SharpTreeView.cs

// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Threading;

namespace ICSharpCode.TreeView
{
	public class SharpTreeView : ListView
	{
		static SharpTreeView()
		{
			DefaultStyleKeyProperty.OverrideMetadata(typeof(SharpTreeView),
			                                         new FrameworkPropertyMetadata(typeof(SharpTreeView)));

			SelectionModeProperty.OverrideMetadata(typeof(SharpTreeView),
			                                       new FrameworkPropertyMetadata(SelectionMode.Extended));

			AlternationCountProperty.OverrideMetadata(typeof(SharpTreeView),
			                                          new FrameworkPropertyMetadata(2));

			DefaultItemContainerStyleKey =
				new ComponentResourceKey(typeof(SharpTreeView), "DefaultItemContainerStyleKey");

			VirtualizingStackPanel.VirtualizationModeProperty.OverrideMetadata(typeof(SharpTreeView),
			                                                                   new FrameworkPropertyMetadata(VirtualizationMode.Recycling));

			RegisterCommands();
		}

		public static ResourceKey DefaultItemContainerStyleKey { get; private set; }

		public SharpTreeView()
		{
			SetResourceReference(ItemContainerStyleProperty, DefaultItemContainerStyleKey);
		}

		public static readonly DependencyProperty CanDragAndDropProperty =
			DependencyProperty.Register("CanDragAndDrop", typeof(bool), typeof(SharpTreeView), new PropertyMetadata(true));
		public bool CanDragAndDrop {
			get { return (bool)GetValue(CanDragAndDropProperty); }
			set { SetValue(CanDragAndDropProperty, value); }
		}

		public static readonly DependencyProperty RootProperty =
			DependencyProperty.Register("Root", typeof(SharpTreeNode), typeof(SharpTreeView));

		public SharpTreeNode Root
		{
			get { return (SharpTreeNode)GetValue(RootProperty); }
			set { SetValue(RootProperty, value); }
		}

		public static readonly DependencyProperty ShowRootProperty =
			DependencyProperty.Register("ShowRoot", typeof(bool), typeof(SharpTreeView),
			                            new FrameworkPropertyMetadata(true));

		public bool ShowRoot
		{
			get { return (bool)GetValue(ShowRootProperty); }
			set { SetValue(ShowRootProperty, value); }
		}

		public static readonly DependencyProperty ShowRootExpanderProperty =
			DependencyProperty.Register("ShowRootExpander", typeof(bool), typeof(SharpTreeView),
			                            new FrameworkPropertyMetadata(false));

		public bool ShowRootExpander
		{
			get { return (bool)GetValue(ShowRootExpanderProperty); }
			set { SetValue(ShowRootExpanderProperty, value); }
		}

		public static readonly DependencyProperty AllowDropOrderProperty =
			DependencyProperty.Register("AllowDropOrder", typeof(bool), typeof(SharpTreeView));

		public bool AllowDropOrder
		{
			get { return (bool)GetValue(AllowDropOrderProperty); }
			set { SetValue(AllowDropOrderProperty, value); }
		}

		public static readonly DependencyProperty ShowLinesProperty =
			DependencyProperty.Register("ShowLines", typeof(bool), typeof(SharpTreeView),
			                            new FrameworkPropertyMetadata(true));

		public bool ShowLines
		{
			get { return (bool)GetValue(ShowLinesProperty); }
			set { SetValue(ShowLinesProperty, value); }
		}

		public static bool GetShowAlternation(DependencyObject obj)
		{
			return (bool)obj.GetValue(ShowAlternationProperty);
		}

		public static void SetShowAlternation(DependencyObject obj, bool value)
		{
			obj.SetValue(ShowAlternationProperty, value);
		}

		public static readonly DependencyProperty ShowAlternationProperty =
			DependencyProperty.RegisterAttached("ShowAlternation", typeof(bool), typeof(SharpTreeView),
			                                    new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.Inherits));

		protected override void OnPropertyChanged(DependencyPropertyChangedEventArgs e)
		{
			base.OnPropertyChanged(e);
			if (e.Property == RootProperty ||
			    e.Property == ShowRootProperty ||
			    e.Property == ShowRootExpanderProperty) {
				Reload();
			}
		}

