.NET开发：用C# Builder实现文件下载

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用C# Builder实现文件下载

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作者：徐长友

一．概述：
  　　本文通过一个实例向大家介绍用C# Builder进行Internet通讯编程的一些基本知识。我们知道.Net类包含了请求/响应层、应用协议层、传输层等层次。在本程序中，我们运用了位于请求/响应层的WebRequest类以及WebClient类等来实现高抽象程度的Internet通讯服务。本程序的功能是完成文件的下载。
二．实现原理：
  　　程序实现的原理比较简单，主要用到了WebClient类和FileStream类。其中WebClient类处于System.Net名字空间中，该类的主要功能是提供向URI标识的资源发送数据和从URI标识的资源接收数据的公共方法。我们利用其中的DownFile()方法将文件下载到本地。然后用FileStream类的实例对象以数据流的方式将文件数据写入本地文件。这样就完成了文件的下载。
三．实现步骤：
    1.首先，打开C# Builder，File->New->C# Application，Name这里我们设为"download"。
    2.主界界的设置。text设为“文件下载”,StartPosition设为CenterScreen,MaximizeBox设为False,我们在主窗体上添加如下控件：两个标签控件label1,label2、一个文本框控件textBox1、一个按钮控件button1以及一个进度条控件progressBar1。
    label1：text为URL;Label2：text为下载进度;textBox1:text设为空;button1：text设为下载;
    3.程序的编码
     //过程downfile，用于完成文件的下载
  private void downfile()
  {
   string FileName;
   WebClient DownFile=new WebClient();
   long fbytes;
   if (textBox1.Text!="")
   {
     saveFileDialog1.ShowDialog();
     FileName=saveFileDialog1.FileName;
     if(FileName!= "")
     {
      //取得文件大小
      WebRequest wr_request=WebRequest.Create(textBox1.Text);
      WebResponse wr_response=wr_request.GetResponse();
      fbytes=wr_response.ContentLength;
      progressBar1.Maximum=(int)fbytes;
      progressBar1.Step=1;
      wr_response.Close();
                           //开始下载数据
      DownFile.DownloadData(textBox1.Text);
      Stream strm = DownFile.OpenRead(textBox1.Text);
      StreamReader reader = new StreamReader(strm);
      byte[] mbyte = new byte[fbytes];
      int allmybyte = (int)mbyte.Length;
      int startmbyte = 0;
      while(fbytes>0)
      {
     int m = strm.Read(mbyte,startmbyte,allmybyte);
     if(m==0) break;
     startmbyte+=m;
     allmybyte-=m;
     progressBar1.value+=m;
      }
      FileStream fstrm = new FileStream(FileName,FileMode.OpenOrCreate,FileAccess.Write);
      fstrm.Write(mbyte,0,startmbyte);
      strm.Close();
      fstrm.Close();
      progressBar1.value=progressBar1.Maximum;
     }
   } else
   {
      MessageBox.Show("没有输入要下载的文件！");
   }
  }

     //双击“下载”按钮，输入以下代码：
     Thread th = new Thread(new ThreadStart(downfile));
     th.Start();

      //完整的代码如下：
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Net;
using System.IO;
using System.Threading;

namespace download
{
/// <summary>
/// Summary description for WinForm.
/// </summary>
public class WinForm : System.Windows.Forms.Form
{
  /// <summary>
  /// Required designer variable.
  /// </summary>
  private System.ComponentModel.Container components = null;
  private System.Windows.Forms.Label label1;
  private System.Windows.Forms.TextBox textBox1;
  private System.Windows.Forms.Button button1;
  private System.Windows.Forms.SaveFileDialog saveFileDialog1;
  private System.Windows.Forms.Label label2;
  private System.Windows.Forms.ProgressBar progressBar1;

  public WinForm()
  {
   //
   // Required for Windows Form Designer support
   //
   InitializeComponent();

   //
   // TODO: Add any constructor code after InitializeComponent call
   //
  }

  /// <summary>
  /// Clean up any resources being used.
  /// </summary>
  protected override void Dispose (bool disposing)
  {
   if (disposing)
   {
    if (components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose(disposing);
  }

