feat: add hierarchy (tree-view) support

src/ColumnFilterHandler.cs

@@ -41,7 +41,9 @@ public virtual IList<TableViewFilterItem> GetFilterItems(TableViewColumn column,
                     }));
             }
 
-            collectionView.Source = (column.TableView.ItemsSource as IEnumerable) ?? Enumerable.Empty<object>();
+            collectionView.Source = (_tableView.IsHierarchicalEnabled
+                ? (IEnumerable)_tableView.GetAllHierarchyItemsFlat().ToList()
+                : column.TableView.ItemsSource as IEnumerable) ?? Enumerable.Empty<object>();
 
             var items = _tableView.ShowFilterItemsCount ?
                         GetFilterItemsWithCount(column, searchText, collectionView) :

src/EventArgs/TableViewRowExpansionChangedEventArgs.cs

@@ -0,0 +1,34 @@
+using System;
+
+namespace WinUI.TableView;
+
+/// <summary>
+/// Provides data for the <see cref="TableView.RowExpanded"/> and <see cref="TableView.RowCollapsed"/> events.
+/// </summary>
+public sealed class TableViewRowExpansionChangedEventArgs : EventArgs
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TableViewRowExpansionChangedEventArgs"/> class.
+    /// </summary>
+    public TableViewRowExpansionChangedEventArgs(object item, int index, bool isExpanded)
+    {
+        Item = item;
+        Index = index;
+        IsExpanded = isExpanded;
+    }
+
+    /// <summary>
+    /// Gets the item whose expansion state changed.
+    /// </summary>
+    public object Item { get; }
+
+    /// <summary>
+    /// Gets the index of the item in the display list.
+    /// </summary>
+    public int Index { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the item is now expanded.
+    /// </summary>
+    public bool IsExpanded { get; }
+}

src/ItemsSource/CollectionView.Properties.cs

@@ -8,6 +8,21 @@ namespace WinUI.TableView;
 
 partial class CollectionView
 {
+    /// <summary>
+    /// Gets or sets a value indicating whether sort descriptions should be ignored when
+    /// rebuilding the view. Set by <see cref="TableView"/> when hierarchical mode is active
+    /// so that per-level sorting is applied during flattening instead of globally.
+    /// </summary>
+    internal bool BypassSort { get; set; }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether filter descriptions should be ignored when
+    /// rebuilding the view. Set by <see cref="TableView"/> when hierarchical mode is active
+    /// so that subtree-aware filtering is applied during hierarchy flattening instead of
+    /// the flat per-item filter used in normal mode.
+    /// </summary>
+    internal bool BypassFilter { get; set; }
+
     /// <summary>
     /// Gets or sets the source collection.
     /// </summary>

src/ItemsSource/CollectionView.cs

@@ -255,7 +255,7 @@ private void OnItemPropertyChanged(object? item, PropertyChangedEventArgs e)
             return;
         }
 
-        if (FilterDescriptions.Any(fd => string.IsNullOrEmpty(fd.PropertyName) || fd.PropertyName == e.PropertyName))
+        if (!BypassFilter && FilterDescriptions.Any(fd => string.IsNullOrEmpty(fd.PropertyName) || fd.PropertyName == e.PropertyName))
         {
             var filterResult = FilterDescriptions.All(x => x.Predicate(item));
             var viewIndex = _view.IndexOf(item);
@@ -318,7 +318,7 @@ private void HandleSourceChanged()
 
         if (Source is not null)
         {
-            if (FilterDescriptions.Count > 0)
+            if (!BypassFilter && FilterDescriptions.Count > 0)
             {
                 foreach (var item in Source)
                 {
@@ -331,7 +331,7 @@ private void HandleSourceChanged()
                 _view.AddRange(_source.OfType<object>());
             }
 
-            if (SortDescriptions.Count > 0)
+            if (SortDescriptions.Count > 0 && !BypassSort)
                 _view.Sort(this);
         }
 
@@ -344,6 +344,8 @@ private void HandleSourceChanged()
     /// </summary>
     private void HandleFilterChanged()
     {
+        if (BypassFilter) return;
+
         if (FilterDescriptions.Count > 0)
         {
             for (var index = 0; index < _view.Count; index++)
@@ -384,24 +386,26 @@ private void HandleFilterChanged()
     /// </summary>
     private void HandleSortChanged()
     {
-        if (SortDescriptions.Count > 0)
+        if (!BypassSort)
         {
-            _view.Sort(this);
-        }
-        else
-        {
-            HandleSourceChanged();
-        }
+            if (SortDescriptions.Count > 0)
+                _view.Sort(this);
+            else
+                HandleSourceChanged();
 
-        OnVectorChanged(new VectorChangedEventArgs(CollectionChange.Reset));
+            OnVectorChanged(new VectorChangedEventArgs(CollectionChange.Reset));
+        }
+        // When BypassSort is true the external caller (TableView) handles the full
+        // rebuild via RebuildHierarchyView(). Firing VectorChanged here would trigger
+        // a stale RebuildDisplayedItems() before the hierarchy is re-flattened.
     }
 
     /// <summary>
     /// Handles the addition of an item to the collection.
     /// </summary>
     private bool HandleItemAdded(int newStartingIndex, object? newItem, int? viewIndex = null)
     {
-        if (!FilterDescriptions.All(x => x.Predicate(newItem)))
+        if (!BypassFilter && !FilterDescriptions.All(x => x.Predicate(newItem)))
         {
             return false;
         }

src/Strings/en-US/WinUI.TableView.resw

@@ -180,4 +180,10 @@
   <data name="Copy" xml:space="preserve">
     <value>Copy</value>
   </data>
+  <data name="ExpandRow" xml:space="preserve">
+    <value>Expand row</value>
+  </data>
+  <data name="CollapseRow" xml:space="preserve">
+    <value>Collapse row</value>
+  </data>
 </root>

src/TableView.Events.cs

@@ -271,4 +271,30 @@ protected internal virtual void OnColumnReordered(TableViewColumnReorderedEventA
     {
         ColumnReordered?.Invoke(this, args);
     }
-}
+
+    /// <summary>
+    /// Occurs when a row is expanded in hierarchical mode.
+    /// </summary>
+    public event EventHandler<TableViewRowExpansionChangedEventArgs>? RowExpanded;
+
+    /// <summary>
+    /// Occurs when a row is collapsed in hierarchical mode.
+    /// </summary>
+    public event EventHandler<TableViewRowExpansionChangedEventArgs>? RowCollapsed;
+
+    /// <summary>
+    /// Called when a row is expanded.
+    /// </summary>
+    protected internal virtual void OnRowExpanded(TableViewRowExpansionChangedEventArgs args)
+    {
+        RowExpanded?.Invoke(this, args);
+    }
+
+    /// <summary>
+    /// Called when a row is collapsed.
+    /// </summary>
+    protected internal virtual void OnRowCollapsed(TableViewRowExpansionChangedEventArgs args)
+    {
+        RowCollapsed?.Invoke(this, args);
+    }
+}