在Winfrom 中，如何实现combox 的列表自动显示ToolTip提示 ？

  //带ToolTip的combox类文件
  public class ComboBoxWithTooltip : ComboBox
     {
     //tipProperty为显示ToolTip文本的数据源的属性
         private string tipProperty;
         public string TipProperty
         {
             get { return tipProperty; }
             set
             {
                 if (tipProperty!=value)
                 {
                     tipProperty = value;
                 }
             }
         }

        private ToolTip toolTipX = new ToolTip(); 

         /// <summary>
         /// Initializes a new instance of the <see cref="ComboBoxWithTooltip"/> class.
         /// </summary>
         public ComboBoxWithTooltip()
         {
             DrawMode = DrawMode.OwnerDrawFixed;
         }

         /// <summary>
         /// Raises the <see cref="E:System.Windows.Forms.ComboBox.DrawItem"/> event.
         /// </summary>
         /// <param name="e">A <see cref="T:System.Windows.Forms.DrawItemEventArgs"/> that contains the event data.</param>
         protected override void OnDrawItem(DrawItemEventArgs e)
         {
              ; 

             // Needed gate when DropDownStyle set to DropDownList (thanks to "Andrew" remarking on my
             // StackOverflow post (stackoverflow.com/questions/680373/tooltip-for-each-items-in-a-combo-box/).
             if (e.Index < ) { return; }
             string tiptext = FilterItemOnProperty(Items[e.Index], TipProperty) as string;//从数据源Items[e.Index]的 TipProperty属性获取ToolTip文本
            string Itemtext = GetItemText(Items[e.Index]);
             e.DrawBackground();
             using (SolidBrush br = new SolidBrush(e.ForeColor))
             { e.Graphics.DrawString(Itemtext, e.Font, br, e.Bounds); }
             if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
             {
                 toolTipX.Show(tiptext, this, e.Bounds.Right, e.Bounds.Bottom);
                 //toolTip1.AutoPopDelay = 25000;
                 //toolTip1.InitialDelay = 1000;
                 //toolTip1.ReshowDelay = 0;
             }
             e.DrawFocusRectangle();
         }

         /// <summary>
         /// Raises the <see cref="E:System.Windows.Forms.ComboBox.DropDownClosed"/> event.
         /// </summary>
         /// <param name="e">An <see cref="T:System.EventArgs"/> that contains the event data.</param>
         protected override void OnDropDownClosed(EventArgs e)
         {
             toolTipX.Hide(this);
             base.OnDropDownClosed(e);
         }
     }

===================================================

上边是实现后的结果，找了好长时间，才找到，做个记录。

实现代码如下：

?

ToolTip tt = null;

       ComboBox cb = null;

       private void Form1_Load(object sender, EventArgs e)

       {

           cb = new ComboBox();

           cb.Items.Insert(0,"第一");

           cb.Items.Insert(1,"第二");

           cb.Items.Insert(2,"第三");

           cb.Items.Insert(3,"第四");

           cb.DrawMode = DrawMode.OwnerDrawFixed;

           cb.DrawItem+=new DrawItemEventHandler(cb_DrawItem);

           cb.DropDownClosed+=new EventHandler(cb_DropDownClosed);

           this.Controls.Add(cb);

           cb.SelectedIndex = 1;

           tt = new ToolTip();

           tt.SetToolTip(cb, "zj");

       }

void cb_DrawItem(object sender, System.Windows.Forms.DrawItemEventArgs e)

       {

           // 绘制背景

           e.DrawBackground();

           //绘制列表项目

           e.Graphics.DrawString(cb.Items[e.Index].ToString(), e.Font, System.Drawing.Brushes.Black, e.Bounds);

           //将高亮的列表项目的文字传递到toolTip1(之前建立ToolTip的一个实例)

           if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)

               tt.Show(cb.Items[e.Index].ToString(), cb, e.Bounds.X + e.Bounds.Width, e.Bounds.Y + e.Bounds.Height);

           e.DrawFocusRectangle();

       }

       void cb_DropDownClosed(object sender, EventArgs e)

       {

           tt.Hide(cb);

       }