		TreeFlattener flattener;
		bool updatesLocked;

		public IDisposable LockUpdates() => new UpdateLock(this);

		class UpdateLock : IDisposable
		{
			SharpTreeView instance;

			public UpdateLock(SharpTreeView instance)
			{
				this.instance = instance;
				this.instance.updatesLocked = true;
			}

			public void Dispose() => instance.updatesLocked = false;
		}

		void Reload()
		{
			if (flattener != null) {
				flattener.Stop();
				flattener.CollectionChanged -= flattener_CollectionChanged;
			}
			if (Root != null) {
				if (!(ShowRoot && ShowRootExpander)) {
					Root.IsExpanded = true;
				}
				flattener = new TreeFlattener(Root, ShowRoot);
				flattener.CollectionChanged += flattener_CollectionChanged;
				this.ItemsSource = flattener;
			}
		}

		void flattener_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
		{
			// Deselect nodes that are being hidden, if any remain in the tree
			if (e.Action == NotifyCollectionChangedAction.Remove && Items.Count > 0) {
				List<SharpTreeNode> selectedOldItems = null;
				foreach (SharpTreeNode node in e.OldItems) {
					if (node.IsSelected) {
						if (selectedOldItems == null)
							selectedOldItems = new List<SharpTreeNode>();
						selectedOldItems.Add(node);
					}
				}
				if (!updatesLocked && selectedOldItems != null) {
					var list = SelectedItems.Cast<SharpTreeNode>().Except(selectedOldItems).ToList();
					UpdateFocusedNode(list, Math.Max(0, e.OldStartingIndex - 1));
				}
			}
		}

		void UpdateFocusedNode(List<SharpTreeNode> newSelection, int topSelectedIndex)
		{
			if (updatesLocked) return;
			SetSelectedItems(newSelection ?? Enumerable.Empty<SharpTreeNode>());
			if (SelectedItem == null) {
				SelectedIndex = topSelectedIndex;
				if (SelectedItem != null && IsKeyboardFocusWithin)
					FocusNode((SharpTreeNode)SelectedItem);
			}
		}

		protected override void ClearContainerForItemOverride(DependencyObject element, object item) {
			var item2 = element as SharpTreeViewItem;
			if (item2 != null) {
				var nv = item2.NodeView;
				if (nv != null)
					nv.DataContext = null;
				item2.ClearValue(DataContextProperty);
			}
			base.ClearContainerForItemOverride(element, item);
		}

		protected override DependencyObject GetContainerForItemOverride()
		{
			return new SharpTreeViewItem();
		}

		protected override bool IsItemItsOwnContainerOverride(object item)
		{
			return item is SharpTreeViewItem;
		}

		protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
		{
			base.PrepareContainerForItemOverride(element, item);
			SharpTreeViewItem container = element as SharpTreeViewItem;
			container.ParentTreeView = this;
			// Make sure that the line renderer takes into account the new bound data
			if (container.NodeView != null && container.NodeView.LinesRenderer != null) {
				container.NodeView.LinesRenderer.InvalidateVisual();
			}
		}

		bool doNotScrollOnExpanding;

		/// <summary>
		/// Handles the node expanding event in the tree view.
		/// This method gets called only if the node is in the visible region (a SharpTreeNodeView exists).
		/// </summary>
		internal void HandleExpanding(SharpTreeNode node)
		{
			if (doNotScrollOnExpanding)
				return;
			SharpTreeNode lastVisibleChild = node;
			while (true) {
				SharpTreeNode tmp = lastVisibleChild.Children.LastOrDefault(c => c.IsVisible);
				if (tmp != null) {
					lastVisibleChild = tmp;
				} else {
					break;
				}
			}
			if (lastVisibleChild != node) {
				Debug.Assert(flattener != null);
				if (flattener == null)
					return;
				// A new scrollViewer.ViewportHeight value is available at the earliest at Render prio.
				// If there are many empty lines, it will equal the number of visible items (eg. 5,
				// but viewport can show eg. 10).
				Dispatcher.BeginInvoke(DispatcherPriority.Render, new Action(() => {
					var itemsPerPage = STVUTILS.GetItemsPerPage(this, 0);
					int nodeIndex = flattener.IndexOf(node);
					int lastVisibleChildIndex = flattener.IndexOf(lastVisibleChild);
					Debug.Assert(nodeIndex >= 0 && lastVisibleChildIndex >= 0);
					if (itemsPerPage > 0 && nodeIndex >= 0 && lastVisibleChildIndex >= 0) {
						int lastIndex = Math.Min(lastVisibleChildIndex, nodeIndex + itemsPerPage - 1);
						ScrollIntoView(Items[lastIndex]);
						Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new Action(() => ScrollIntoView(node)));
					}
				}));
			}
		}

