c#多选下拉框（ComboBox）

代码如下

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Drawing;
 using System.Data;
 using System.Linq;
 using System.Text;
 using System.Windows.Forms;
 using System.Collections;
 using System.Reflection;
 using Newtonsoft.Json.Linq;

 namespace ControlsAA
 {
     public class ComboBoxEx : ComboBox
     {
         TreeView lst = new TreeView();

         public ComboBoxEx()
         {
             this.DrawMode = DrawMode.OwnerDrawFixed;//只有设置这个属性为OwnerDrawFixed才可能让重画起作用
             lst.KeyUp += new KeyEventHandler(lst_KeyUp);
             lst.MouseUp += new MouseEventHandler(lst_MouseUp);
             // lst.KeyDown += new KeyEventHandler(lst_KeyDown);
             lst.Leave += new EventHandler(lst_Leave);
             lst.CheckBoxes = true;
             lst.ShowLines = false;
             lst.ShowPlusMinus = false;
             lst.ShowRootLines = false;
             this.DropDownHeight = ;
         }

         void lst_Leave(object sender, EventArgs e)
         {
             lst.Hide();
         }
         #region Property

         [Description("选定项的值"), Category("Data")]
         public List<TreeNode> SelectedItems
         {
             get
             {
                 List<TreeNode> lsttn = new List<TreeNode>();
                 foreach (TreeNode tn in lst.Nodes)
                 {
                     if (tn.Checked)
                     {
                         lsttn.Add(tn);
                     }
                 }
                 return lsttn;
             }
         }

         /// <summary>
         /// 数据源
         /// </summary>
         [Description("数据源"), Category("Data")]
         public object DataSource
         {
             get;
             set;
         }
         /// <summary>
         /// 显示字段
         /// </summary>
         [Description("显示字段"), Category("Data")]
         public string DisplayFiled
         {
             get;
             set;
         }
         /// <summary>
         /// 值字段
         /// </summary>
         [Description("值字段"), Category("Data")]
         public string ValueFiled
         {
             get;
             set;
         }
         #endregion

         public void DataBind()
         {
             this.BeginUpdate();
             if (DataSource != null)
             {
                 if (DataSource is IDataReader)
                 {
                     DataTable dataTable = new DataTable();
                     dataTable.Load(DataSource as IDataReader);

                     DataBindToDataTable(dataTable);
                 }
                 else if (DataSource is DataView || DataSource is DataSet || DataSource is DataTable)
                 {
                     DataTable dataTable = null;

                     if (DataSource is DataView)
                     {
                         dataTable = ((DataView)DataSource).ToTable();
                     }
                     else if (DataSource is DataSet)
                     {
                         dataTable = ((DataSet)DataSource).Tables[];
                     }
                     else
                     {
                         dataTable = ((DataTable)DataSource);
                     }

                     DataBindToDataTable(dataTable);
                 }
                 else if (DataSource is IEnumerable)
                 {
                     DataBindToEnumerable((IEnumerable)DataSource);
                 }
                 else
                 {
                     throw new Exception("DataSource doesn't support data type: " + DataSource.GetType().ToString());
                 }
             }
             else
             {
                 lst.Nodes.Clear();
             }

             lst.ItemHeight = this.ItemHeight;
             lst.BorderStyle = BorderStyle.FixedSingle;
             lst.Size = new Size(this.DropDownWidth, this.ItemHeight * (this.MaxDropDownItems - ) - (int)this.ItemHeight / );
             lst.Location = new Point(this.Left, this.Top + this.ItemHeight + );
             this.Parent.Controls.Add(lst);
             lst.Hide();
             this.EndUpdate();
         }

         private void DataBindToDataTable(DataTable dt)
         {
             foreach (DataRow dr in dt.Rows)
             {
                 TreeNode tn = new TreeNode();
                 if (!string.IsNullOrEmpty(DisplayFiled) && !string.IsNullOrEmpty(ValueFiled))
                 {
                     tn.Text = dr[DisplayFiled].ToString();
                     tn.Tag = dr[ValueFiled].ToString();
                 }
                 else if (string.IsNullOrEmpty(ValueFiled))
                 {
                     tn.Text = dr[DisplayFiled].ToString();
                     tn.Tag = dr[DisplayFiled].ToString();
                 }
                 else if (string.IsNullOrEmpty(DisplayFiled))
                 {
                     tn.Text = dr[ValueFiled].ToString();
                     tn.Tag = dr[ValueFiled].ToString();
                 }
                 else
                 {
                     throw new Exception("ValueFiled和DisplayFiled至少保证有一项有值");
                 }

                 tn.Checked = false;
                 lst.Nodes.Add(tn);
             }
         }

