C# 4 and .NET 4

660 ❘ ChaPTer 24 netwOrkinG
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Windows.Forms;
Inside the form’s constructor, you spin up a background thread:
public Form1()
{
InitializeComponent();
Thread thread = new Thread(new ThreadStart(Listen));
thread.Start();
}
The remaining important code is this:
public void Listen()
{
IPAddress localAddr = IPAddress.Parse("127.0.0.1");
Int32 port = 2112;
TcpListener tcpListener = new TcpListener(localAddr, port);
tcpListener.Start();
TcpClient tcpClient = tcpListener.AcceptTcpClient();
}
NetworkStream ns = tcpClient.GetStream();
StreamReader sr = new StreamReader(ns);
string result = sr.ReadToEnd();
Invoke(new UpdateDisplayDelegate(UpdateDisplay),new object[] {result} );
tcpClient.Close();
tcpListener.Stop();
public void UpdateDisplay(string text)
{
txtDisplay.Text= text;
}
protected delegate void UpdateDisplayDelegate(string text);
The thread begins execution in the Listen() method and allows you to make the blocking call to
AcceptTcpClient() without halting the interface. Notice that the IP address (127.0.0.1) and the port
number (2112) are hard-coded into the application, so you will need to enter the same port number from the
client application.
You use the TcpClient object returned by AcceptTcpClient() to open a new stream for reading. As with
the earlier example, you create a StreamReader to convert the incoming network data into a string. Before
you close the client and stop the listener, you update the form’s text box. You do not want to access the text
box directly from your background thread, so you use the form’s Invoke() method with a delegate and pass
the result string as the first element in an array of object parameters. Invoke() ensures that your call is
correctly marshaled into the thread that owns the control handles in the user interface.
TCP Versus udP
The other protocol covered in this section is UDP (User Datagram Protocol). UDP is a simple protocol with
few features and little overhead. Developers often use UDP in applications where the speed and performance
requirements outweigh the reliability needs, for example, video streaming. In contrast, TCP offers a
number of features to confirm the delivery of data. TCP provides error correction and retransmission in
the case of lost or corrupted packets. Last, but hardly least, TCP buffers incoming and outgoing data and
also guarantees that a sequence of packets scrambled in transmission is reassembled before delivery to the
application. Even with the extra overhead, TCP is the most widely used protocol across the Internet because
of its high reliability.
www.it-ebooks.info