C#文本文件或其他文件新内容追加

FileStream mystream = new FileStream("C:\\a.txt", FileMode.OpenOrCreate);
StreamWriter Mywriter = new StreamWriter(mystream, Encoding.Default);
string text = "";
for (int i = 0; i < axMSFlexGrid1.Rows; i++)
for (int j = 0; j < axMSFlexGrid1.Cols; j++)
text += flex.get_TextMatrix(i, j) + "\t";
Mywriter.Write(text);
Mywriter.Close();
mystream.Close();

FileStream fs = null;
string filePath = "C:\\file.txt";
Encoding encoder = Encoding.UTF8;
byte[] bytes = encoder.GetBytes("Hello World! \n\r");
try
{
fs = File.OpenWrite(filePath);
fs.Position = fs.Length;
fs.Write(bytes, 0, bytes.Length);
}
catch (Exception ex)
{
Console.WriteLine("文件打开失败{0}", ex.ToString());
}
finally
{
fs.Close();
}

StreamWriter sw=File.AppendText("c:\\Text.txt");
sw.WriteLine("13");
sw.WriteLine("22222");
sw.WriteLine("88888");
sw.Flush();
sw.Close();