ICSharpCode.TreeView: improve API for drag/drop/copy/paste of nodes.

src/AddIns/BackendBindings/XamlBinding/XamlBinding/XamlOutlineNode.cs

@@ -36,22 +36,12 @@ namespace ICSharpCode.XamlBinding
 		public ITextAnchor EndMarker { get; set; }
 		public ITextEditor Editor { get; set; }
 		
-		public override bool CanDrag(SharpTreeNode[] nodes)
-		{
-			return false; //nodes.All(node => node.Parent != null);
-		}
-		
-		public override bool CanDrop(DragEventArgs e, int index)
-		{
-			return false;
-		}
-		
 		public string GetMarkupText()
 		{
 			return Editor.Document.GetText(Marker.Offset, EndMarker.Offset - Marker.Offset);
 		}
 		
-		public override IDataObject Copy(SharpTreeNode[] nodes)
+		protected override IDataObject GetDataObject(SharpTreeNode[] nodes)
 		{
 			string[] data = nodes
 				.OfType<XamlOutlineNode>()
@@ -63,11 +53,6 @@ namespace ICSharpCode.XamlBinding
 			return dataObject;
 		}
 		
-		public override bool CanDelete()
-		{
-			return Parent != null;
-		}
-		
 //		public override void Drop(IDataObject data, int index, DropEffect finalEffect)
 //		{
 //			try {
@@ -96,12 +81,24 @@ namespace ICSharpCode.XamlBinding
 //			}
 //		}
 		
-		public override void Delete()
+		public override bool CanDelete(SharpTreeNode[] nodes)
+		{
+			return nodes.OfType<XamlOutlineNode>().All(n => n.Parent != null);
+		}
+		
+		public override void Delete(SharpTreeNode[] nodes)
 		{
-			DeleteCore();
+			DeleteWithoutConfirmation(nodes);
+		}
+		
+		public override void DeleteWithoutConfirmation(SharpTreeNode[] nodes)
+		{
+			foreach (XamlOutlineNode xamlNode in nodes.OfType<XamlOutlineNode>()) {
+				xamlNode.DeleteCore();
+			}
 		}
 		
-		public override void DeleteCore()
+		void DeleteCore()
 		{
 			Editor.Document.Remove(Marker.Offset, EndMarker.Offset - Marker.Offset);
 		}

src/AddIns/Debugger/Debugger.AddIn/Pads/WatchPad.cs

@@ -132,29 +132,20 @@ namespace ICSharpCode.SharpDevelop.Gui.Pads
 	
 	class WatchRootNode : SharpTreeNode
 	{
-		public override bool CanDrop(DragEventArgs e, int index)
+		public override bool CanPaste(IDataObject data)
 		{
-			e.Effects = DragDropEffects.None;
-			if (e.Data.GetDataPresent(DataFormats.StringFormat)) {
-				e.Effects = DragDropEffects.Copy;
-				return true;
-			}
-			return false;
+			return data.GetDataPresent(DataFormats.StringFormat);
 		}
 		
-		public override void Drop(DragEventArgs e, int index)
+		public override void Paste(IDataObject data)
 		{
-			if (e.Data == null) return;
-			if (!e.Data.GetDataPresent(DataFormats.StringFormat)) return;
-			
-			var watchValue = e.Data.GetData(DataFormats.StringFormat).ToString();
+			var watchValue = data.GetData(DataFormats.StringFormat) as string;
 			if (string.IsNullOrEmpty(watchValue)) return;
 			
 			var pad = SD.Workbench.GetPad(typeof(WatchPad)).PadContent as WatchPad;
 			if (pad == null) return;
 			
 			pad.AddWatch(watchValue);
-			WindowsDebugger.RefreshPads();
 		}
 	}
 	

src/AddIns/Debugger/Debugger.AddIn/TreeModel/SharpTreeNodeAdapter.cs

@@ -35,14 +35,16 @@ namespace Debugger.AddIn.Pads.Controls
 			get { return this.Node.GetChildren != null; }
 		}
 		
-		public override bool CanDelete()
+		public override bool CanDelete(SharpTreeNode[] nodes)
 		{
-			return this.Node.CanDelete;
+			return nodes.All(n => n is SharpTreeNodeAdapter)
+				&& nodes.Cast<SharpTreeNodeAdapter>().All(n => n.Node.CanDelete);
 		}
 		
