1.  读文件

//方法1
        StreamReader srFile=new StreamReader(filename,Encoding.Default);
        while(srFile.Peek() > -1) // Check EOF
        { 
 
            sql+= srFile.ReadLine(); // Read one line
        }
        srFile.Close();
        this.richTextBox1.Text=sql;
//方法2
        StreamReader sr=File.OpenText(filename);
        String input;
        while((input=sr.ReadLine())!=null)
        { 
 
            sql+=input;
        }
        sr.Close();
        this.richTextBox1.Text=sql;
//方法3
        this.richTextBox1.LoadFile(filename,RichTextBoxStreamType.PlainText);

2.  写文件

StreamWriter sw=new StreamWriter(filename);//,false);
        sw.Write(text);
         sw.Flush();//从缓冲区写入基础流(文件)
     sw.Close();