System.Net名称空间包含了DNS类，它可以提供了编写DNS所需要的函数。下面讲解DNS类的一些方法以及在C#中如何利用该类编写程序。 一、 同步方法 在DNS类中定义了四个同步方法：GetHostName()、GetHostByName()、GetHostByAddress()、Resolve()。下面分别讲解。 1、public static string GetHostName(); 功能：获取本地计算机的主机名。 返回值：字符串，包含本地计算机的 DNS 主机名。 2、public static IPHostEntry GetHostByName(string hostName) 功能：获取指定 DNS 主机名的 DNS 信息。 参数：包含主机的 DNS 名的字符串 using System; using System.Net; class GetDNSHostInfo { public static void Main(string[] argv) { if (argv.Length != 1) { Console.WriteLine("Usage: GetDNSHostInfo hostname"); return; } IPHostEntry results = Dns.GetHostByName(argv[0]); Console.WriteLine("Host name: {0}",results.HostName); foreach(string alias in results.Aliases) { Console.WriteLine("Alias: {0}", alias); } foreach(IPAddress address in results.AddressList) { Console.WriteLine("Address: {0}", address.ToString()); } } } 注：IPHostEntry（为 Internet 主机地址信息提供容器类）属性介绍： AddressList：获取或设置与主机关联的 IP 地址列表。 Aliases：获取或设置与主机关联的别名列表。 HostName：获取或设置主机的 DNS 名称。 3、GetHostByAddress() 功能：获取 IP 地址的 DNS 主机信息。 public static IPHostEntry GetHostByAddress(IPAddress); public static IPHostEntry GetHostByAddress(string); using System; using System.Net; class GetDNSAddressInfo { public static void Main(string)[] argv) { if (argv.Length != 1) { Console.WriteLine("Usage: GetDNSAddressInfo address"); return; } IPAddress test = IPAddress.Parse(argv[0]); IPHostEntry iphe = Dns.GetHostByAddress(test); Console.WriteLine("Information for {0}", test.ToString()); Console.WriteLine("Host name: {0}", iphe.HostName); foreach(string alias in iphe.Aliases) { Console.WriteLine("Alias: {0}", alias); } foreach(IPAddress address in iphe.AddressList) { Console.WriteLine("Address: {0}", address.ToString()); } } } 注：IPAddress，提供网际协议 (IP) 地址。 4、public static IPHostEntry Resolve(string hostName) 功能：将 DNS 主机名或 IP 地址解析为 IPHostEntry 实例。 参数：DNS 样式的主机名或 IP 地址。 备注：Resolve 方法在 DNS 服务器中查询与主机名或 IP 地址相关联的 IP 地址。当 hostName 是 DNS 样式的主机名并且与多个 IP 地址关联时，仅返回解析为该主机名的第一个 IP 地址。 using System; using System.Net; class GetResolveInfo { public static void Main(string[] argv) { if (argv.Length != 1) { Console.WriteLine("Usage: GetResolveInfo address"); return; } IPHostEntry iphe = Dns.Resolve(argv[0]); Console.WriteLine("Information for {0}", argv[0]); Console.WriteLine("Host name: {0}", iphe.HostName); foreach(string alias in iphe.Aliases) { Console.WriteLine("Alias: {0}", alias); } foreach(IPAddress address in iphe.AddressList) { Console.WriteLine("Address: {0}",address.ToString()); } } } 二、 异步方法 在DNS中定义了四个异步方法: BeginGetHostByName()、BeginResolve()、EndGetHostByName()、EndResolve() 使用范例： using System; using System.Drawing; using System.Net; using System.Text; using System.Windows.Forms; class AsyncResolve Form: { TextBox address; ListBox results; private AsyncCallback OnResolved; public AsyncResolve() { Text = "DNS Address Resolver"; Size = new Size(400,380); OnResolved = new AsyncCallback(Resolved); Label label1 = new Label(); label1.Parent = this; label1.Text = "Enter address to resolve:"; label1.AutoSize = true; label1.Location = new Point(10, 10); address = new TextBox(); address.Parent = this; address.Size = new Size(200, 2 * Font.Height); address.Location = new Point(10, 35); results = new ListBox(); results.Parent = this; results.Location = new Point(10, 65); results.Size = new Size(350, 20 * Font.Height); Button checkit = new Button(); checkit.Parent = this; checkit.Text = "Resolve"; checkit.Location = new Point(235,32); checkit.Size = new Size(7 * Font.Height, 2 * Font.Height); checkit.Click += new EventHandler(ButtonResolveOnClick); } void ButtonResolveOnClick(object obj, EventArgs ea) { results.Items.Clear(); string addr = address.Text; Object state = new Object(); Dns.BeginResolve(addr, OnResolved, state); } private void Resolved(IAsyncResult ar) { string buffer; IPHostEntry iphe = Dns.EndResolve(ar); buffer = "Host name: " + iphe.HostName; results.Items.Add(buffer); foreach(string alias in iphe.Aliases) { buffer = "Alias: " + alias; results.Items.Add(buffer); } foreach(IPAddress addrs in iphe.AddressList) { buffer = "Address: " + addrs.ToString(); results.Items.Add(buffer); } } public static void Main() { Application.Run(new AsyncResolve()); } }
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