		static class STVUTILS {
			static T FindVisualChild<T>(DependencyObject obj) where T : DependencyObject {
				int childrenCount = VisualTreeHelper.GetChildrenCount(obj);
				for (int i = 0; i < childrenCount; i++) {
					var child = VisualTreeHelper.GetChild(obj, i);
					if (child is T res)
						return res;

					res = FindVisualChild<T>(child);
					if (res != null)
						return res;
				}

				return null;
			}

			public static ScrollViewer TryGetScrollViewer(ListBox lb) => FindVisualChild<ScrollViewer>(lb);

			public static int GetItemsPerPage(ListBox lb, int defaultValue) {
				var scrollViewer = TryGetScrollViewer(lb);
				if (scrollViewer == null)
					return defaultValue;
				return (int)Math.Max(1, Math.Floor(scrollViewer.ViewportHeight));
			}
		}

		protected override void OnKeyDown(KeyEventArgs e)
		{
			SharpTreeViewItem container = e.OriginalSource as SharpTreeViewItem;
			if (container != null && container.Node != null) switch (e.Key) {
				case Key.Left:
					if (container != null && ItemsControl.ItemsControlFromItemContainer(container) == this) {
						if (container.Node.IsExpanded) {
							container.Node.IsExpanded = false;
						} else if (container.Node.Parent != null) {
							this.FocusNode(container.Node.Parent);
						}
						e.Handled = true;
					}
					break;
				case Key.Right:
					if (container != null && ItemsControl.ItemsControlFromItemContainer(container) == this) {
						if (!container.Node.IsExpanded && container.Node.ShowExpander) {
							container.Node.IsExpanded = true;
						} else if (container.Node.Children.Count > 0) {
							// jump to first child:
							container.MoveFocus(new TraversalRequest(FocusNavigationDirection.Down));
						}
						e.Handled = true;
					}
					break;
				case Key.Return:
					if (container != null && Keyboard.Modifiers == ModifierKeys.None && this.SelectedItems.Count == 1 && this.SelectedItem == container.Node) {
						e.Handled = true;
						container.Node.ActivateItem(e);
					}
					break;
				case Key.Space:
					if (container != null && Keyboard.Modifiers == ModifierKeys.None && this.SelectedItems.Count == 1 && this.SelectedItem == container.Node) {
						e.Handled = true;
						if (container.Node.IsCheckable) {
							if (container.Node.IsChecked == null) // If partially selected, we want to select everything
								container.Node.IsChecked = true;
							else
								container.Node.IsChecked = !container.Node.IsChecked;
						} else {
							container.Node.ActivateItem(e);
						}
					}
					break;
				case Key.Add:
					if (container != null && ItemsControl.ItemsControlFromItemContainer(container) == this) {
						container.Node.IsExpanded = true;
						e.Handled = true;
					}
					break;
				case Key.Subtract:
					if (container != null && ItemsControl.ItemsControlFromItemContainer(container) == this) {
						container.Node.IsExpanded = false;
						e.Handled = true;
					}
					break;
				case Key.Multiply:
					if (container != null && ItemsControl.ItemsControlFromItemContainer(container) == this) {
						container.Node.IsExpanded = true;
						ExpandRecursively(container.Node);
						e.Handled = true;
					}
					break;
				case Key.Back:
					if (IsTextSearchEnabled) {
						var instance = SharpTreeViewTextSearch.GetInstance(this);
						if (instance != null) {
							instance.RevertLastCharacter();
							e.Handled = true;
						}
					}
					break;
			}
			if (!e.Handled)
				base.OnKeyDown(e);
		}

		protected override void OnTextInput(TextCompositionEventArgs e)
		{
			if (!string.IsNullOrEmpty(e.Text) && IsTextSearchEnabled && (e.OriginalSource == this || ItemsControl.ItemsControlFromItemContainer(e.OriginalSource as DependencyObject) == this)) {
				var instance = SharpTreeViewTextSearch.GetInstance(this);
				if (instance != null) {
					instance.Search(e.Text);
					e.Handled = true;
				}
			}
			if (!e.Handled)
				base.OnTextInput(e);
		}

		void ExpandRecursively(SharpTreeNode node)
		{
			if (node.CanExpandRecursively) {
				node.IsExpanded = true;
				foreach (SharpTreeNode child in node.Children) {
					ExpandRecursively(child);
				}
			}
		}

