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style='font-family:黑体'>类</span></h4>
<p class=MsoNormal><a FTEL=udp><span style='font-family:宋体'>可以看出，与</span><span
lang=EN-US>TcpClient </span></a><span style='font-family:宋体'>相比，</span><span
lang=EN-US>UdpClient</span><span style='font-family:宋体'>类提供了一个较小、较简单的界面。这反映出</span><span
lang=EN-US>UDP</span><span style='font-family:宋体'>协议相对简单的本质。</span><span
lang=EN-US>TCP</span><span style='font-family:宋体'>和</span><span lang=EN-US>UDP</span><span
style='font-family:宋体'>类都在后台使用套接字，但</span><span lang=EN-US>UdpClient</span><span
style='font-family:宋体'>类不包含返回网络流以读写数据的方法。相反，成员函数</span><span lang=EN-US>Send()</span><span
style='font-family:宋体'>把一个字节数组作为参数，</span><span lang=EN-US>Receive()</span><span
style='font-family:宋体'>函数则返回一个字节数组。另外，因为</span><span lang=EN-US>UDP</span><span
style='font-family:宋体'>是一个无连接的协议，所以可以指定把通信的端点，作为</span><span lang=EN-US>Send() </span><span
style='font-family:宋体'>和</span><span lang=EN-US> Receive()</span><span
style='font-family:宋体'>方法的一个参数，而不是在前面的构造函数或</span><span lang=EN-US>Connect()</span><span
style='font-family:宋体'>方法中指定。也可以在某个后续的发送或接收过程中修改端点。</span></p>
<p class=MsoNormal><span style='font-family:宋体'>下面的代码段使用</span><span
lang=EN-US>UdpClient</span><span style='font-family:宋体'>类给回应服务</span><span
lang=EN-US>(echo service)</span><span style='font-family:宋体'>发送消息。带有回应服务的服务器在端口</span><span
lang=EN-US>7</span><span style='font-family:宋体'>处接收</span><span lang=EN-US>TCP</span><span
style='font-family:宋体'>或</span><span lang=EN-US>UDP</span><span
style='font-family:宋体'>连接。回应服务值把发送给服务器的数据再发送回客户机。这个服务可用于诊断和测试，但许多系统管理员从安全的角度考虑，不启用回应服务。</span></p>
<p class=2 style='margin-top:8.15pt;margin-right:0cm;FTEL:0cm;
margin-left:21.45pt;FTEL:.0001pt;FTEL:18.45pt'><span
lang=EN-US>using System;</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>using
System.Text;</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>using
System.Net;</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>using
System.Net.Sockets;</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>namespace
Wrox.ProCSharp.InternetAccess.UdpExample</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>{</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
class Class1</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
{</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
[STAThread]</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
static void Main(string[] args)</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
{</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
UdpClient udpClient = new UdpClient();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
string sendMsg = "Hello Echo Server";</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
byte [] sendBytes = Encoding.ASCII.GetBytes(sendMsg);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
udpClient.Send(sendBytes, sendBytes.Length, "SomeEchoServer.net", 7);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
IPEndPoint endPoint = new IPEndPoint(0,0);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
byte [] rcvBytes = udpClient.Receive(ref endPoint);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
string rcvMessage = Encoding.ASCII.GetString(rcvBytes, </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
0,</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
rcvBytes.Length);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
// should print out "Hello Echo Server"</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
Console.WriteLine(rcvMessage);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
}</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
}</span></p>
<p class=2 style='margin-top:0cm;margin-right:0cm;FTEL:8.15pt;
margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>}</span></p>
<p class=MsoNormal><span lang=EN-US>Encoding.ASCII</span><span
