C# NetWork Programming里面一个例子，通过异步的方式解析域名。主要是应用Dns类的BeginResolve()，和EndResolve()方法。此例子有一个问题就是当碰到解析不出来的域名时，不会调用AsyncCallback指定的函数。我加了几句代码，设定2秒钟超时时间，超时的话，显示超时。现在的问题是，超时后并没有结束域名的解析。超过2秒钟解析出的域名还会显示到listBox中。而超时后想调用Dns.EndResolve()结束解析的话会抛出异常。

有待研究。

using System;

using System.Drawing;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

using System.Data;

using System.Net;

using System.Threading;

namespace NetWork

{

public class DnsResolver : System.Windows.Forms.Form

{

private System.Windows.Forms.Button btnResolve;

private System.Windows.Forms.Button btnClear;

private System.Windows.Forms.Button btnAbout;

private System.Windows.Forms.ListBox lbResults;

private System.Windows.Forms.TextBox txtHost;

private System.ComponentModel.Container components = null;

public DnsResolver()

{

InitializeComponent();

}

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.btnResolve = new System.Windows.Forms.Button();

this.txtHost = new System.Windows.Forms.TextBox();

this.lbResults = new System.Windows.Forms.ListBox();

this.btnClear = new System.Windows.Forms.Button();

this.btnAbout = new System.Windows.Forms.Button();

this.SuspendLayout();

//

// btnResolve

//

this.btnResolve.Location = new System.Drawing.Point(24, 64);

this.btnResolve.Name = "btnResolve";

this.btnResolve.TabIndex = 0;

this.btnResolve.Text = "&Resolve";

this.btnResolve.Click += new System.EventHandler(this.btnResolve_Click);

//

// txtHost

//

this.txtHost.Location = new System.Drawing.Point(8, 24);

this.txtHost.Name = "txtHost";

this.txtHost.Size = new System.Drawing.Size(160, 21);

this.txtHost.TabIndex = 1;

this.txtHost.Text = "";

//

// lbResults

//

this.lbResults.ItemHeight = 12;

this.lbResults.Location = new System.Drawing.Point(176, 8);

this.lbResults.Name = "lbResults";

this.lbResults.Size = new System.Drawing.Size(296, 232);

this.lbResults.TabIndex = 2;

//

// btnClear

//

this.btnClear.Location = new System.Drawing.Point(24, 112);

this.btnClear.Name = "btnClear";

this.btnClear.TabIndex = 3;

this.btnClear.Text = "&Clear";

this.btnClear.Click += new System.EventHandler(this.btnClear_Click);

//

// btnAbout

//

this.btnAbout.Location = new System.Drawing.Point(24, 160);

this.btnAbout.Name = "btnAbout";

this.btnAbout.TabIndex = 4;

this.btnAbout.Text = "&About...";

this.btnAbout.Click += new System.EventHandler(this.btnAbout_Click);

//

// DnsResolver

//

this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);

this.ClientSize = new System.Drawing.Size(504, 253);

this.Controls.AddRange(new System.Windows.Forms.Control[] {

this.btnAbout,

this.btnClear,

this.lbResults,

this.txtHost,

this.btnResolve});

this.Name = "DnsResolver";

this.Text = "Dns Resolver";

this.ResumeLayout(false);

}

#endregion

///

/// 应用程序的主入口点。

///

[STAThread]

static void Main()

{

Application.Run(new DnsResolver());

}

void DnsResolved(IAsyncResult ar)

{

IPHostEntry entry=Dns.EndResolve(ar);

foreach(IPAddress ip in entry.AddressList)

{

lbResults.Items.Add("address: "+ip.ToString());

}

foreach(string alias in entry.Aliases)

{

lbResults.Items.Add("alias: "+alias.ToString());

}

lbResults.Items.Add("resolve done.");

}

private void btnResolve_Click(object sender, System.EventArgs e)

{

if( txtHost.Text=="" ) return;

lbResults.Items.Add("resolve beginning...");

IAsyncResult ar=Dns.BeginResolve(txtHost.Text,new AsyncCallback(DnsResolved),null);

if (!ar.AsyncWaitHandle.WaitOne(2000,false))

{

lbResults.Items.Add("two seconds elapsed, failed");

}

}

private void btnClear_Click(object sender, System.EventArgs e)

{

lbResults.Items.Clear();

}

private void btnAbout_Click(object sender, System.EventArgs e)

{

string str="a tool to get the addresses & aliases of a host\n"

+"by xuhx\n"

+"email:xuhx20@hotmail.com/xuhx2012@sina.com";

MessageBox.Show(str,this.Text,MessageBoxButtons.OK,MessageBoxIcon.Information);

}

}

}