datagridview使用tooltip控件显示单元格内容

代码如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace Exam2
{
    public partial class MainForm : Form
    {
        private int cellColumnIndex = -1;//列索引
        private int cellRowIndex = -1;//行索引
        public MainForm()
        {
            InitializeComponent();

            //设置提示工具的相关属性值
            this.dgvUserInfo.ShowCellToolTips = false;
            this.toolTip.AutomaticDelay = 0;
            this.toolTip.OwnerDraw = true;
            this.toolTip.ShowAlways = true;
            this.toolTip.ToolTipTitle = " ";
            this.toolTip.UseAnimation = true;
            this.toolTip.UseFading = true;
        }

        /// <summary>
        /// 显示用户信息
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void MainForm_Load(object sender, EventArgs e)
        {
            string sql = "select 用户ID=userID,用户名=name,用户登录名=username,用户密码=userPassword from userInfo";
            SqlConnection conn = DBHelper.GetConnection();
            SqlDataAdapter adapter = new SqlDataAdapter(sql,conn);
            DataSet ds = new DataSet();
            adapter.Fill(ds);
            this.dgvUserInfo.DataSource = ds.Tables[0];
        }     

        private void dgvUserInfo_CellMouseLeave(object sender, DataGridViewCellEventArgs e)
        {
            this.toolTip.Hide(this.dgvUserInfo);//鼠标移出单元格后隐藏提示工具      
        }

        private void dgvUserInfo_CellMouseEnter(object sender, DataGridViewCellEventArgs e)
        {
            //判断选择单元格的有效性
            if (e.RowIndex < 0 || e.ColumnIndex < 0)
            {
                return;
            }

            this.toolTip.Hide(this.dgvUserInfo);
            this.cellColumnIndex = e.ColumnIndex;//获取列索引
            this.cellRowIndex = e.RowIndex;//获取行索引

            if (this.cellColumnIndex >= 0 && this.cellRowIndex >= 0)
            {
                Point mousePos = PointToClient(MousePosition);//获取鼠标当前的位置
                //获取鼠标移入的单元格中的值
                string tip = this.dgvUserInfo[this.cellColumnIndex, this.cellRowIndex].Value.ToString();
                this.toolTip.Show(tip, this.dgvUserInfo, mousePos);//在指定位置显示提示工具
            }                     
        }

        //绘制提示工具
        private void toolTip_Draw(object sender, DrawToolTipEventArgs e)
        {
            e.Graphics.FillRectangle(Brushes.AliceBlue, e.Bounds);
            e.Graphics.DrawRectangle(Pens.Chocolate, new Rectangle(0, 0, e.Bounds.Width - 1, e.Bounds.Height - 1));
            e.Graphics.DrawString(this.toolTip.ToolTipTitle + e.ToolTipText, e.Font, Brushes.Red, e.Bounds);
        }
    }
}