三．网页下载器实例介绍：

　　最后，我就综合以上.NET网络编程的一些知识，向大家展示一个很好的实例。该实例是一个运用Socket的基于同步模式的客户端应用程序，它首先通过解析服务器的IP地址建立一个终结点，同时创建一个基于流套接字的Socket连接，其运用的协议是TCP协议。通过该Socket就可以发送获取网页的命令，再通过该Socket获得服务器上默认的网页，最后通过文件流将获得的数据写入本机文件。这样就完成了网页的下载工作了

程序的代码如下：

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.IO;

namespace SocketSample
{
/// <summary>
/// Form1 的摘要说明。
/// </summary>

public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.Label label1;
private System.Windows.Forms.Label label2;
private System.Windows.Forms.Button Download;
private System.Windows.Forms.TextBox ServerAddress;
private System.Windows.Forms.TextBox Filename;
/// <summary>
/// 必需的设计器变量。
/// </summary>
private System.ComponentModel.Container
components = null;
public Form1()
{
//
// Windows 窗体设计器支持所必需的
//
InitializeComponent();

//
// TODO: 在 InitializeComponent
// 调用后添加任何构造函数代码
}

/// <summary>
/// 清理所有正在使用的资源。
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows Form Designer generated code
/// <summary>
/// 设计器支持所需的方法 - 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.label1 = new System.Windows.
Forms.Label();
this.label2 = new System.Windows.
Forms.Label();
this.Download = new System.Windows.
Forms.Button();
this.ServerAddress = new System.Windows.
Forms.TextBox();
this.Filename = new System.Windows.
Forms.TextBox();
this.SuspendLayout();
//
// label1
//
this.label1.Location = new System.Drawing.
Point(16, 24);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.
Size(80, 23);
this.label1.TabIndex = 0;
this.label1.Text = "服务器地址：";
this.label1.TextAlign = System.Drawing.
ContentAlignment.MiddleRight;
//
// label2
//
this.label2.Location = new System.Drawing.
Point(16, 64);
this.label2.Name = "label2";
this.label2.Size = new System.Drawing.
Size(80, 23);
this.label2.TabIndex = 1;
this.label2.Text = "本地文件名：";
this.label2.TextAlign = System.Drawing.
ContentAlignment.MiddleRight;
//
// Download
//
this.Download.Location = new System.
Drawing.Point(288, 24);
this.Download.Name = "Download";
this.Download.TabIndex = 2;
this.Download.Text = "开始下载";
this.Download.Click += new System.
EventHandler(this.Download_Click);
//
// ServerAddress
//
this.ServerAddress.Location = new System.
Drawing.Point(96, 24);
this.ServerAddress.Name = "ServerAddress";
this.ServerAddress.Size = new System.
Drawing.Size(176, 21);
this.ServerAddress.TabIndex = 3;
this.ServerAddress.Text = "";
//
// Filename
//
this.Filename.Location = new System.
Drawing.Point(96, 64);
this.Filename.Name = "Filename";
this.Filename.Size = new System.
Drawing.Size(176, 21);
this.Filename.TabIndex = 4;
this.Filename.Text = "";
//
// Form1
//
this.AutoScaleBaseSize = new System.
Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.
Size(376, 117);
this.Controls.AddRange(new System.Windows.
Forms.Control[] {
this.Filename,
this.ServerAddress,
this.Download,
this.label2,
this.label1}