WAF ReadOnlyObservableList implements INotifyCollectionChanging

src/System.Waf/System.Waf/Directory.Build.props

@@ -2,7 +2,7 @@
   <Import Project="$([MSBuild]::GetPathOfFileAbove($(MSBuildThisFile), $(MSBuildThisFileDirectory)../))" />
 
   <PropertyGroup>
-    <LangVersion>8.0</LangVersion>
+    <LangVersion>9.0</LangVersion>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
 
     <Authors>jbe2277</Authors>

src/System.Waf/System.Waf/System.Waf.Core.Test/Foundation/ReadOnlyObservableListTest.cs

@@ -1,4 +1,5 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
 using System.Collections.ObjectModel;
 using System.Collections.Specialized;
 using System.ComponentModel;
@@ -10,30 +11,50 @@ namespace Test.Waf.Foundation
     public class ReadOnlyObservableListTest
     {
         [TestMethod]
-        public void ChangedEventsTest()
+        public void ObservableCollectionChangedEventsTest() => ChangedEventsTestCore(new ObservableCollection<string>(), false);
+
+        [TestMethod]
+        public void ObservableListChangedEventsTest() => ChangedEventsTestCore(new ObservableList<string>(), true);
+
+        private static void ChangedEventsTestCore(ObservableCollection<string> list, bool supportsCollectionChanging)
         {
-            var list = new ObservableCollection<string>();
             var readOnlyList = new ReadOnlyObservableList<string>(list);
 
+            int collectionChangingCalled = 0;            
             int collectionChangedCalled = 0;
-            void CollectionChangedHandler(object? sender, NotifyCollectionChangedEventArgs e) => collectionChangedCalled++;
             int countPropertyChangedCalled = 0;
-            void PropertyChangedHandler(object? sender, PropertyChangedEventArgs e)
-            {
-                if (e.PropertyName == nameof(readOnlyList.Count)) countPropertyChangedCalled++;
-            }
-
+
+            if (supportsCollectionChanging) readOnlyList.CollectionChanging += CollectionChangingHandler;
+            else Assert.ThrowsException<NotSupportedException>(() => readOnlyList.CollectionChanging += CollectionChangingHandler);
             readOnlyList.CollectionChanged += CollectionChangedHandler;
             readOnlyList.PropertyChanged += PropertyChangedHandler;
             list.Add("Hello");
+            if (supportsCollectionChanging) Assert.AreEqual(1, collectionChangingCalled);
             Assert.AreEqual(1, collectionChangedCalled);
             Assert.AreEqual(1, countPropertyChangedCalled);
 
+            readOnlyList.CollectionChanging -= CollectionChangingHandler;
             readOnlyList.CollectionChanged -= CollectionChangedHandler;
             readOnlyList.PropertyChanged -= PropertyChangedHandler;
             list.Add("World");
+            if (supportsCollectionChanging) Assert.AreEqual(1, collectionChangingCalled);
             Assert.AreEqual(1, collectionChangedCalled);
             Assert.AreEqual(1, countPropertyChangedCalled);
+
+            void CollectionChangingHandler(object? sender, NotifyCollectionChangedEventArgs e) { Assert.AreSame(readOnlyList, sender); collectionChangingCalled++; }
+            void CollectionChangedHandler(object? sender, NotifyCollectionChangedEventArgs e) { Assert.AreSame(readOnlyList, sender); collectionChangedCalled++; }
+            void PropertyChangedHandler(object? sender, PropertyChangedEventArgs e)
+            {
+                Assert.AreSame(readOnlyList, sender);
+                if (e.PropertyName == nameof(readOnlyList.Count)) countPropertyChangedCalled++;
+            }
+        }
+
+        [TestMethod]
+        public void EmptyPropertyTest()
+        {
+            var readOnlyList = ReadOnlyObservableList<string>.Empty;
+            Assert.AreEqual(0, readOnlyList.Count);
         }
     }
 }

