用Visual C#实现文件下载

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Net;
using System.IO;
using System.Threading;
  
namespace MyGetCar
{
 ///
 /// Form1 的摘要说明。
 ///
 public class Form1 : System.Windows.Forms.Form
 {
  private System.Windows.Forms.Label label1;
  private System.Windows.Forms.Label label2;
  private System.Windows.Forms.TextBox srcAddress;
  private System.Windows.Forms.TextBox tarAddress;
  private System.Windows.Forms.StatusBar statusBar;
  private System.Windows.Forms.Button Start;
  
  private WebClient client = new WebClient();
  
   
  ///
  /// 必需的设计器变量。
  ///
  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
   //
  }
  
  ///
  /// 清理所有正在使用的资源。
  ///
  protected override void Dispose( bool disposing )
  {
   if( disposing )
   {
    if (components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose( disposing );
  }
  
  #region Windows Form Designer generated code
  ///
  /// 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。
  ///
  private void InitializeComponent()
  {
   this.label1 = new System.Windows.Forms.Label();
   this.label2 = new System.Windows.Forms.Label();
   this.srcAddress = new System.Windows.Forms.TextBox();
   this.tarAddress = new System.Windows.Forms.TextBox();
   this.statusBar = new System.Windows.Forms.StatusBar();
   this.Start = new System.Windows.Forms.Button();
   this.button1 = new System.Windows.Forms.Button();
   this.SuspendLayout();
   //
   // label1
   //
   this.label1.Location = new System.Drawing.Point(8, 32);
   this.label1.Name = "label1";
   this.label1.Size = new System.Drawing.Size(72, 23);
   this.label1.TabIndex = 0;
   this.label1.Text = "文件地址：";
   this.label1.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
   //
   // label2
   //
   this.label2.Location = new System.Drawing.Point(8, 72);
   this.label2.Name = "label2";
   this.label2.Size = new System.Drawing.Size(72, 23);
   this.label2.TabIndex = 1;
   this.label2.Text = "另存到：";
   this.label2.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
   //
   // srcAddress
   //
   this.srcAddress.Location = new System.Drawing.Point(80, 32);
   this.srcAddress.Name = "srcAddress";
   this.srcAddress.Size = new System.Drawing.Size(216, 21);
   this.srcAddress.TabIndex = 2;
   this.srcAddress.Text = "";
   //
   // tarAddress
   //
   this.tarAddress.Location = new System.Drawing.Point(80, 72);
   this.tarAddress.Name = "tarAddress";
   this.tarAddress.Size = new System.Drawing.Size(216, 21);
   this.tarAddress.TabIndex = 3;
   this.tarAddress.Text = "";
   //
   // statusBar
   //
   this.statusBar.Location = new System.Drawing.Point(0, 151);
   this.statusBar.Name = "statusBar";
   this.statusBar.Size = new System.Drawing.Size(312, 22);
   this.statusBar.TabIndex = 4;
   //
   // Start
   //
   this.Start.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
   this.Start.Location = new System.Drawing.Point(216, 112);
   this.Start.Name = "Start";
   this.Start.Size = new System.Drawing.Size(75, 24);
   this.Start.TabIndex = 5;
   this.Start.Text = "开始下载";
   this.Start.Click += new System.EventHandler(this.Start_Click);
   
   //
   // Form1
   //
   this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
   this.ClientSize = new System.Drawing.Size(312, 173);
   this.Controls.Add(this.button1);
   this.Controls.Add(this.Start);
   this.Controls.Add(this.statusBar);
   this.Controls.Add(this.tarAddress);
   this.Controls.Add(this.srcAddress);
   this.Controls.Add(this.label2);
   this.Controls.Add(this.label1);
   this.MaximizeBox = false;
   this.Name = "Form1";
   this.Text = "文件下载器";
   this.ResumeLayout(false);
  }
  #endregion
  
  ///
  /// 应用程序的主入口点。
  ///
  [STAThread]
  static void Main()
  {
   Application.Run(new Form1());
  }
  
  private void StartDownload()
  {
   Start.Enabled = false;
   string URL = srcAddress.Text;
   int n = URL.LastIndexOf("?");
   string URLAddress = URL;
   //string URLAddress = URL.Substring(0,n);
   string fileName = URL.Substring(n+1,URL.Length-n-1);
   string Dir = tarAddress.Text;
   string Path = Dir+fileName;
  
   try
   {
    WebRequest myre=WebRequest.Create(URLAddress);
   }
   catch(WebException exp)
   {
    MessageBox.Show(exp.Message,"Error");
   }
  
   try
   {
    statusBar.Text = "开始下载文件...";
    client.DownloadFile(URLAddress,fileName);
    Stream str = client.OpenRead(URLAddress);
    //StreamReader reader = new StreamReader(str); ,这句没有什么必要！个人认为
    byte[] mbyte = new byte[100000];
    int allmybyte = (int)mbyte.Length;
    int startmbyte = 0;
    statusBar.Text = "正在接收数据...";
    //写入到BYTE数组中，起缓冲作用
    while(allmybyte>0)
    {
     int m = str.Read(mbyte,startmbyte,allmybyte);
     if(m==0)
      break;
  
     startmbyte+=m;
     allmybyte-=m;
    }
  
    FileStream fstr = new FileStream(Path,FileMode.OpenOrCreate,FileAccess.Write);
    fstr.Write(mbyte,0,startmbyte);
    str.Close();
    fstr.Close();
  
    statusBar.Text = "下载完毕！";
   }
   catch(WebException exp)
   {
    MessageBox.Show(exp.Message,"Error");
    statusBar.Text = "";
   }
  
   Start.Enabled = true;
  }
  
  
  private void Start_Click(object sender, System.EventArgs e)
  {
   Thread th = new Thread(new ThreadStart(StartDownload));
   th.Start();
  }    
 }
}