private void Form1_Load(object sender, EventArgs e)
        {
            //connStr = connPath1 + conn2;
            fileName = connPath1 + conn2; 
            connStr = "Provider= Microsoft.Ace.OLEDB.12.0;Data Source =" + connPath1 + conn2; ;

            chart1.MouseHover += new EventHandler(chart1_MouseHover);  

        }

        //直接用鼠标悬停事件处理
        void chart1_MouseHover(object sender, EventArgs e)
        {
            if (chart1.Series.Count != 0)//这里判断是否包含Series，也可以用Series.Contains()  
            {
                for (int i = 0; i < chart1.Series["Series1"].Points.Count; i++)
                {
                    chart1.Series["Series1"].Points[i].ToolTip = "#VAL";//获取值，可以酌量添加  
                }
            }

        }      

            //在显示工具提示之前发生以获取工具提示文本
            chart1.GetToolTipText += new EventHandler<ToolTipEventArgs>(chart_GetToolTipText);  
        void chart_GetToolTipText(object sender, ToolTipEventArgs e)
        {
            if (e.HitTestResult.ChartElementType == ChartElementType.DataPoint)
            {
                int i = e.HitTestResult.PointIndex;
                DataPoint dp = e.HitTestResult.Series.Points[i];
                //分别显示x轴和y轴的数值，其中{1:F3},表示显示的是float类型，精确到小数点后3位。  
                e.Text = string.Format("次数:{0};数值:{1:F3} ", dp.XValue, dp.YValues[0]);
            }

        }