C#读写TXT文件

读TXT：

txtpath = System.AppDomain.CurrentDomain.BaseDirectory.ToString() + "test.txt";
if (File.Exists(txtpath))
{
　　StreamReader sr = new StreamReader(txtpath, Encoding.UTF8);
　　String line;
　　while ((line = sr.ReadLine()) != null)
　　{
　　　　this.textBox3.Text = line;
　　}
　　sr.Close();
}

写TXT：

txtpath = System.AppDomain.CurrentDomain.BaseDirectory.ToString() + "test.txt";if (File.Exists(txtpath))
{
    FileStream stream2 = File.Open(txtpath, FileMode.OpenOrCreate, FileAccess.Write);
    stream2.Seek(0, SeekOrigin.Begin);
    stream2.SetLength(0); //清空txt文件
    StreamWriter sw = new StreamWriter(stream2);
    sw.Write(this.textBox4.Text.ToString());
    sw.Flush();
    sw.Close();
    stream2.Close();
}
else
{
    FileStream fs = new FileStream(txtpath, FileMode.CreateNew);
    StreamWriter sw = new StreamWriter(fs);
    sw.Write(this.textBox4.Text.ToString());
    sw.Flush();
    sw.Close();
    fs.Close();
}