update CollectionView to use nullable object types

Author: w-ahmad

src/ItemsSource/CollectionView.Properties.cs

@@ -55,7 +55,7 @@ public IList Source
     /// </summary>
     /// <param name="index">The zero-based index of the item to get or set.</param>
     /// <returns>The item at the specified index.</returns>
-    public object this[int index]
+    public object? this[int index]
     {
         get => _view[index];
         set => _view[index] = value;
@@ -69,7 +69,7 @@ public object this[int index]
     /// <summary>
     /// Gets or sets the current item in the view.
     /// </summary>
-    public object CurrentItem
+    public object? CurrentItem
     {
         get => CurrentPosition > -1 && CurrentPosition < _view.Count ? _view[CurrentPosition] : null!;
         set => MoveCurrentTo(value);

src/ItemsSource/CollectionView.cs

@@ -15,11 +15,11 @@ namespace WinUI.TableView;
 /// <summary>
 /// A collection view implementation that supports filtering, sorting, and incremental loading.
 /// </summary>
-internal partial class CollectionView : ICollectionView, ISupportIncrementalLoading, INotifyPropertyChanged, IComparer<object>
+internal partial class CollectionView : ICollectionView, ISupportIncrementalLoading, INotifyPropertyChanged, IComparer<object?>
 {
     private IList _source = default!;
     private bool _allowLiveShaping;
-    private readonly List<object> _view = [];
+    private readonly List<object?> _view = [];
     private readonly ObservableCollection<FilterDescription> _filterDescriptions = [];
     private readonly ObservableCollection<SortDescription> _sortDescriptions = [];
     private CollectionChangedListener<CollectionView>? _collectionChangedListener;
@@ -259,7 +259,7 @@ private void HandleFilterChanged()
             }
         }
 
-        var viewHash = new HashSet<object>(_view);
+        var viewHash = new HashSet<object?>(_view);
         var viewIndex = 0;
         for (var index = 0; index < _source.Count; index++)
         {
@@ -442,7 +442,7 @@ public void CopyTo(object[] array, int arrayIndex)
     /// </summary>
     /// <param name="item">The item to locate in the collection.</param>
     /// <returns>The index of the item if found in the collection; otherwise, -1.</returns>
-    public int IndexOf(object item)
+    public int IndexOf(object? item)
     {
         return _view.IndexOf(item);
     }
@@ -464,7 +464,7 @@ public void Insert(int index, object item)
     /// </summary>
     /// <param name="item">The item to move to.</param>
     /// <returns>true if the operation is successful; otherwise, false.</returns>
-    public bool MoveCurrentTo(object item)
+    public bool MoveCurrentTo(object? item)
     {
         return item == CurrentItem || MoveCurrentToIndex(IndexOf(item));
     }
@@ -520,7 +520,7 @@ public bool MoveCurrentToPrevious()
     /// </summary>
     /// <param name="item">The item to remove.</param>
     /// <returns>true if the item was successfully removed; otherwise, false.</returns>
-    public bool Remove(object item)
+    public bool Remove(object? item)
     {
         if (IsReadOnly) throw new NotSupportedException("Collection is read-only.");