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height=115 src="31/image009.jpg"></span></p>
<p align=center style='FTEL:8.15pt'><span style='font-family:宋体'>图</span><span
lang=EN-US> 31-8</span></p>
<p class=MsoNormal><span style='font-family:宋体'>再创建一个</span><span lang=EN-US>C#
Windows</span><span style='font-family:宋体'>应用程序，其中的窗体包含两个文本框</span><span
lang=EN-US>(txtHost </span><span style='font-family:宋体'>和</span><span
lang=EN-US> txtPort)</span><span style='font-family:宋体'>，分别用于主机名和端口，该窗体还有一个按钮</span><span
lang=EN-US>(btnSend)</span><span style='font-family:宋体'>，单击它可以启动连接。首先，确保包含相关的命名空间：</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.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-top:0cm;margin-right:0cm;FTEL:8.15pt;
margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>using System.IO;</span></p>
<p class=MsoNormal><span style='font-family:宋体'>按钮的单击事件处理程序如下所示。</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>private void btnSend_Click(object sender, System.EventArgs e)</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>
TcpClient tcpClient = new TcpClient(txtHost.Text, Int32.Parse(txtPort.Text));</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
NetworkStream ns = tcpClient.GetStream();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
FileStream fs = File.Open("..\\..\\form1.cs", FileMode.Open);</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>
int data = fs.ReadByte();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
while(data != -1)</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>
ns.WriteByte((byte)data);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
data = fs.ReadByte();</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>
fs.Close(); </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
ns.Close();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
tcpClient.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 style='font-family:宋体'>这个示例用主机名和端口号创建了</span><span
lang=EN-US>TcpClient</span><span style='font-family:宋体'>。另外，如果有</span><span
lang=EN-US>IPEndPoint</span><span style='font-family:宋体'>类的一个实例，就可以把该实例传送给</span><span
lang=EN-US>TcpClient</span><span style='font-family:宋体'>构造函数。在得到</span><span
lang=EN-US>NetworkStream</span><span style='font-family:宋体'>类的一个实例后，打开源代码文件，开始读取字节。与许多二进制流一样，这里也需要将</span><span
lang=EN-US>ReadByte()</span><span style='font-family:宋体'>方法的返回值和</span><span
lang=EN-US>-1</span><span style='font-family:宋体'>相比较，以确定是否到达流的末尾。循环读取了所有的字节，并把它们发送给网络流后，就应关闭所有打开的文件、连接和流。</span></p>
<p class=MsoNormal><span style='font-family:宋体'>在连接的另一端，</span><span
lang=EN-US>TcpReceive</span><span style='font-family:宋体'>应用程序显示传输完成后接收到的文件，该应用程序如图</span><span
lang=EN-US>31-9</span><span style='font-family:宋体'>所示。</span></p>
<p align=center><span lang=EN-US><img width=429 height=328
src="31/image010.jpg"></span></p>
<p align=center style='FTEL:8.15pt'><span style='font-family:宋体'>图</span><span
lang=EN-US> 31-9</span></p>
<p class=MsoNormal><span style='font-family:宋体'>该窗体只包含一个</span><span
lang=EN-US>RichTextBox</span><span style='font-family:宋体'>控件</span><span
lang=EN-US>txtDisplay</span><span style='font-family:宋体'>。</span><span
lang=EN-US>TcpReceive</span><span style='font-family:宋体'>应用程序使用</span><span
lang=EN-US>TcpListener</span><span style='font-family:宋体'>等待进来的连接。为了避免应用程序界面的冻结，我们使用一个后台线程来等待，然后从连接中读取。因此还需要包含</span><span
lang=EN-US>System.Threading</span><span style='font-family:宋体'>命名空间：</span></p>
<p class=a6 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.Net;</span></p>
<p class=a6 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>using
System.Net.Sockets;</span></p>
<p class=a6 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>using
