如下方法我插入值之后Excel报表数据全没了只剩下一个我插入的值。。。

private bool SaveDataTableToExcel(string filePath)
        {
            Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.ApplicationClass();
            try
            {
                app.Visible = false;
                Workbook wBook = app.Workbooks.Add(true);
                Worksheet wSheet = wBook.Worksheets[1] as Worksheet;

                string str = "333";
                wSheet.Cells[11, 9] = str;
                  //设置禁止弹出保存和覆盖的询问提示框   
                app.DisplayAlerts = false;
                app.AlertBeforeOverwriting = false;
                //保存工作簿   
                wBook.Save();
                //保存excel文件   
                app.Save(filePath);
                app.SaveWorkspace(filePath);
                app.Quit();
                app = null;
                return true;
            }
            catch (Exception err)
            {
                MessageBox.Show("导出Excel出错！错误原因：" + err.Message, "提示信息",
                    MessageBoxButtons.OK, MessageBoxIcon.Information);
                return false;
            }
            finally
            {
            }
        }