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 < 0) { 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);

       }