树节点的拖动

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
namespace DropTree
...{
    public abstract class BaseTree : TreeView
    ...{
        private bool droping;
        private const string NODE_TYPE = "System.Windows.Forms.TreeNode";
        private string nodeType;

        protected BaseTree()
            : base()
        ...{
            AllowDrop = true;
            ItemDrag += new ItemDragEventHandler(BaseTree_ItemDrag);
            DragEnter += new DragEventHandler(BaseTree_DragEnter);
            DragOver += new DragEventHandler(BaseTree_DragOver);
            DragDrop += new DragEventHandler(BaseTree_DragDrop);
            AfterSelect += new System.Windows.Forms.TreeViewEventHandler(BaseTree_AfterSelect);
            nodeType = NODE_TYPE;
        }

        /**//// <summary>
        /// 如果重写树节点,请重新为此属性赋值.格式:命名空间.类名
        /// </summary>
        public string NodeType
        ...{
            get ...{ return nodeType; }
            set
            ...{
                if (string.IsNullOrEmpty(value))
                    nodeType = NODE_TYPE;
                else
                    nodeType = value;
            }
        }

        /**//// <summary>
        /// 选中节点后的操作
        /// </summary>
        protected abstract void AfterSelectedNode();

        /**//// <summary>
        /// 移动后的操作
        /// </summary>
        /// <param name="parentNode">目标节点</param>
        /// <param name="dropNode">移动节点</param>
        protected abstract void MoveNode(TreeNode parentNode, TreeNode dropNode);

        /**//// <summary>
        /// 检查当前移动节点是否能移动到该目标节点下,移动提示对话框也可在此操作
        /// </summary>
        /// <param name="parentNode">目标节点</param>
        /// <param name="dropNode">移动节点</param>
        /// <returns>如果允许</returns>
        protected abstract bool AllowMove(TreeNode parentNode, TreeNode dropNode);

        private void BaseTree_DragDrop(object sender, DragEventArgs e)
        ...{
            this.droping = true;
            if (!e.Data.GetDataPresent(nodeType, true))
                this.droping = false;
            else
            ...{

                TreeNode dropNode = (TreeNode)e.Data.GetData(nodeType);
                TreeNode parentNode = SelectedNode;
                if ((e.Effect != DragDropEffects.Copy) && (parentNode != null) && AllowMove(parentNode, dropNode))
                ...{
                    MoveNode(parentNode, dropNode);
                    dropNode.Remove();
                    parentNode.Nodes.Add(dropNode);
                    parentNode.Expand();
                    SelectedNode = dropNode;
                }
                this.droping = false;
            }
        }

        private void BaseTree_DragEnter(object sender, DragEventArgs e)
        ...{
            if (e.Data.GetDataPresent(nodeType, true))
            ...{
                if (((e.KeyState & 8) == 8) & ((e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy))
                ...{
                    e.Effect = DragDropEffects.Copy;
                }
                else
                ...{
                    e.Effect = DragDropEffects.Move;
                }
            }
            else
            ...{
                e.Effect = DragDropEffects.None;
            }
        }

        private void BaseTree_DragOver(object sender, DragEventArgs e)
        ...{
            this.droping = true;
            if (!e.Data.GetDataPresent(nodeType, true))
            ...{
                this.droping = false;
            }
            else
            ...{
                Point point = PointToClient(new Point(e.X, e.Y));
                TreeNode targetNode = this.GetNodeAt(point);
                SelectedNode = targetNode;
                TreeNode dropNode = (TreeNode)e.Data.GetData(nodeType);
                if (targetNode == null)
                ...{
                    e.Effect = DragDropEffects.None;
                    this.droping = false;
                }
                else
                ...{
                    while (targetNode != null)
                    ...{
                        if (targetNode == dropNode || dropNode.Parent == SelectedNode)
                        ...{
                            e.Effect = DragDropEffects.None;
                            this.droping = false;
                            return;
                        }
                        targetNode = targetNode.Parent;
                    }
                    if (((e.KeyState & 8) == 8) & ((e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy))
                    ...{
                        e.Effect = DragDropEffects.Copy;
                    }
                    else
                    ...{
                        e.Effect = DragDropEffects.Move;
                    }
                    this.droping = false;
                }
            }
        }

        private void BaseTree_ItemDrag(object sender, ItemDragEventArgs e)
        ...{
            if (e.Button == MouseButtons.Left)
            ...{
                this.droping = true;
                this.DoDragDrop(e.Item, DragDropEffects.Move);
                this.droping = false;
            }
        }

        private void BaseTree_AfterSelect(object sender, TreeViewEventArgs e)
        ...{
            if (droping == true)//在节点拖放时,跳过选中节点后的操作
                return;
            else
                AfterSelectedNode();
        }
    }

    public class TestTree:BaseTree...{
        public TestTree() : base() ...{ }
        protected override void AfterSelectedNode()
        ...{
            MessageBox.Show(SelectedNode.Text,string.Empty,
                MessageBoxButtons.OK,MessageBoxIcon.Information,
                MessageBoxDefaultButton.Button1, 0);
        }

        protected override void MoveNode(TreeNode parentNode, TreeNode dropNode)
        ...{
            //throw new Exception("The method or operation is not implemented.");
        }

        protected override bool AllowMove(TreeNode parentNode, TreeNode dropNode)
        ...{
            return true;
        }
    }
}