         /// <summary>
         /// 绑定到可枚举类型
         /// </summary>
         /// <param name="enumerable">可枚举类型</param>
         private void DataBindToEnumerable(IEnumerable enumerable)
         {
             IEnumerator enumerator = enumerable.GetEnumerator();
             while (enumerator.MoveNext())
             {
                 object currentObject = enumerator.Current;
                 lst.Nodes.Add(CreateListItem(currentObject));
             }
         }

         private TreeNode CreateListItem(Object obj)
         {
             TreeNode item = new TreeNode();

             if (obj is string)
             {
                 item.Text = obj.ToString();
                 item.Tag = obj.ToString();
             }
             else
             {
                 if (DisplayFiled != "")
                 {
                     item.Text = GetPropertyValue(obj, DisplayFiled);
                 }
                 else
                 {
                     item.Text = obj.ToString();
                 }

                 if (ValueFiled != "")
                 {
                     item.Tag = GetPropertyValue(obj, ValueFiled);
                 }
                 else
                 {
                     item.Tag = obj.ToString();
                 }
             }
             return item;
         }

         private string GetPropertyValue(object obj, string propertyName)
         {
             object result = null;

             result = ObjectUtil.GetPropertyValue(obj, propertyName);
             return result == null ? String.Empty : result.ToString();
         }

         #region override

         protected override void OnKeyUp(KeyEventArgs e)
         {
             base.OnKeyDown(e);
             bool Pressed = (e.Control && ((e.KeyData & Keys.A) == Keys.A));
             if (Pressed)
             {
                 this.Text = "";
                 for (int i = ; i < lst.Nodes.Count; i++)
                 {
                     lst.Nodes[i].Checked = true;
                     if (this.Text != "")
                     {
                         this.Text += ",";
                     }
                     this.Text += lst.Nodes[i].Tag;
                 }
             }
         }

         protected override void OnMouseDown(MouseEventArgs e)
         {
             this.DroppedDown = false;

         }

         protected override void OnMouseUp(MouseEventArgs e)
         {
             this.DroppedDown = false;
             lst.Focus();
         }

         protected override void OnDropDown(EventArgs e)
         {
             string strValue = this.Text;
             if (!string.IsNullOrEmpty(strValue))
             {
                 List<string> lstvalues = strValue.Split(',').ToList<string>();
                 foreach (TreeNode tn in lst.Nodes)
                 {
                     if (tn.Checked && !lstvalues.Contains(tn.Tag.ToString()) && !string.IsNullOrEmpty(tn.Tag.ToString().Trim()))
                     {
                         tn.Checked = false;
                     }
                     else if (!tn.Checked && lstvalues.Contains(tn.Tag.ToString()) && !string.IsNullOrEmpty(tn.Tag.ToString().Trim()))
                     {
                         tn.Checked = true;
                     }
                 }
             }

             lst.Show();

         }
         #endregion

         private void lst_KeyUp(object sender, KeyEventArgs e)
         {
             this.OnKeyUp(e);
         }

         private void lst_MouseUp(object sender, MouseEventArgs e)
         {
             try
             {
                 this.Text = "";
                 for (int i = ; i < lst.Nodes.Count; i++)
                 {
                     if (lst.Nodes[i].Checked)
                     {
                         if (this.Text != "")
                         {
                             this.Text += ",";
                         }
                         this.Text += lst.Nodes[i].Tag;
                     }
                 }
             }
             catch
             {
                 this.Text = "";
             }
             bool isControlPressed = (Control.ModifierKeys == Keys.Control);
             bool isShiftPressed = (Control.ModifierKeys == Keys.Shift);
             if (isControlPressed || isShiftPressed)
                 lst.Show();
             else
                 lst.Hide();
         }

     }

     /// <summary>
     /// 对象帮助类
     /// </summary>
     public class ObjectUtil
     {
         /// <summary>
         /// 获取对象的属性值
         /// </summary>
         /// <param name="obj">可能是DataRowView或一个对象</param>
         /// <param name="propertyName">属性名</param>
         /// <returns>属性值</returns>
         public static object GetPropertyValue(object obj, string propertyName)
         {
             object result = null;

             try
             {
                 if (obj is DataRow)
                 {
                     result = (obj as DataRow)[propertyName];
                 }
                 else if (obj is DataRowView)
                 {
                     result = (obj as DataRowView)[propertyName];
                 }
                 else if (obj is JObject)
                 {
                     result = (obj as JObject).Value<JValue>(propertyName).Value; //.getValue(propertyName);
                 }
                 else
                 {
                     result = GetPropertyValueFormObject(obj, propertyName);
                 }
             }
             catch (Exception)
             {
                 // 找不到此属性
             }

             return result;
         }

         /// <summary>
         /// 获取对象的属性值
         /// </summary>
         /// <param name="obj">对象</param>
         /// <param name="propertyName">属性名（"Color"、"BodyStyle"或者"Info.UserName"）</param>
         /// <returns>属性值</returns>
         private static object GetPropertyValueFormObject(object obj, string propertyName)
         {
             object rowObj = obj;
             object result = null;

             if (propertyName.IndexOf(".") > )
             {
                 string[] properties = propertyName.Split('.');
                 object tmpObj = rowObj;

                 for (int i = ; i < properties.Length; i++)
                 {
                     PropertyInfo property = tmpObj.GetType().GetProperty(properties[i], BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
                     if (property != null)
                     {
                         tmpObj = property.GetValue(tmpObj, null);
                     }
                 }

                 result = tmpObj;
             }
             else
             {
                 PropertyInfo property = rowObj.GetType().GetProperty(propertyName, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
                 if (property != null)
                 {
                     result = property.GetValue(rowObj, null);
                 }
             }

             return result;
         }
     }
 }

需要引用的文件在这里http://pan.baidu.com/s/1qXa97UO