System.IO 命名空间中经常使用的类.

File类，FileInfo，StreamReader类，StreamWriter类.下面就写一读写文本个小例子。

 1。通过FileStream 中的read方法来读。

   private void Form1_Load(object sender, EventArgs e)
        {
            FileInfo fl = new FileInfo(Application.StartupPath + @"/test.txt");
            using (FileStream fs = fl.OpenRead())
            {
                byte[] byt = new byte[fl.Length];
                fs.Read(byt, 0, byt.Length);
                fs.Close();
                this.textBox1.Text = System.Text.Encoding.Default.GetString(byt);

            }

        }

2.通过FileStream中的Write方法来写。

   private void button1_Click(object sender, EventArgs e)
        {
            FileInfo fl = new FileInfo(Application.StartupPath + @"/test.txt");
            using(FileStream fs=File.Open(Application.StartupPath+@"/test.txt",FileMode.Append))
            {
                byte []byt=System.Text.Encoding.Default.GetBytes(this.textBox1.Text);
                fs.Write(byt, 0, byt.Length);
                fs.Close();
           
            }
        }

3.通过StreamReader类中的ReadtoEnd()方法来读。

FileStream fl=File.Open(Application.StartupPath+@"/test.txt",FileMode.Open)

using(StreamReader sr=new StreamReader(fl,Encoding.Default))

{

this.TextBox1.Text=sr.ReadtoEnd();

}

4.通过StreamWriter类中的Write和WriteLine来写。

 private void button1_Click(object sender, EventArgs e)
        {
            FileInfo fs = new FileInfo(Application.StartupPath + @"/test.txt");
            using (StreamWriter sw = fs.CreateText())
            {
                sw.Write("fdsa");
            }
      }