Fix: AdvancedCollection inserts at wrong position when adding to end of source collection

components/Collections/src/AdvancedCollectionView/AdvancedCollectionView.cs

@@ -698,7 +698,7 @@ private bool HandleItemAdded(int newStartingIndex, object newItem, int? viewInde
             }
             else if (newStartingIndex == _source.Count - 1)
             {
-                newViewIndex = _view.Count - 1;
+                newViewIndex = _view.Count;
             }
             else if (viewIndex.HasValue)
             {

components/Collections/tests/Test_AdvancedCollectionView.cs

@@ -80,6 +80,9 @@ public void Test_SourceNcc_CollectionChanged_Add()
         ObservableCollection<SampleClass> col = new ObservableCollection<SampleClass>();
         AdvancedCollectionView acv = new AdvancedCollectionView(col, true);
 
+        Assert.AreEqual(0, col.Count);
+        Assert.AreEqual(0, acv.Count);
+
         // Add all items to collection while DeferRefresh() is active:
         using (acv.DeferRefresh())
         {
@@ -89,11 +92,49 @@ public void Test_SourceNcc_CollectionChanged_Add()
             }
         }
 
+        Assert.AreNotEqual(0, col.Count);
+        Assert.AreNotEqual(0, acv.Count);
+
+        Assert.AreEqual(refList.Count, col.Count);
+        Assert.AreEqual(refList.Count, acv.Count);
+
+        // Make sure each item added to source is in the expected place in the view:
+        for (int i = 0; i < refList.Count; i++)
+        {
+            var sourceItem = col[i];
+            var collectionViewItem = (SampleClass)acv[i];
+
+            Assert.AreEqual(sourceItem.Val, collectionViewItem.Val);
+        }
+
         // Check if subscribed to all items:
         foreach (var item in refList)
         {
             Assert.IsTrue(item.GetPropertyChangedEventHandlerSubscriberLength() == 1);
         }
+
+        // Add a filter and item to filter
+        var itemToFilter = new SampleClass(1000);
+        Func<object, bool> filter = x => ((SampleClass)x).Val == itemToFilter.Val;
+        acv.Filter = x => !filter(x);
+        col.Add(itemToFilter);
+
+        var filteredItemInAcv = (SampleClass?)acv.FirstOrDefault(filter);
+        Assert.IsNull(filteredItemInAcv, $"Filtered item unexpectedly included in collection view: {filteredItemInAcv?.Val}.");
+
+        col.Remove(itemToFilter);
+
+        // With filter set, create and add an item that isn't filtered
+        var itemToNotFilter = new SampleClass(itemToFilter.Val + 1);
+        col.Add(itemToNotFilter);
+
+        var addedItemInAcv = (SampleClass?)acv.FirstOrDefault(x => ((SampleClass)x).Val == itemToNotFilter.Val);
+
+        Assert.IsNotNull(addedItemInAcv, $"Unfiltered item unexpectedly filtered out of collection view: {addedItemInAcv?.Val}.");
+
+        // Ensure added (not filtered) item is added to the last position in view.
+        var indexOfNotFilteredItemInAcv = acv.IndexOf(addedItemInAcv);
+        Assert.AreEqual(acv.Count - 1, indexOfNotFilteredItemInAcv, "Unfiltered item added to source collection not last in view.");
     }
 
     [TestCategory("Helpers")]