  #region Windows Form Designer generated code
  /// <summary>
  /// Required method for Designer support - do not modify
  /// the contents of this method with the code editor.
  /// </summary>
  private void InitializeComponent()
  {
   this.label1 = new System.Windows.Forms.Label();
   this.textBox1 = new System.Windows.Forms.TextBox();
   this.button1 = new System.Windows.Forms.Button();
   this.saveFileDialog1 = new System.Windows.Forms.SaveFileDialog();
   this.label2 = new System.Windows.Forms.Label();
   this.progressBar1 = new System.Windows.Forms.ProgressBar();
   this.SuspendLayout();
   //
   // label1
   //
   this.label1.Location = new System.Drawing.Point(40, 40);
   this.label1.Name = "label1";
   this.label1.Size = new System.Drawing.Size(40, 16);
   this.label1.TabIndex = 0;
   this.label1.Text = "URL：";
   //
   // textBox1
   //
   this.textBox1.Location = new System.Drawing.Point(72, 36);
   this.textBox1.Name = "textBox1";
   this.textBox1.Size = new System.Drawing.Size(256, 21);
   this.textBox1.TabIndex = 1;
   this.textBox1.Text = "";
   //
   // button1
   //
   this.button1.Location = new System.Drawing.Point(256, 120);
   this.button1.Name = "button1";
   this.button1.TabIndex = 2;
   this.button1.Text = "下载";
   this.button1.Click += new System.EventHandler(this.button1_Click);
   //
   // label2
   //
   this.label2.Location = new System.Drawing.Point(8, 80);
   this.label2.Name = "label2";
   this.label2.Size = new System.Drawing.Size(72, 23);
   this.label2.TabIndex = 3;
   this.label2.Text = "下载进度：";
   //
   // progressBar1
   //
   this.progressBar1.Location = new System.Drawing.Point(72, 80);
   this.progressBar1.Name = "progressBar1";
   this.progressBar1.Size = new System.Drawing.Size(256, 16);
   this.progressBar1.TabIndex = 4;
   //
   // WinForm
   //
   this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
   this.ClientSize = new System.Drawing.Size(360, 173);
   this.Controls.Add(this.progressBar1);
   this.Controls.Add(this.label2);
   this.Controls.Add(this.button1);
   this.Controls.Add(this.textBox1);
   this.Controls.Add(this.label1);
   this.MaximizeBox = false;
   this.Name = "WinForm";
   this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
   this.Text = "文件下载";
   this.ResumeLayout(false);
  }
  #endregion

  /// <summary>
  /// The main entry point for the application.
  /// </summary>
  [STAThread]
  static void Main()
  {
   Application.Run(new WinForm());
  }

  private void downfile()
  {
   string FileName;
   WebClient DownFile=new WebClient();
   long fbytes;
   if (textBox1.Text!="")
   {
     saveFileDialog1.ShowDialog();
     FileName=saveFileDialog1.FileName;
     if(FileName!= "")
     {
      //取得文件大小
      WebRequest wr_request=WebRequest.Create(textBox1.Text);
      WebResponse wr_response=wr_request.GetResponse();
      fbytes=wr_response.ContentLength;
      progressBar1.Maximum=(int)fbytes;
      progressBar1.Step=1;
      wr_response.Close();
      //开始下载数据
      DownFile.DownloadData(textBox1.Text);
      Stream strm = DownFile.OpenRead(textBox1.Text);
      StreamReader reader = new StreamReader(strm);
      byte[] mbyte = new byte[fbytes];
      int allmybyte = (int)mbyte.Length;
      int startmbyte = 0;
      while(fbytes>0)
      {
     int m = strm.Read(mbyte,startmbyte,allmybyte);
     if(m==0) break;
     startmbyte+=m;
     allmybyte-=m;
     progressBar1.value+=m;
      }
      FileStream fstrm = new FileStream(FileName,FileMode.OpenOrCreate,FileAccess.Write);
      fstrm.Write(mbyte,0,startmbyte);
      strm.Close();
      fstrm.Close();
      progressBar1.value=progressBar1.Maximum;
     }
   } else
   {
      MessageBox.Show("没有输入要下载的文件！");
   }
  }
  private void button1_Click(object sender, System.EventArgs e)
  {
     Thread th = new Thread(new ThreadStart(downfile));
     th.Start();
  }
}
}

         4.按F9运行程序，输入一下载地址，点“下载”按钮试试。

四．结束语：
  　　以上用一个简单的例子向大家展示了如何用C# Builder实现文件的下载，我们不难发现用C# Builder进行Internet通讯编程是非常方便的。在上面的程序中，我们仅仅用到了WebClient类的一些方法，而WebClient类不只是提供了文件下载的方法，还提供了文件上传等方法，有兴趣的读者不妨自己试试，查查帮助。
      程序中使用了多线程，这是因为WebClient类占有的资源校大，在下载文件会使整个窗口的显示不完整。如果不用多线程的话，下载文件的时候，你根本没法移动窗口或进行其它的一些操作。
      有兴趣的朋友可以到我的主页下载源码 http://yousoft.hi.com.cn

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