C#读写TXT文件

/// <summary>
/// 读写TXT文件
/// </summary>
public void WritTxt(string FileName)
{
string OldStr = "";
try
{
//读取文件
OldStr = File.ReadAllText( FileName, Encoding.UTF8);
}
catch (Exception)
{
}
try
{
StringBuilder SB = new StringBuilder();
FileStream F1 = new FileStream(FileName, FileMode.Create);
if (OldStr != string.Empty)
{
SB.Append(OldStr);
}
for (int i = 0; i < 100; i++)
{
SB.Append("这是第" + i.ToString() + "行" + "\r\n");
}
byte[] Wri = System.Text.Encoding.UTF8.GetBytes(SB.ToString());
F1.Write(Wri, 0, Wri.Length);
F1.Close();

}
catch (Exception)
{

}

}