style='font-family:宋体'>类常常用于把字符串转换为字节数组，或把字节数组转换为字符串。还要注意</span><span
lang=EN-US>IPEndPoint</span><span style='font-family:宋体'>应按引用传送给</span><span
lang=EN-US>Receive()</span><span style='font-family:宋体'>方法。</span><span
lang=EN-US>UDP</span><span style='font-family:宋体'>不是一个面向连接的协议，所以对</span><span
lang=EN-US>Receive()</span><span style='font-family:宋体'>的每次调用都会从不同的端点读取数据，</span><span
lang=EN-US>Receive()</span><span style='font-family:宋体'>会用发送主机的</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址和端口填充该参数。</span></p>
<p class=MsoNormal><span lang=EN-US>UdpClient </span><span style='font-family:
宋体'>和</span><span lang=EN-US> TcpClient</span><span style='font-family:宋体'>在最低层的类</span><span
lang=EN-US>Socket</span><span style='font-family:宋体'>上提供了一个抽象层。</span></p>
<h4 style='FTEL:21.45pt'><span lang=EN-US>5. Socket</span><span
style='font-family:黑体'>类</span></h4>
<p class=MsoNormal><a FTEL=sock><span lang=EN-US>Socket</span></a><span
style='font-family:宋体'>类提供了网络编程的最高级控制。说明该类的最简单方式是用</span><span lang=EN-US>Socket</span><span
style='font-family:宋体'>类重新编写</span><span lang=EN-US>TcpReceive</span><span
style='font-family:宋体'>应用程序。更新后的</span><span lang=EN-US>Listen()</span><span
style='font-family:宋体'>方法如下所示：</span></p>
<p class=2 style='margin-top:8.15pt;margin-right:0cm;FTEL:0cm;
margin-left:21.45pt;FTEL:.0001pt;FTEL:18.45pt'><span
lang=EN-US>public void Listen()</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>{</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
Socket listener = new Socket(AddressFamily.InterNetwork, </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
SocketType.Stream, </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
ProtocolType.Tcp);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
listener.Bind(new IPEndPoint(IPAddress.Any, 2112));</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
listener.Listen(0);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
Socket socket = listener.Accept();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
Stream netStream = new NetworkStream(socket);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
StreamReader reader = new StreamReader(netStream);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
string result = reader.ReadToEnd();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
Invoke(new UpdateDisplayDelegate(UpdateDisplay), </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
new object[] {result} ); </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
socket.Close();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
listener.Close();</span></p>
<p class=2 style='margin-top:0cm;margin-right:0cm;FTEL:8.15pt;
margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>}</span></p>
<p class=MsoNormal><span lang=EN-US>Socket</span><span style='font-family:宋体'>类需要再编写几行代码来完成相同的任务。对于初学者来说，构造函数的参数需要为使用</span><span
lang=EN-US>TCP</span><span style='font-family:宋体'>协议的流套接字指定</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>寻址模式。这些参数只是可用于</span><span
lang=EN-US>Socket</span><span style='font-family:宋体'>类的许多组合中的一个，</span><span
lang=EN-US>TcpClient</span><span style='font-family:宋体'>类会配置这些设置。接着把监听器的套接字绑定到一个端口上，开始监听传入的连接。当传入一个连接时，就可以使用</span><span
lang=EN-US>Accept()</span><span style='font-family:宋体'>方法创建一个新的套接字，来处理该连接。最后为套接字创建一个</span><span
lang=EN-US>StreamReader</span><span style='font-family:宋体'>实例，来读取传入的数据，其方式与前面的大致相同。</span></p>
<p class=MsoNormal><span lang=EN-US>Socket</span><span style='font-family:宋体'>类也包含许多方法，用于异步接收、连接、发送和接收数据。使用这些方法和回调委托的方式与前面用</span><span
lang=EN-US>WebRequest</span><span style='font-family:宋体'>类请求异步页面的方式相同。如果确实需要了解套接字的内部情况，可以使用</span><span
lang=EN-US>GetSocketOption() </span><span style='font-family:宋体'>和</span><span
lang=EN-US> SetSocketOption()</span><span style='font-family:宋体'>方法，它们允许查看和配置各种选项，包括超时、生存期和其他低级选项。</span></p>
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