-		public override void Delete()
+		public override void Delete(SharpTreeNode[] nodes)
 		{
-			Parent.Children.Remove(this);
+			foreach (var node in nodes)
+				node.Parent.Children.Remove(this);
 		}
 		
 		protected override void LoadChildren()

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichText.cs

@@ -158,19 +158,24 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 				int endOffset = i + 1 < stateChangeOffsets.Length ? stateChangeOffsets[i + 1] : text.Length;
 				Run r = new Run(text.Substring(startOffset, endOffset - startOffset));
 				HighlightingColor state = stateChanges[i];
-				if (state.Foreground != null)
-					r.Foreground = state.Foreground.GetBrush(null);
-				if (state.Background != null)
-					r.Background = state.Background.GetBrush(null);
-				if (state.FontWeight != null)
-					r.FontWeight = state.FontWeight.Value;
-				if (state.FontStyle != null)
-					r.FontStyle = state.FontStyle.Value;
+				ApplyColorToTextElement(r, state);
 				runs[i] = r;
 			}
 			return runs;
 		}
 
+		internal static void ApplyColorToTextElement(TextElement r, HighlightingColor state)
+		{
+			if (state.Foreground != null)
+				r.Foreground = state.Foreground.GetBrush(null);
+			if (state.Background != null)
+				r.Background = state.Background.GetBrush(null);
+			if (state.FontWeight != null)
+				r.FontWeight = state.FontWeight.Value;
+			if (state.FontStyle != null)
+				r.FontStyle = state.FontStyle.Value;
+		}
+		
 		/// <summary>
 		/// Produces HTML code for the line, with &lt;span style="..."&gt; tags.
 		/// </summary>

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs

@@ -7,6 +7,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Windows;
+using System.Windows.Documents;
 using System.Windows.Media;
 using ICSharpCode.NRefactory.Editor;
 using ICSharpCode.NRefactory.TypeSystem.Implementation;
@@ -264,5 +265,23 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 				index++;
 			}
 		}
+		
+		/// <summary>
+		/// Creates WPF Run instances that can be used for TextBlock.Inlines.
+		/// </summary>
+		/// <param name="textSource">The text source that holds the text for this RichTextModel.</param>
+		public Run[] CreateRuns(ITextSource textSource)
+		{
+			Run[] runs = new Run[stateChanges.Count];
+			for (int i = 0; i < runs.Length; i++) {
+				int startOffset = stateChangeOffsets[i];
+				int endOffset = i + 1 < stateChangeOffsets.Count ? stateChangeOffsets[i + 1] : textSource.TextLength;
+				Run r = new Run(textSource.GetText(startOffset, endOffset - startOffset));
+				HighlightingColor state = stateChanges[i];
+				RichText.ApplyColorToTextElement(r, state);
+				runs[i] = r;
+			}
+			return runs;
+		}
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/RichTextWriter.cs

@@ -9,6 +9,9 @@ using ICSharpCode.AvalonEdit.Highlighting;
 
 namespace ICSharpCode.AvalonEdit.Utils
 {
+	// TODO: This class (and derived classes) is currently unused; decide whether to keep it.
+	// (until this is decided, keep the class internal)
+	
 	/// <summary>
 	/// A text writer that supports creating spans of highlighted text.
 	/// </summary>

src/Libraries/SharpTreeView/ICSharpCode.TreeView.Demo/FileNode.cs

@@ -84,10 +84,15 @@ namespace ICSharpCode.TreeView.Demo
 		{
 			get { return info.FullName; }
 		}
-//
-//		public override void Paste(IDataObject data)
-//		{
-//			Parent.Paste(data);
-//		}
+
+		public override bool CanPaste(IDataObject data)
+		{
+			return Parent.CanPaste(data);
+		}
+		
+		public override void Paste(IDataObject data)
+		{
+			Parent.Paste(data);
+		}
 	}
 }

src/Libraries/SharpTreeView/ICSharpCode.TreeView.Demo/FileSystemNode.cs

@@ -29,46 +29,40 @@ namespace ICSharpCode.TreeView.Demo
 		{
 			return FullPath;
 		}
-//
-//		public override bool CanCopy(SharpTreeNode[] nodes)
-//		{
-//			return true;
-//		}
 
