public Form2()
        {
            InitializeComponent();

            XSSFWorkbook workbook = new XSSFWorkbook();

            MemoryStream msPic = new MemoryStream();

            //將圖表資料丟入 MemoryStream
            this.chart1.SaveImage(msPic, System.Windows.Forms.DataVisualization.Charting.ChartImageFormat.Png);

            //將圖片丟入workbook 並且取得他專屬的 Index
            //MemoryStream.ToArray() ==> 就是 byte[] 陣列
            //圖片就是由一組 byte[] 陣列所組成的
            int picterIdx = workbook.AddPicture(msPic.ToArray(), NPOI.SS.UserModel.PictureType.PNG);

            XSSFSheet mySheet1 = (XSSFSheet)workbook.CreateSheet("成本表");

            //取得 Sheet 用來製造圖片的物件
            XSSFDrawing patriarch=(XSSFDrawing)mySheet1.CreateDrawingPatriarch();

            //範圍是 (1,2) 到 (15,16)
            XSSFClientAnchor anchor = new XSSFClientAnchor(0, 0, 0, 0, 1,2, 15, 16);

            //設定圖片是 workbook 裡的哪張，和範圍設定
            XSSFPicture pict = (XSSFPicture)patriarch.CreatePicture(anchor, picterIdx);

            //將圖形大小設定為原來大小
            pict.Resize();

            string pathFile = "";

            if (this.folderBrowserDialog1.ShowDialog()==DialogResult.OK)
            {
                 pathFile = this.folderBrowserDialog1.SelectedPath+"\\test.xlsx";
            }

            using (var fs = new FileStream(pathFile, FileMode.Create, FileAccess.Write))
            {
                //將活頁簿寫進去指定的檔案位置
                workbook.Write(fs);
            }

        }