src/System.Waf/System.Waf/System.Waf.Core/Foundation/ReadOnlyObservableList.cs

@@ -9,29 +9,55 @@ namespace System.Waf.Foundation
     /// This class implements the IReadOnlyObservableList interface and provides public CollectionChanged and PropertyChanged events.
     /// </summary>
     /// <typeparam name="T">The type of elements in the collection.</typeparam>
-    public class ReadOnlyObservableList<T> : ReadOnlyObservableCollection<T>, IReadOnlyObservableList<T>
+    public class ReadOnlyObservableList<T> : ReadOnlyObservableCollection<T>, INotifyCollectionChanging, IReadOnlyObservableList<T>
     {
+        private readonly bool collectionChangingSupported;
+        [NonSerialized] private NotifyCollectionChangedEventHandler? collectionChanging;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ReadOnlyObservableCollection{T}"/>
         /// class that serves as a wrapper around the specified <see cref="ObservableCollection{T}"/>.
         /// </summary>
         /// <param name="list">The <see cref="ObservableCollection{T}"/> with which to create this instance of the 
         /// <see cref="ReadOnlyObservableCollection{T}"/> class.</param>
         /// <exception cref="ArgumentNullException">list is null.</exception>
-        public ReadOnlyObservableList(ObservableCollection<T> list) : base(list) { }
+        public ReadOnlyObservableList(ObservableCollection<T> list) : base(list)
+        {
+            if (list is INotifyCollectionChanging x) { collectionChangingSupported = true; x.CollectionChanging += HandleCollectionChanging; }
+        }
+
+        /// <summary>Gets an empty <see cref="ReadOnlyObservableList{T}"/>.</summary>
+        /// <remarks>The returned instance is immutable and will always be empty.</remarks>
+        public static ReadOnlyObservableList<T> Empty { get; } = new(new ObservableList<T>());
+
+        private void CheckCollectionChanging() { if (!collectionChangingSupported) throw new NotSupportedException("CollectionChanging event is not supported by the underlying list."); }
 
-        /// <summary>Occurs when the collection changes.</summary>
+        /// <inheritdoc />
+        /// <exception cref="NotSupportedException">CollectionChanging event is not supported by the underlying list.</exception>
+        public event NotifyCollectionChangedEventHandler? CollectionChanging
+        {
+            add { CheckCollectionChanging(); collectionChanging += value; }
+            remove { collectionChanging -= value; }
+        }
+
+        /// <inheritdoc />
         public new event NotifyCollectionChangedEventHandler? CollectionChanged
         {
             add => base.CollectionChanged += value;
             remove => base.CollectionChanged -= value;
         }
 
-        /// <summary>Occurs when a property value changes.</summary>
+        /// <inheritdoc />
         public new event PropertyChangedEventHandler? PropertyChanged
         {
             add => base.PropertyChanged += value;
             remove => base.PropertyChanged -= value;
         }
+
+        /// <summary>Raises the CollectionChanged event with the provided arguments.</summary>
+        /// <param name="e">Arguments of the event being raised.</param>
+        protected virtual void OnCollectionChanging(NotifyCollectionChangedEventArgs e) => collectionChanging?.Invoke(this, e);
+
+        private void HandleCollectionChanging(object? sender, NotifyCollectionChangedEventArgs e) => OnCollectionChanging(e);        
     }
 }

src/System.Waf/System.Waf/System.Waf.Core/GlobalSuppressions.cs

@@ -38,5 +38,5 @@
 [assembly: SuppressMessage("Security", "CA2109:Review visible event handlers", Justification = "<Pending>", Scope = "member", Target = "~M:System.Waf.Foundation.SynchronizingCollectionCore`2.OriginalCollectionChanged(System.Object,System.Collections.Specialized.NotifyCollectionChangedEventArgs)")]
 [assembly: SuppressMessage("Design", "CA1030:Use events where appropriate", Justification = "<Pending>", Scope = "member", Target = "~M:System.Waf.Foundation.Model.RaisePropertyChanged(System.String[])")]
 [assembly: SuppressMessage("Maintainability", "CA1508:Avoid dead conditional code", Justification = "<Pending>", Scope = "member", Target = "~M:System.Waf.Foundation.Model.RaisePropertyChanged(System.String[])")]
-[assembly: SuppressMessage("Usage", "CA2249:Consider using 'string.Contains' instead of 'string.IndexOf'", Justification = "<Pending>", Scope = "member", Target = "~M:System.Waf.Foundation.StringHelper.Contains(System.String,System.String,System.StringComparison)~System.Boolean")]
 [assembly: SuppressMessage("Globalization", "CA1307:Specify StringComparison for clarity", Justification = "<Pending>", Scope = "member", Target = "~M:System.Waf.Foundation.ValidatableModel.ValidationResultComparer.GetHashCode(System.ComponentModel.DataAnnotations.ValidationResult)~System.Int32")]
+[assembly: SuppressMessage("Design", "CA1000:Do not declare static members on generic types", Justification = "<Pending>", Scope = "member", Target = "~P:System.Waf.Foundation.ReadOnlyObservableList`1.Empty")]