-		public override IDataObject Copy(SharpTreeNode[] nodes)
+		public override bool CanCopy(SharpTreeNode[] nodes)
+		{
+			return nodes.All(n => n is FileSystemNode);
+		}
+		
+		protected override IDataObject GetDataObject(SharpTreeNode[] nodes)
 		{
 			var data = new DataObject();
 			var paths = nodes.OfType<FileSystemNode>().Select(n => n.FullPath).ToArray();
-			data.SetData(typeof(string[]), paths);
+			data.SetData(DataFormats.FileDrop, paths);
 			return data;
 		}
-//
-//		public override bool CanPaste(IDataObject data)
-//		{
-//			return true;
-//		}
-//
-		public override bool CanDelete()
+		
+		public override bool CanDelete(SharpTreeNode[] nodes)
 		{
-			return true;
+			return nodes.All(n => n is FileSystemNode);
 		}
 		
-		public override void Delete()
+		public override void Delete(SharpTreeNode[] nodes)
 		{
-			if (MessageBox.Show("Sure?", "Delete", MessageBoxButton.OKCancel) == MessageBoxResult.OK) {
-				DeleteCore();
+			if (MessageBox.Show("Are you sure you want to delete " + nodes.Length + " items?", "Delete", MessageBoxButton.OKCancel) == MessageBoxResult.OK) {
+				DeleteWithoutConfirmation(nodes);
 			}
 		}
 		
-		public override void DeleteCore()
+		public override void DeleteWithoutConfirmation(SharpTreeNode[] nodes)
 		{
-			this.Parent.Children.Remove(this);
+			foreach (var node in nodes) {
+				if (node.Parent != null)
+					node.Parent.Children.Remove(node);
+			}
 		}
 
-		public override bool CanDrag(SharpTreeNode[] nodes)
-		{
-			return true;
-		}
 		
 //		ContextMenu menu;
 //

src/Libraries/SharpTreeView/ICSharpCode.TreeView.Demo/FolderNode.cs

@@ -63,11 +63,11 @@ namespace ICSharpCode.TreeView.Demo
 		{
 			try {
 				foreach (var p in Directory.GetDirectories(path)
-					.OrderBy(d => Path.GetDirectoryName(d))) {
+				         .OrderBy(d => Path.GetDirectoryName(d))) {
 					Children.Add(new FolderNode(p));
 				}
 				foreach (var p in Directory.GetFiles(path)
-					.OrderBy(f => Path.GetFileName(f))) {
+				         .OrderBy(f => Path.GetFileName(f))) {
 					Children.Add(new FileNode(p));
 				}
 			}
@@ -75,22 +75,34 @@ namespace ICSharpCode.TreeView.Demo
 			}
 		}
 		
-		public override bool CanDrop(DragEventArgs e, int index)
+		public override bool CanPaste(IDataObject data)
 		{
-			return e.Data.GetDataPresent(typeof(string[]));
+			return data.GetDataPresent(DataFormats.FileDrop);
 		}
 		
-		public override void Drop(DragEventArgs e, int index)
+		public override void Paste(IDataObject data)
 		{
-			var paths = e.Data.GetData(typeof(string[])) as string[];
+			var paths = data.GetData(DataFormats.FileDrop) as string[];
 			if (paths != null) {
-				for (int i = 0; i < paths.Length; i++) {
-					var p = paths[i];
+				foreach (var p in paths) {
 					if (File.Exists(p)) {
-						Children.Insert(index + i, new FileNode(p));
+						Children.Add(new FileNode(p));
+					} else {
+						Children.Add(new FolderNode(p));
 					}
-					else {
-						Children.Insert(index + i, new FolderNode(p));
+				}
+			}
+		}
+		
+		public override void Drop(DragEventArgs e, int index)
+		{
+			var paths = e.Data.GetData(DataFormats.FileDrop) as string[];
+			if (paths != null) {
+				foreach (var p in paths) {
+					if (File.Exists(p)) {
+						Children.Insert(index++, new FileNode(p));
+					} else {
+						Children.Insert(index++, new FolderNode(p));
 					}
 				}
 			}

src/Libraries/SharpTreeView/ICSharpCode.TreeView/SharpTreeNode.cs

@@ -441,7 +441,10 @@ namespace ICSharpCode.TreeView
 		
 		#region Cut / Copy / Paste / Delete
 		
-		public bool IsCut { get { return false; } }
+		/// <summary>
+		/// Gets whether the node should render transparently because it is 'cut' (but not actually removed yet).
+		/// </summary>
+		public virtual bool IsCut { get { return false; } }
 		/*
 			static List<SharpTreeNode> cuttedNodes = new List<SharpTreeNode>();
 			static IDataObject cuttedData;
@@ -538,66 +541,99 @@ namespace ICSharpCode.TreeView
 			}
 		 */
 		
