调试易

if (!File.Exists("SwitchFailure.txt"))
                    {
                        FileStream fs1 = new FileStream("SwitchFailure.txt", FileMode.Create, FileAccess.Write);//创建写入文件 
                        StreamWriter sw = new StreamWriter(fs1);
                        sw.WriteLine("DocNo:" + dt.Rows[i][1].ToString().Trim() + "\r\nDocRev:" + dt.Rows[i][2].ToString().Trim()+"\r\n---------------------\r\n");//开始写入值
                        sw.Close();
                        fs1.Close();
                    }
                    else
                    {
                        FileStream fs = new FileStream("SwitchFailure.txt", FileMode.Open, FileAccess.Write);
                        StreamWriter sr = new StreamWriter(fs);
                        sr.WriteLine("\r\nDocNo:" + dt.Rows[i][1].ToString().Trim() + "\r\nDocRev:" + dt.Rows[i][2].ToString().Trim()  + "\r\n---------------------");
                        sr.Close();
                        fs.Close();
                    }爲什麽後面寫入值就覆蓋了前面的值呢，就是只保留了最後一組值。求高手解答。