify[1] = "99999";
+// bindable[0] = "takoyaki";
 
 foreach (var item in view)
 {
     Console.WriteLine(item);
 }
 
+Console.WriteLine("---");
+
+foreach (var item in list)
+{
+    Console.WriteLine((item.Age, item.Name));
+}
+
+public class Person
+{
+    public int? Age { get; set; }
+    public string? Name { get; set; }
+}
+
 
 //var buffer = new ObservableFixedSizeRingBuffer<int>(5);
 

src/ObservableCollections/IObservableCollection.cs

@@ -56,6 +56,7 @@ namespace ObservableCollections
         (T Value, TView View) GetAt(int index);
         void SetViewAt(int index, TView view);
         void SetToSourceCollection(int index, T value);
+        void AddToSourceCollection(T value);
         IWritableSynchronizedViewList<TView> ToWritableViewList(WritableViewChangedEventHandler<T, TView> converter);
         INotifyCollectionChangedSynchronizedViewList<TView> ToWritableNotifyCollectionChanged(WritableViewChangedEventHandler<T, TView> converter);
         INotifyCollectionChangedSynchronizedViewList<TView> ToWritableNotifyCollectionChanged(ICollectionEventDispatcher? collectionEventDispatcher);

src/ObservableCollections/ObservableList.Views.cs

@@ -360,6 +360,14 @@ namespace ObservableCollections
                 }
             }
 
+            public void AddToSourceCollection(T value)
+            {
+                lock (SyncRoot)
+                {
+                    source.Add(value);
+                }
+            }
+
             public IWritableSynchronizedViewList<TView> ToWritableViewList(WritableViewChangedEventHandler<T, TView> converter)
             {
                 return new FiltableWritableSynchronizedViewList<T, TView>(this, converter);

src/ObservableCollections/SynchronizedViewList.cs

@@ -557,7 +557,7 @@ internal class FiltableWritableSynchronizedViewList<T, TView> : FiltableSynchron
 
                 if (setValue)
                 {
-                    writableView.SetToSourceCollection(index, newOriginal);
+                    writableView.SetToSourceCollection(originalIndex, newOriginal);
                 }
             }
         }
@@ -695,7 +695,7 @@ internal class NotifyCollectionChangedSynchronizedViewList<T, TView> :
         get => ((IReadOnlyList<TView>)this)[index];
         set
         {
-            if (converter == null || parent is not IWritableSynchronizedView<T,TView> writableView)
+            if (converter == null || parent is not IWritableSynchronizedView<T, TView> writableView)
             {
                 throw new NotSupportedException("This CollectionView does not support set. If base type is ObservableList<T>, you can use ToWritableSynchronizedView and ToWritableNotifyCollectionChanged.");
             }
@@ -713,7 +713,7 @@ internal class NotifyCollectionChangedSynchronizedViewList<T, TView> :
 
                 if (setValue)
                 {
-                    writableView.SetToSourceCollection(index, newOriginal);
+                    writableView.SetToSourceCollection(originalIndex, newOriginal);
                 }
             }
         }
@@ -743,12 +743,24 @@ internal class NotifyCollectionChangedSynchronizedViewList<T, TView> :
 
     public void Add(TView item)
     {
-        throw new NotSupportedException();
+        if (converter == null || parent is not IWritableSynchronizedView<T, TView> writableView)
+        {
+            throw new NotSupportedException("This CollectionView does not support Add. If base type is ObservableList<T>, you can use ToWritableSynchronizedView and ToWritableNotifyCollectionChanged.");
+        }
+        else
+        {
+            var setValue = false;
+            var newOriginal = converter(item, default!, ref setValue);
+
+            // always add
+            writableView.AddToSourceCollection(newOriginal);
+        }
     }
 
     public int Add(object? value)
     {
-        throw new NotImplementedException();
+        Add((TView)value!);
+        return -1; // itself does not add in this collection
     }
 
     public void Clear()
@@ -1020,12 +1032,24 @@ internal class NonFilteredNotifyCollectionChangedSynchronizedViewList<T, TView>
 
     public void Add(TView item)
     {
-        throw new NotSupportedException();
+        if (converter == null || parent is not IWritableSynchronizedView<T, TView> writableView)
+        {
+            throw new NotSupportedException("This CollectionView does not support Add. If base type is ObservableList<T>, you can use ToWritableSynchronizedView and ToWritableNotifyCollectionChanged.");
+        }
+        else
+        {
+            var setValue = false;
+            var newOriginal = converter(item, default!, ref setValue);
+
+            // always add
+            writableView.AddToSourceCollection(newOriginal);
+        }
     }
 
     public int Add(object? value)
     {
-        throw new NotImplementedException();
+        Add((TView)value!);
+        return -1; // itself does not add in this collection
     }
 
     public void Clear()