-		public virtual bool CanDelete()
+		public virtual bool CanDelete(SharpTreeNode[] nodes)
 		{
 			return false;
 		}
 		
-		public virtual void Delete()
+		public virtual void Delete(SharpTreeNode[] nodes)
 		{
 			throw new NotSupportedException(GetType().Name + " does not support deletion");
 		}
 		
-		public virtual void DeleteCore()
+		public virtual void DeleteWithoutConfirmation(SharpTreeNode[] nodes)
 		{
 			throw new NotSupportedException(GetType().Name + " does not support deletion");
 		}
 		
-		public virtual IDataObject Copy(SharpTreeNode[] nodes)
+		public virtual bool CanCut(SharpTreeNode[] nodes)
 		{
-			throw new NotSupportedException(GetType().Name + " does not support copy/paste or drag'n'drop");
+			return CanCopy(nodes) && CanDelete(nodes);
 		}
 		
-		/*
-			public virtual bool CanCopy(SharpTreeNode[] nodes)
-			{
-				return false;
+		public virtual void Cut(SharpTreeNode[] nodes)
+		{
+			var data = GetDataObject(nodes);
+			if (data != null) {
+				// TODO: default cut implementation should not immediately perform deletion, but use 'IsCut'
+				Clipboard.SetDataObject(data, copy: true);
+				DeleteWithoutConfirmation(nodes);
 			}
+		}
 		
-			public virtual bool CanPaste(IDataObject data)
-			{
-				return false;
-			}
+		public virtual bool CanCopy(SharpTreeNode[] nodes)
+		{
+			return false;
+		}
 		
-			public virtual void Paste(IDataObject data)
-			{
-				EnsureLazyChildren();
-				Drop(data, Children.Count, DropEffect.Copy);
-			}
-		 */
-		#endregion
+		public virtual void Copy(SharpTreeNode[] nodes)
+		{
+			var data = GetDataObject(nodes);
+			if (data != null)
+				Clipboard.SetDataObject(data, copy: true);
+		}
 		
-		#region Drag and Drop
-		public virtual bool CanDrag(SharpTreeNode[] nodes)
+		protected virtual IDataObject GetDataObject(SharpTreeNode[] nodes)
+		{
+			return null;
+		}
+		
+		public virtual bool CanPaste(IDataObject data)
 		{
 			return false;
 		}
 		
+		public virtual void Paste(IDataObject data)
+		{
+			throw new NotSupportedException(GetType().Name + " does not support copy/paste");
+		}
+		#endregion
+		
+		#region Drag and Drop
 		public virtual void StartDrag(DependencyObject dragSource, SharpTreeNode[] nodes)
 		{
-			DragDropEffects effects = DragDropEffects.All;
-			if (!nodes.All(n => n.CanDelete()))
-				effects &= ~DragDropEffects.Move;
-			DragDropEffects result = DragDrop.DoDragDrop(dragSource, Copy(nodes), effects);
+			// The default drag implementation works by reusing the copy infrastructure.
+			// Derived classes should override this method
+			var data = GetDataObject(nodes);
+			if (data == null)
+				return;
+			DragDropEffects effects = DragDropEffects.Copy;
+			if (CanDelete(nodes))
+				effects |= DragDropEffects.Move;
+			DragDropEffects result = DragDrop.DoDragDrop(dragSource, data, effects);
 			if (result == DragDropEffects.Move) {
-				foreach (SharpTreeNode node in nodes)
-					node.DeleteCore();
+				DeleteWithoutConfirmation(nodes);
 			}
 		}
 		
