Excel导入DataSet （winform）

 private void btnSelectFile_Click(object sender, EventArgs e)
        {
            dictionary.Clear();
            dtAll.Clear();
            //打开文件对话框。
            OpenFileDialog openFile = new OpenFileDialog();
            openFile.Multiselect = true;
            //后缀名。
            openFile.Filter = "Excel文件(*.xls,*.xlsx)|*.xls;*.xlsx";
            if (openFile.ShowDialog() == DialogResult.OK)
            {
                btnExport.Text = "导入";
                btnExport.Enabled = true;
                try
                {
                    //文件名包含路径
                    string[] filenames = openFile.FileNames;

                    for (int i = 0; i < filenames.Length; i++)
                    {
                        string filename = filenames[i];
                        //sql语句
                        string sql = "select * from [Sheet1$]";
                        //数据库连接字符串
                        string connStr = "Provider=Microsoft.Jet.OLEDB.4.0;Extended Properties=Excel 8.0;data source=" + filename;
                        //如果是2007格式
                        if (filename.ToUpper().EndsWith("XLSX"))
                        {
                            connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Extended Properties=Excel 12.0;data source=" + filename;
                        }
                        DataTable dt = SqlHelper.ExecuteDataset(connStr, sql, CommandType.Text).Tables[0];
                        string filename2 = filename.Substring(filename.LastIndexOf('\\') + 1);
                        dictionary.Add(filename2, dt);
                        if (i == 0)
                        {
                            dtAll = dt.Copy();
                        }
                        else
                        {
                            foreach (DataRow dr in dt.Rows)
                            {
                                dtAll.ImportRow(dr);
                            }
                        }
                    }
                    string filenames2 = string.Empty;
                    foreach (var key in dictionary.Keys)
                    {
                        filenames2 += key + "，";
                    }

                    txtExcelName.Text = filenames2;
                    dgvCurrent.DataSource = dtAll.DefaultView;
                    lblcount.Text = dtAll.Rows.Count.ToString();
                }
                catch (Exception err)
                {
                    MessageBox.Show("错误：" + err.Message);
                }
            }
            else
            {
                txtExcelName.Text = string.Empty;
                btnExport.Enabled = false;
            }
        }