		/// <summary>
		/// Scrolls the specified node in view and sets keyboard focus on it.
		/// </summary>
		public void FocusNode(SharpTreeNode node)
		{
			if (node == null)
				throw new ArgumentNullException("node");
			ScrollIntoView(node);
			// WPF's ScrollIntoView() uses the same if/dispatcher construct, so we call OnFocusItem() after the item was brought into view.
			if (this.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated) {
				OnFocusItem(node);
			} else {
				this.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new DispatcherOperationCallback(this.OnFocusItem), node);
			}
		}

		public void ScrollIntoView(SharpTreeNode node)
		{
			if (node == null)
				throw new ArgumentNullException("node");
			doNotScrollOnExpanding = true;
			foreach (SharpTreeNode ancestor in node.Ancestors())
				ancestor.IsExpanded = true;
			doNotScrollOnExpanding = false;
			base.ScrollIntoView(node);
		}

		object OnFocusItem(object item)
		{
			FrameworkElement element = this.ItemContainerGenerator.ContainerFromItem(item) as FrameworkElement;
			if (element != null) {
				element.Focus();
			}
			return null;
		}

		protected override System.Windows.Automation.Peers.AutomationPeer OnCreateAutomationPeer() => new SharpTreeViewAutomationPeer(this);

		#region Track selection

		protected override void OnSelectionChanged(SelectionChangedEventArgs e)
		{
			foreach (SharpTreeNode node in e.RemovedItems) {
				node.IsSelected = false;
			}
			foreach (SharpTreeNode node in e.AddedItems) {
				node.IsSelected = true;
			}
			base.OnSelectionChanged(e);
		}

		#endregion

		#region Drag and Drop
		protected override void OnDragEnter(DragEventArgs e)
		{
			OnDragOver(e);
		}

		protected override void OnDragOver(DragEventArgs e)
		{
			e.Effects = DragDropEffects.None;

			if (Root != null && !ShowRoot) {
				e.Handled = true;
				Root.CanDrop(e, Root.Children.Count);
			}
		}

		protected override void OnDrop(DragEventArgs e)
		{
			e.Effects = DragDropEffects.None;

			if (Root != null && !ShowRoot) {
				e.Handled = true;
				Root.InternalDrop(e, Root.Children.Count);
			}
		}

		internal void HandleDragEnter(SharpTreeViewItem item, DragEventArgs e)
		{
			HandleDragOver(item, e);
		}

		internal void HandleDragOver(SharpTreeViewItem item, DragEventArgs e)
		{
			HidePreview();

			var target = GetDropTarget(item, e);
			if (target != null) {
				e.Handled = true;
				ShowPreview(target.Item, target.Place);
			}

			var sv = STVUTILS.TryGetScrollViewer(this);
			double tolerance = item.NodeView.ActualHeight / 2;
			double verticalPos = e.GetPosition(this).Y;

			// take the difference between tolerance and position to scroll more rapidly as tolerance gap closes
			if (verticalPos < tolerance) {
				sv.ScrollToVerticalOffset(sv.VerticalOffset - (tolerance - verticalPos));
			}
			else if (verticalPos > ActualHeight - tolerance) {
				sv.ScrollToVerticalOffset(sv.VerticalOffset + (verticalPos - ActualHeight + tolerance));
			}
		}

		internal void HandleDrop(SharpTreeViewItem item, DragEventArgs e)
		{
			try {
				HidePreview();

				var target = GetDropTarget(item, e);
				if (target != null) {
					e.Handled = true;
					target.Node.InternalDrop(e, target.Index);
				}
			} catch (Exception ex) {
				Debug.WriteLine(ex.ToString());
				throw;
			}
		}

		internal void HandleDragLeave(SharpTreeViewItem item, DragEventArgs e)
		{
			HidePreview();
			e.Handled = true;
		}

		class DropTarget
		{
			public SharpTreeViewItem Item;
			public DropPlace Place;
			public double Y;
			public SharpTreeNode Node;
			public int Index;
		}

		DropTarget GetDropTarget(SharpTreeViewItem item, DragEventArgs e)
		{
			var dropTargets = BuildDropTargets(item, e);
			var y = e.GetPosition(item).Y;
			foreach (var target in dropTargets) {
				if (target.Y >= y) {
					return target;
				}
			}
			return null;
		}