-		public virtual bool CanDrop(DragEventArgs e, int index)
+		/// <summary>
+		/// Gets the possible drop effects.
+		/// If the method returns more than one of (Copy|Move|Link), the tree view will choose one effect based
+		/// on the allowed effects and keyboard status.
+		/// </summary>
+		public virtual DragDropEffects GetDropEffect(DragEventArgs e, int index)
 		{
-			return false;
+			// Since the default drag implementation uses Copy(),
+			// we'll use Paste() in our default drop implementation.
+			if (CanPaste(e.Data)) {
+				// If Ctrl is pressed -> copy
+				// If moving is not allowed -> copy
+				// Otherwise: move
+				if ((e.KeyStates & DragDropKeyStates.ControlKey) != 0 || (e.AllowedEffects & DragDropEffects.Move) == 0)
+					return DragDropEffects.Copy;
+				return DragDropEffects.Move;
+			}
+			return DragDropEffects.None;
 		}
 		
 		internal void InternalDrop(DragEventArgs e, int index)
@@ -612,7 +648,9 @@ namespace ICSharpCode.TreeView
 		
 		public virtual void Drop(DragEventArgs e, int index)
 		{
-			throw new NotSupportedException(GetType().Name + " does not support Drop()");
+			// Since the default drag implementation uses Copy(),
+			// we'll use Paste() in our default drop implementation.
+			Paste(e.Data);
 		}
 		#endregion
 		

src/Libraries/SharpTreeView/ICSharpCode.TreeView/SharpTreeNodeView.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Text;
 using System.Windows.Controls;
@@ -150,8 +151,10 @@ namespace ICSharpCode.TreeView
 			else {
 				result -= 19;
 			}
-			if (result < 0)
-				throw new InvalidOperationException();
+			if (result < 0) {
+				Debug.WriteLine("Negative indent level detected for node " + Node);
+				result = 0;
+			}
 			return result;
 		}
 	}

src/Libraries/SharpTreeView/ICSharpCode.TreeView/SharpTreeView.cs

@@ -355,7 +355,7 @@ namespace ICSharpCode.TreeView
 			
 			if (Root != null && !ShowRoot) {
 				e.Handled = true;
-				Root.CanDrop(e, Root.Children.Count);
+				e.Effects = Root.GetDropEffect(e, Root.Children.Count);
 			}
 		}
 
@@ -365,7 +365,9 @@ namespace ICSharpCode.TreeView
 
 			if (Root != null && !ShowRoot) {
 				e.Handled = true;
-				Root.InternalDrop(e, Root.Children.Count);
+				e.Effects = Root.GetDropEffect(e, Root.Children.Count);
+				if (e.Effects != DragDropEffects.None)
+					Root.InternalDrop(e, Root.Children.Count);
 			}
 		}
 		
@@ -377,10 +379,12 @@ namespace ICSharpCode.TreeView
 		internal void HandleDragOver(SharpTreeViewItem item, DragEventArgs e)
 		{
 			HidePreview();
+			e.Effects = DragDropEffects.None;
 			
 			var target = GetDropTarget(item, e);
 			if (target != null) {
 				e.Handled = true;
+				e.Effects = target.Effect;
 				ShowPreview(target.Item, target.Place);
 			}
 		}
@@ -393,6 +397,7 @@ namespace ICSharpCode.TreeView
 				var target = GetDropTarget(item, e);
 				if (target != null) {
 					e.Handled = true;
+					e.Effects = target.Effect;
 					target.Node.InternalDrop(e, target.Index);
 				}
 			} catch (Exception ex) {
@@ -414,6 +419,7 @@ namespace ICSharpCode.TreeView
 			public double Y;
 			public SharpTreeNode Node;
 			public int Index;
+			public DragDropEffects Effect;
 		}
 
 		DropTarget GetDropTarget(SharpTreeViewItem item, DragEventArgs e)
@@ -485,13 +491,14 @@ namespace ICSharpCode.TreeView
 			GetNodeAndIndex(item, place, out node, out index);
 
 			if (node != null) {
-				e.Effects = DragDropEffects.None;
-				if (node.CanDrop(e, index)) {
+				var effect = node.GetDropEffect(e, index);
+				if (effect != DragDropEffects.None) {
 					DropTarget target = new DropTarget() {
 						Item = item,
 						Place = place,
 						Node = node,
-						Index = index
+						Index = index,
+						Effect = effect
 					};
 					targets.Add(target);
 				}
@@ -614,45 +621,78 @@ namespace ICSharpCode.TreeView
 
