WAF ObservableListViewBase: restore original DeferCollectionChangedNo…

…tifications behavior
jbe2277 · Sep 25, 2023 · 0a10e0a · 0a10e0a
1 parent edfff41
commit 0a10e0a
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Showing 2 changed files with 17 additions and 29 deletions.
diff --git a/src/System.Waf/System.Waf/System.Waf.Core.Test/Foundation/ObservableListViewCoreTest.cs b/src/System.Waf/System.Waf/System.Waf.Core.Test/Foundation/ObservableListViewCoreTest.cs
@@ -255,6 +255,8 @@ public void RelayEventsWithDefer()
                 using (var deferral2 = observableListView.DeferCollectionChangedNotifications())
                 {
                     originalList.Add("first");
+                    Assert.AreEqual(1, collectionChangingList.Count);
+                    Assert.AreEqual(0, collectionChangedList.Count);
                     Assert.AreEqual(1, countChangedCount);
                     Assert.AreEqual(1, indexerChangedCount);
                     originalList.Add("second");
@@ -265,16 +267,15 @@ public void RelayEventsWithDefer()
                     originalList.Add("third");
 
                     countChangedCount = indexerChangedCount = 0;
-                    Assert.AreEqual(5, collectionChangingList.Count);
+                    Assert.AreEqual(1, collectionChangingList.Count);
                     Assert.AreEqual(0, collectionChangedList.Count);
                 }
-                Assert.AreEqual(5, collectionChangingList.Count);
+                Assert.AreEqual(1, collectionChangingList.Count);
                 Assert.AreEqual(0, collectionChangedList.Count);
                 deferral1.Dispose();  // call Dispose twice to see if this works too
             }
-            AssertHelper.SequenceEqual(new[] { NotifyCollectionChangedAction.Add, NotifyCollectionChangedAction.Add, NotifyCollectionChangedAction.Move, 
-                NotifyCollectionChangedAction.Remove, NotifyCollectionChangedAction.Add }, collectionChangedList.Select(x => x.Action));
-            AssertHelper.SequenceEqual(collectionChangedList, collectionChangingList);
+            Assert.AreEqual(NotifyCollectionChangedAction.Reset, collectionChangingList.Single().Action);
+            Assert.AreEqual(NotifyCollectionChangedAction.Reset, collectionChangedList.Single().Action);
             Assert.AreEqual(0, countChangedCount);
             Assert.AreEqual(0, indexerChangedCount);
         }

diff --git a/src/System.Waf/System.Waf/System.Waf.Core/Foundation/ObservableListViewBase.cs b/src/System.Waf/System.Waf/System.Waf.Core/Foundation/ObservableListViewBase.cs
@@ -11,10 +11,9 @@ namespace System.Waf.Foundation
     /// <typeparam name="T">The type of elements in the collection.</typeparam>
     public abstract class ObservableListViewBase<T> : ReadOnlyCollection<T>, IReadOnlyObservableList<T>, INotifyCollectionChanging
     {
-        private readonly object deferredChangesLock = new();
-        private List<NotifyCollectionChangedEventArgs>? deferredChanges;
+        private int deferredChanges;
         private int deferCount;
-        
+
         /// <summary>Initializes a new instance of the ObservableListViewBase class.</summary>
         /// <param name="originalList">Initialize the list view with the items from this list.</param>
         protected ObservableListViewBase(IEnumerable<T>? originalList) : base(new List<T>())
@@ -42,39 +41,27 @@ public IDisposable DeferCollectionChangedNotifications()
             Interlocked.Increment(ref deferCount);
             return new DisposedNotifier(() =>
             {
-                if (Interlocked.Decrement(ref deferCount) == 0)
+                if (Interlocked.Decrement(ref deferCount) == 0 && Interlocked.Exchange(ref deferredChanges, 0) > 0)
                 {
-                    List<NotifyCollectionChangedEventArgs>? replayChanges;
-                    lock (deferredChangesLock)
-                    {
-                        replayChanges = deferredChanges;
-                        deferredChanges = null;
-                    }
-                    if (replayChanges is not null)
-                    {
-                        foreach (var x in replayChanges) OnCollectionChanged(x);
-                    }
+                    OnCollectionChanged(EventArgsCache.ResetCollectionChanged);
                 }
             });
         }
 
         /// <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);
+        protected virtual void OnCollectionChanging(NotifyCollectionChangedEventArgs e)
+        {
+            if (deferCount <= 0) CollectionChanging?.Invoke(this, e);
+            else if (deferredChanges == 0) CollectionChanging?.Invoke(this, EventArgsCache.ResetCollectionChanged);
+        }
 
         /// <summary>Raises the CollectionChanged event with the provided arguments.</summary>
         /// <param name="e">Arguments of the event being raised.</param>
         protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
         {
-            if (deferCount > 0) 
-            { 
-                lock (deferredChangesLock)
-                {
-                    deferredChanges ??= new();
-                    deferredChanges.Add(e);
-                }
-            }
-            else { CollectionChanged?.Invoke(this, e); }
+            if (deferCount <= 0) CollectionChanged?.Invoke(this, e);
+            else Interlocked.Increment(ref deferredChanges);
         }
 
         /// <summary>Raises the PropertyChanged event with the provided arguments.</summary>