莫诺说系统.Net.Dns.GetHostEntry(字符串)由于其保护级别而不可访问

我现在正在上一节课,其中一些例子是用C#。因为我的笔记本电脑运行Linux,所以我在Ubuntu上使用的是Mono 2.6.7。

using System.Net.Sockets;
using System.Net;
using System;

/// <summary>
/// Example program showing simple TCP socket connections in C#.NET.
/// Rather than reading and writing byte arrays, this example show
/// how to use a stream reader in the client.
/// TCPSocketServer is the socket server.
/// <author>Tim Lindquist ASU Polytechnic Department of Engineering</author>
/// <version>September, 2009</version>
/// </summary>
public class TCPSocketServer {

  public static void Main (string [] args) {
    IPAddress ipAddress = Dns.GetHostEntry("localhost").AddressList[0];
    TcpListener tcpl = new TcpListener(ipAddress, 9090);
    tcpl.Start();
    Console.WriteLine("TCPSocketServer waiting for connections on 9090");
    Socket sock = tcpl.AcceptSocket();
    string msg = "Hello Client";
    Byte[] msgBytes = System.Text.Encoding.ASCII.GetBytes(msg);
    sock.Send(msgBytes, msgBytes.Length, SocketFlags.DontRoute);
    Console.WriteLine("Message-Hello Client-sent to client.");
    tcpl.Stop();
    sock.Close();
  }
}

当我编译代码时,我得到:

/home/vivin/Projects/cst420/CSSockets/src/TCPSocketServer.cs(16,31): error CS0122: `System.Net.Dns.GetHostEntry(string)' is inaccessible due to its protection level
/usr/lib/mono/gac/System/1.0.5000.0__b77a5c561934e089/System.dll (Location of the symbol related to previous error)
ompilation failed: 1 error(s), 0 warnings

我是个C#新手;这是我编译的第一个C#程序。我试着在Google上搜索,但是这个问题没有得到太多的点击。这是单声道的问题吗?