如何找到DataGridView中的最后一行并将其写入文本文件

 List<string> lstContents = new List<string>();
        foreach (DataGridViewCell cell in mydataGrid.Rows[mydataGrid.RowCount - 1].Cells)
        {
            lstContents .Add((string)cell.Value);
        }
 string myData= string.Join(",", lstContents.ToArray());

using (StreamWriter sw = new StreamWriter(FilePath, true))
        {
            sw.WriteLine(myData);
        }