 		static void HandleExecuted_Cut(object sender, ExecutedRoutedEventArgs e)
 		{
-			
+			e.Handled = true;
+			SharpTreeView treeView = (SharpTreeView)sender;
+			var nodes = treeView.GetTopLevelSelection().ToArray();
+			if (nodes.Length > 0)
+				nodes[0].Cut(nodes);
 		}
 
 		static void HandleCanExecute_Cut(object sender, CanExecuteRoutedEventArgs e)
 		{
-			e.CanExecute = false;
+			SharpTreeView treeView = (SharpTreeView)sender;
+			var nodes = treeView.GetTopLevelSelection().ToArray();
+			e.CanExecute = nodes.Length > 0 && nodes[0].CanCut(nodes);
+			e.Handled = true;
 		}
 
 		static void HandleExecuted_Copy(object sender, ExecutedRoutedEventArgs e)
 		{
-			
+			e.Handled = true;
+			SharpTreeView treeView = (SharpTreeView)sender;
+			var nodes = treeView.GetTopLevelSelection().ToArray();
+			if (nodes.Length > 0)
+				nodes[0].Copy(nodes);
 		}
 
 		static void HandleCanExecute_Copy(object sender, CanExecuteRoutedEventArgs e)
 		{
-			e.CanExecute = false;
+			SharpTreeView treeView = (SharpTreeView)sender;
+			var nodes = treeView.GetTopLevelSelection().ToArray();
+			e.CanExecute = nodes.Length > 0 && nodes[0].CanCopy(nodes);
+			e.Handled = true;
 		}
 
 		static void HandleExecuted_Paste(object sender, ExecutedRoutedEventArgs e)
 		{
-			
+			SharpTreeView treeView = (SharpTreeView)sender;
+			var data = Clipboard.GetDataObject();
+			if (data != null) {
+				var selectedNode = (treeView.SelectedItem as SharpTreeNode) ?? treeView.Root;
+				if (selectedNode != null)
+					selectedNode.Paste(data);
+			}
+			e.Handled = true;
 		}
 
 		static void HandleCanExecute_Paste(object sender, CanExecuteRoutedEventArgs e)
 		{
-			e.CanExecute = false;
+			SharpTreeView treeView = (SharpTreeView)sender;
+			var data = Clipboard.GetDataObject();
+			if (data == null) {
+				e.CanExecute = false;
+			} else {
+				var selectedNode = (treeView.SelectedItem as SharpTreeNode) ?? treeView.Root;
+				e.CanExecute = selectedNode != null && selectedNode.CanPaste(data);
+			}
+			e.Handled = true;
 		}
 		
 		static void HandleExecuted_Delete(object sender, ExecutedRoutedEventArgs e)
 		{
+			e.Handled = true;
 			SharpTreeView treeView = (SharpTreeView)sender;
-			foreach (SharpTreeNode node in treeView.GetTopLevelSelection().ToArray())
-				node.Delete();
+			var nodes = treeView.GetTopLevelSelection().ToArray();
+			if (nodes.Length > 0)
+				nodes[0].Delete(nodes);
 		}
 
 		static void HandleCanExecute_Delete(object sender, CanExecuteRoutedEventArgs e)
 		{
 			SharpTreeView treeView = (SharpTreeView)sender;
-			e.CanExecute = treeView.GetTopLevelSelection().All(node => node.CanDelete());
+			var nodes = treeView.GetTopLevelSelection().ToArray();
+			e.CanExecute = nodes.Length > 0 && nodes[0].CanDelete(nodes);
+			e.Handled = true;
 		}
 		
 		/// <summary>

src/Libraries/SharpTreeView/ICSharpCode.TreeView/SharpTreeViewItem.cs

@@ -78,9 +78,7 @@ namespace ICSharpCode.TreeView
 				    Math.Abs(currentPoint.Y - startPoint.Y) >= SystemParameters.MinimumVerticalDragDistance) {
 
 					var selection = ParentTreeView.GetTopLevelSelection().ToArray();
-					if (Node.CanDrag(selection)) {
-						Node.StartDrag(this, selection);
-					}
+					Node.StartDrag(this, selection);
 				}
 			}
 		}