用C#实现文件下载器（2）

导读：
　　这样，程序主体部分的代码已经完成了，不过要完成全部程序还需要一些工作。由于在程序接收网络文件数据的时候运用到了while循环体，这样会很占程序资源，表现的形式就是主窗体不能自由移动。为了解决这个问题，我们在程序中用到了多线程机制。我们在响应按钮的事件中新建一个线程，该线程就是用来实现网络文件下载功能的。如此，文件下载的线程和程序主线程并存，共享进程资源，使得程序顺畅运行。这样，我们在按钮控件的消息响应函数里添加如下代码：
　　Thread th = new Thread(new ThreadStart(StartDownload)); th.Start();
　　该线程的实现函数就是StartDownload（），而上面介绍的那些代码就是这个函数的主体部分。
　　最后，因为程序中运用到了WebRequest、WebClient、FileStream、Thread等类，所以最重要的就是在程序的开始处添加如下名字空间：
　　using System.Net; using System.IO; using System.Threading;
　　下面就是程序的源代码：
　　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.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.AddRange(new System.Windows.Forms.Control[] { this.Start, this.statusBar, this.tarAddress, this.srcAddress, this.label2, 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.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); byte[] mbyte = new byte[100000]; int allmybyte = (int)mbyte.Length; int startmbyte = 0; statusBar.Text = "正在接收数据..."; 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(); } } }
　　程序完毕，运行程序图示如下：

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