		List<DropTarget> BuildDropTargets(SharpTreeViewItem item, DragEventArgs e)
		{
			var result = new List<DropTarget>();
			var node = item.Node;

			if (AllowDropOrder) {
				TryAddDropTarget(result, item, DropPlace.Before, e);
			}

			TryAddDropTarget(result, item, DropPlace.Inside, e);

			if (AllowDropOrder) {
				if (node != null && node.IsExpanded && node.Children.Count > 0) {
					var firstChildItem = ItemContainerGenerator.ContainerFromItem(node.Children[0]) as SharpTreeViewItem;
					TryAddDropTarget(result, firstChildItem, DropPlace.Before, e);
				}
				else {
					TryAddDropTarget(result, item, DropPlace.After, e);
				}
			}

			var h = item.ActualHeight;
			var y1 = 0.2 * h;
			var y2 = h / 2;
			var y3 = h - y1;

			if (result.Count == 2) {
				if (result[0].Place == DropPlace.Inside &&
				    result[1].Place != DropPlace.Inside) {
					result[0].Y = y3;
				}
				else if (result[0].Place != DropPlace.Inside &&
				         result[1].Place == DropPlace.Inside) {
					result[0].Y = y1;
				}
				else {
					result[0].Y = y2;
				}
			}
			else if (result.Count == 3) {
				result[0].Y = y1;
				result[1].Y = y3;
			}
			if (result.Count > 0) {
				result[result.Count - 1].Y = h;
			}
			return result;
		}

		void TryAddDropTarget(List<DropTarget> targets, SharpTreeViewItem item, DropPlace place, DragEventArgs e)
		{
			SharpTreeNode node;
			int index;

			GetNodeAndIndex(item, place, out node, out index);

			if (node != null) {
				e.Effects = DragDropEffects.None;
				if (node.CanDrop(e, index)) {
					DropTarget target = new DropTarget() {
						Item = item,
						Place = place,
						Node = node,
						Index = index
					};
					targets.Add(target);
				}
			}
		}

		void GetNodeAndIndex(SharpTreeViewItem item, DropPlace place, out SharpTreeNode node, out int index)
		{
			node = null;
			index = 0;

			if (item.Node == null) {
			}
			else if (place == DropPlace.Inside) {
				node = item.Node;
				index = node.Children.Count;
			}
			else if (place == DropPlace.Before) {
				if (item.Node.Parent != null) {
					node = item.Node.Parent;
					index = node.Children.IndexOf(item.Node);
				}
			}
			else {
				if (item.Node.Parent != null) {
					node = item.Node.Parent;
					index = node.Children.IndexOf(item.Node) + 1;
				}
			}
		}

		SharpTreeNodeView previewNodeView;
		InsertMarker insertMarker;
		DropPlace previewPlace;

		enum DropPlace
		{
			Before, Inside, After
		}

		public Func<Brush> GetPreviewInsideTextBackground = () => SystemColors.HighlightBrush;
		public Func<Brush> GetPreviewInsideForeground = () => SystemColors.HighlightTextBrush;

		void ShowPreview(SharpTreeViewItem item, DropPlace place)
		{
			previewNodeView = item.NodeView;
			previewPlace = place;

			if (place == DropPlace.Inside) {
				previewNodeView.TextBackground = GetPreviewInsideTextBackground();
				previewNodeView.Foreground = GetPreviewInsideForeground();
			}
			else {
				if (insertMarker == null) {
					var adornerLayer = AdornerLayer.GetAdornerLayer(this);
					var adorner = new GeneralAdorner(this);
					insertMarker = new InsertMarker();
					adorner.Child = insertMarker;
					adornerLayer.Add(adorner);
				}

				insertMarker.Visibility = Visibility.Visible;

				var p1 = previewNodeView.TransformToVisual(this).Transform(new Point());
				var p = new Point(p1.X + previewNodeView.CalculateIndent(item.Node) + 4.5, p1.Y - 3);

				if (place == DropPlace.After) {
					p.Y += previewNodeView.ActualHeight;
				}

				insertMarker.Margin = new Thickness(p.X, p.Y, 0, 0);

