C# - TreeView Drag&Drop

using System;
using System.Drawing;
using System.Windows.Forms;

namespace TreeView_DragDrop
{
	public partial class Form1 : Form
	{
		private bool _dragdropCopy = false;
		private DragEventArgs _dragEventArgs;
		private MouseButtons _mouseButton;
		//---------------------------------------------------------------------
		#region Form-Events
		public Form1()
		{
			InitializeComponent();
		}
		//---------------------------------------------------------------------
		private void Form1_Load(object sender, EventArgs e)
		{
			treeView1.ExpandAll();
		}
		#endregion
		//---------------------------------------------------------------------
		/// <summary>
		/// Beginnt den DragDrop-Vorgang
		/// </summary>
		/// <param name="sender"></param>
		/// <param name="e"></param>
		private void treeView1_ItemDrag(object sender, ItemDragEventArgs e)
		{
			// Zu verschiebenden Knoten wählen:
			TreeNode sourceNode = (TreeNode)e.Item;

			_mouseButton = e.Button;

			// DragDrop beginnen:
			DoDragDrop(
				sourceNode,
				DragDropEffects.Move | DragDropEffects.Copy);
		}
		//---------------------------------------------------------------------
		/// <summary>
		/// Validiert ob der DragDrop-Vorgang zugelassen wird
		/// </summary>
		/// <param name="sender"></param>
		/// <param name="e"></param>
		private void treeView1_DragEnter(object sender, DragEventArgs e)
		{
			// Nur TreeNodes werden zugelassen:
			if (e.Data.GetDataPresent(typeof(TreeNode)))
			{
				// Strg-Taste gedrück? Prüfung über Bitmaske:
				if ((e.KeyState & 8) == 8)
					e.Effect = DragDropEffects.Copy;
				// nur linke Maustaste
				else
					e.Effect = DragDropEffects.Move;
			}
			else
				e.Effect = DragDropEffects.None;
		}
		//---------------------------------------------------------------------
		/// <summary>
		/// Verschiebt den Knoten
		/// </summary>
		/// <param name="sender"></param>
		/// <param name="e"></param>
		private void treeView1_DragDrop(object sender, DragEventArgs e)
		{
			_dragEventArgs = e;

			// Behandlung von Verschieben oder Kopieren:
			if (_mouseButton == MouseButtons.Right)
			{
				ctxDragDropKopieren.Visible =
					((e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy);
				ctxDragDropVerschieben.Visible =
					((e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move);
				ctxDragDrop.Show(e.X, e.Y);
			}
			else
			{
				_dragdropCopy = (e.Effect == DragDropEffects.Copy);
				TreeViewDragDropVerarbeiten();
			}
		}
		//---------------------------------------------------------------------
		private void ctxDragDropKopieren_Click(object sender, EventArgs e)
		{
			_dragdropCopy = true;
			TreeViewDragDropVerarbeiten();
		}
		//---------------------------------------------------------------------
		private void ctxDragDropVerschieben_Click(object sender, EventArgs e)
		{
			_dragdropCopy = false;
			TreeViewDragDropVerarbeiten();
		}
		//---------------------------------------------------------------------
		private void TreeViewDragDropVerarbeiten()
		{
			TreeNode sourceNode =
				_dragEventArgs.Data.GetData(typeof(TreeNode)) as TreeNode;

			// Knoten ermitteln dem der gedragte Knoten hinzugefügt werden 
			// soll:
			Point p = treeView1.PointToClient(new Point(
				_dragEventArgs.X,
				_dragEventArgs.Y));
			TreeNode targetNode = treeView1.GetNodeAt(p);

			if (targetNode != null)
			{
				TreeNode newNode = (TreeNode)sourceNode.Clone();

				// Hinzufügen des neuen Knotens:
				targetNode.Nodes.Add(newNode);

				// Verschieben oder Kopieren?
				if (!_dragdropCopy)				// Verschieben
					sourceNode.Remove();

				// Neuzeichnen des TreeView:
				treeView1.Invalidate();
				treeView1.ExpandAll();
			}
		}
	}
}