System.IO;</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>using
System.Threading;</span></p>
<p class=MsoNormal><span style='font-family:宋体'>在窗体的构造函数中，添加一个后台线程：</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 Form1()</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>
InitializeComponent();</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>
Thread thread = new Thread(new ThreadStart(Listen));</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
thread.Start();</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 style='font-family:宋体'>其他重要的代码如下所示。</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>
TcpListener tcpListener = new TcpListener(2112);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
tcpListener.Start();</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>
TcpClient tcpClient = tcpListener.AcceptTcpClient();</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>
NetworkStream ns = tcpClient.GetStream();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
StreamReader sr = new StreamReader(ns);</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
string result = sr.ReadToEnd();</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> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
tcpClient.Close();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>
tcpListener.Stop();</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>public
void UpdateDisplay(string text)</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>
txtDisplay.Text= text;</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>protected delegate
void UpdateDisplayDelegate(string text);</span></p>
<p class=MsoNormal><span style='font-family:宋体'>该线程在</span><span lang=EN-US>Listen()</span><span
style='font-family:宋体'>方法中开始执行，允许在不挂起界面的情况下对</span><span lang=EN-US>AcceptTcpClient()</span><span
style='font-family:宋体'>进行调<span style='letter-spacing:.1pt'>用。注意这里把端口号</span></span><span
lang=EN-US style='letter-spacing:.1pt'>2112</span><span style='font-family:
宋体;letter-spacing:.1pt'>硬编码到应用程序中，因此需要在客户应用程序中输入相同的端口号。</span></p>
<p class=MsoNormal><span style='font-family:宋体'>我们使用</span><span lang=EN-US>AccepTcpClient()</span><span
style='font-family:宋体'>返回的</span><span lang=EN-US>TcpClient</span><span
style='font-family:宋体'>对象打开一个新流，进行读取，与本章前面的示例类似，创建一个</span><span lang=EN-US>StreamReader</span><span
style='font-family:宋体'>，把进来的网络数据转换为字符串。在关闭客户机，停止监听程序前，更新窗体的文本框。我们不想从后台线程中直接访问文本框，所以使用窗体的</span><span
lang=EN-US>Invoke()</span><span style='font-family:宋体'>方法和一个委托，把得到的字符串作为</span><span
lang=EN-US>object</span><span style='font-family:宋体'>参数数组的第一个元素来传送。</span><span
lang=EN-US>Invoke()</span><span style='font-family:宋体'>方法可确保调用正确编组到线程中，以控制用户界面上的句柄。</span></p>
<h4 style='FTEL:21.45pt'><span lang=EN-US>3. TCP</span><span
style='font-family:黑体'>和</span><span lang=EN-US>UDP</span></h4>
<p class=MsoNormal><span style='font-family:宋体'>本节要介绍的另一个协议是</span><span
lang=EN-US>UDP(</span><span style='font-family:宋体'>用户数据包协议</span><span
lang=EN-US>)</span><span style='font-family:宋体'>。</span><span lang=EN-US>UDP</span><span
style='font-family:宋体'>是一个功能较少的简单协议，但其开销也很小，开发人员常常在速度和性能要求比可靠性更高的应用程序中使用</span><span
lang=EN-US>UDP</span><span style='font-family:宋体'>，例如视频流应用程序。相反，</span><span
lang=EN-US>TCP</span><span style='font-family:宋体'>提供了许多功能来确保数据的传输，它还提供了错误校正、当数据丢失或数据包被损坏时重新传输它们的功能。最后，</span><span
lang=EN-US>TCP</span><span style='font-family:宋体'>可缓存进来和出去的数据，还保证在传输过程中，在把数据包传送给应用程序之前，重新编组杂乱的一系列数据包。即使有一些额外的开销，</span><span
lang=EN-US>TCP</span><span style='font-family:宋体'>仍是在</span><span lang=EN-US>Internet</span><span
style='font-family:宋体'>上使用最广泛的协议，因为它有非常高的可靠性。</span></p>
<h4 style='FTEL:21.45pt'><span lang=EN-US>4. UDP</span><span
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