				SharpTreeNodeView secondNodeView = null;
				var index = flattener.IndexOf(item.Node);

				if (place == DropPlace.Before) {
					if (index > 0) {
						secondNodeView = (ItemContainerGenerator.ContainerFromIndex(index - 1) as SharpTreeViewItem)?.NodeView;
					}
				}
				else if (index + 1 < flattener.Count) {
					secondNodeView = (ItemContainerGenerator.ContainerFromIndex(index + 1) as SharpTreeViewItem)?.NodeView;
				}

				var w = p1.X + previewNodeView.ActualWidth - p.X;

				if (secondNodeView != null) {
					var p2 = secondNodeView.TransformToVisual(this).Transform(new Point());
					w = Math.Max(w, p2.X + secondNodeView.ActualWidth - p.X);
				}

				insertMarker.Width = w + 10;
			}
		}

		void HidePreview()
		{
			if (previewNodeView != null) {
				previewNodeView.ClearValue(SharpTreeNodeView.TextBackgroundProperty);
				previewNodeView.ClearValue(SharpTreeNodeView.ForegroundProperty);
				if (insertMarker != null) {
					insertMarker.Visibility = Visibility.Collapsed;
				}
				previewNodeView = null;
			}
		}
		#endregion

		#region Cut / Copy / Paste / Delete Commands

		static void RegisterCommands()
		{
			// The asm editor should be the only one removing nodes
// 			CommandManager.RegisterClassCommandBinding(typeof(SharpTreeView),
// 			                                           new CommandBinding(ApplicationCommands.Cut, HandleExecuted_Cut, HandleCanExecute_Cut));
//
// 			CommandManager.RegisterClassCommandBinding(typeof(SharpTreeView),
// 			                                           new CommandBinding(ApplicationCommands.Copy, HandleExecuted_Copy, HandleCanExecute_Copy));
//
// 			CommandManager.RegisterClassCommandBinding(typeof(SharpTreeView),
// 			                                           new CommandBinding(ApplicationCommands.Paste, HandleExecuted_Paste, HandleCanExecute_Paste));
//
// 			CommandManager.RegisterClassCommandBinding(typeof(SharpTreeView),
// 			                                           new CommandBinding(ApplicationCommands.Delete, HandleExecuted_Delete, HandleCanExecute_Delete));
		}

		static void HandleExecuted_Cut(object sender, ExecutedRoutedEventArgs e)
		{

		}

		static void HandleCanExecute_Cut(object sender, CanExecuteRoutedEventArgs e)
		{
			e.CanExecute = false;
		}

		static void HandleExecuted_Copy(object sender, ExecutedRoutedEventArgs e)
		{

		}

		static void HandleCanExecute_Copy(object sender, CanExecuteRoutedEventArgs e)
		{
			e.CanExecute = false;
		}

		static void HandleExecuted_Paste(object sender, ExecutedRoutedEventArgs e)
		{

		}

		static void HandleCanExecute_Paste(object sender, CanExecuteRoutedEventArgs e)
		{
			e.CanExecute = false;
		}

		static void HandleExecuted_Delete(object sender, ExecutedRoutedEventArgs e)
		{
			SharpTreeView treeView = (SharpTreeView)sender;
			treeView.updatesLocked = true;
			int selectedIndex = -1;
			try {
				foreach (SharpTreeNode node in treeView.GetTopLevelSelection().ToArray()) {
					if (selectedIndex == -1)
						selectedIndex = treeView.flattener.IndexOf(node);
					node.Delete();
				}
			} finally {
				treeView.updatesLocked = false;
				treeView.UpdateFocusedNode(null, Math.Max(0, selectedIndex - 1));
			}
		}

		static void HandleCanExecute_Delete(object sender, CanExecuteRoutedEventArgs e)
		{
			SharpTreeView treeView = (SharpTreeView)sender;
			e.CanExecute = treeView.GetTopLevelSelection().All(node => node.CanDelete());
		}

		/// <summary>
		/// Gets the selected items which do not have any of their ancestors selected.
		/// </summary>
		public IEnumerable<SharpTreeNode> GetTopLevelSelection()
		{
			var selection = this.SelectedItems.OfType<SharpTreeNode>().ToHashSet();
			return selection.Where(item => item.Ancestors().All(a => !selection.Contains(a)));
		}

		#endregion

		public void SetSelectedNodes(IEnumerable<SharpTreeNode> nodes)
		{
			this.SetSelectedItems(nodes.ToList());
		}
	}
}