【C#】在datatable中添加一序号列，编号从1依次递增，并且在第一列

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/// <summary>
        /// 在DataTable中添加一序号列，编号从1依次递增
        /// </summary>
        /// <param >DataTable</param>
        /// <returns></returns>
        private DataTable AddSeriNumToDataTable(DataTable dt)
        {
            //需要返回的值
            DataTable dtNew;
            if (dt.Columns.IndexOf("序号") >= )
            {
                dtNew = dt;
            }
            else //添加一序号列,并且在第一列
            {
                int rowLength = dt.Rows.Count;
                int  colLength= dt.Columns.Count;
                DataRow[] newRows = new DataRow[rowLength];

                dtNew = new DataTable();
                //在第一列添加“序号”列
                dtNew.Columns.Add("序号");
                for (int i = ; i < colLength; i++)
                {
                    dtNew.Columns.Add(dt.Columns[i].ColumnName);
                    //复制dt中的数据
                    for (int j = ; j < rowLength; j++)
                    {
                        if (newRows[j] == null)
                            newRows[j] = dtNew.NewRow();
                        //将其他数据填充到第二列之后，因为第一列为新增的序号列
                        newRows[j][i+] = dt.Rows[j][i];
                    }
                }
                foreach (DataRow row in newRows)
                {
                    dtNew.Rows.Add(row);
                }

            }
            //对序号列填充，从1递增
            for (int i = ; i < dt.Rows.Count; i++)
            {
                dtNew.Rows[i]["序号"] = i + ;
            }

            return dtNew;           

        }