[WCF-Discovery]让服务自动发送上/下线通知[实例篇]
在《原理篇》我们对客户端如何监听通知，以及服务在上下线时如何发送通知从原理上进行了深入地剖析。我们现在通过一个简单的实例演示如何通过ServiceDiscoveryBehavior服务行为为寄宿的服务添加一个实现上/下线通知的AnnouncementEndpoint终结点，以及客户端如何通过对AnnouncementService服务的寄宿实现对通知的监听和接收。[源代码从这里下载]
我们采用如右图所示的解决方案结构，其中Service.Interface、Service（控制台程序）和Client（控制台程序），用于用于定义服务契约、服务类型（服务寄宿）和客户端监听程序。并且直接使用我们熟悉的CalculatorService。现在我们为该服务的寄宿定义如下一段配置。我们定义了一个包含ServiceDiscoveryBehavior行为的默认服务行为，并且一个UdpAnnouncementEndpoint终结点被添加到了ServiceDiscoveryBehavior的AnnouncementEndpoints集合之中。
1: <configuration>
2: <system.serviceModel>
3: <services>
4: <service name="Artech.WcfServices.Service.CalculatorService">
5: <endpoint address="http://127.0.0.1:3721/calculatorservice"
6: binding="ws2007HttpBinding"
7: contract="Artech.WcfServices.Service.Interface.ICalculator" />
8: </service>
9: </services>
10: <behaviors>
11: <serviceBehaviors>
12: <behavior>
13: <serviceDiscovery>
14: <announcementEndpoints>
15: <endpoint kind="udpAnnouncementEndpoint" />
16: </announcementEndpoints>
17: </serviceDiscovery>
18: </behavior>
19: </serviceBehaviors>
20: </behaviors>
21: </system.serviceModel>
22: </configuration>然后通过如下一段简短的代码对CalculatorService进行寄宿，与之前的不同之处在于输出了一段程序退出的提示性文字。当服务寄宿程序启动后输入任何字符，服务将会被关闭（离线）。
1: using System;
2: using System.ServiceModel;
3: namespace Artech.WcfServices.Service
4: {
5: class Program
6: {
7: static void Main(string[] args)
8: {
9: using (ServiceHost host = new ServiceHost(typeof(CalculatorService)))
10: {
11: host.Open();
12: Console.WriteLine("Enter any key to exit.");
13: Console.Read();
14: }
15: }
16: }
17: }接下来我们需要在客户端通过寄宿AnnouncementService服务来监听CalculatorService服务启动和关闭自动发出的通知。我们先通过如下所示的一段配置为寄宿的AnnouncementService添加一个UdpAnnouncementEndpoint终结点。
1: <configuration>
2: <system.serviceModel>
3: <services>
4: <service name="System.ServiceModel.Discovery.AnnouncementService">
5: <endpoint kind="udpAnnouncementEndpoint" />
6: </service>
7: </services>
8: </system.serviceModel>
9: </configuration>AnnouncementService服务通过如下的代码进行寄宿。由于AnnouncementService被定义成一个单例服务，我们就可以直接针对一个预先创建好的AnnouncementService实例来创建用于服务寄宿的ServiceHost。在服务开启之前，我们注册了AnnouncementService的OnlineAnnouncementReceived和OfflineAnnouncementReceived两个事件，在它接收到目标服务上/下线通知的时候会输出目标服务终结点的地址和契约名称。
1: using System;
2: using System.ServiceModel;
3: using System.ServiceModel.Discovery;
4: namespace Artech.WcfServices.Client
5: {
6: class Program
7: {
8: static void Main(string[] args)
9: {
10: AnnouncementService announcementService = new AnnouncementService();
11: announcementService.OnlineAnnouncementReceived += (sender, e) =>
12: {
13: string contractTypes = string.Empty;
14: Console.WriteLine("Receive Service Online Announcement.");
15: Console.WriteLine("\tAddress: {0}", e.EndpointDiscoveryMetadata.Address.Uri);
16: Console.WriteLine("\tContract: {0}", e.EndpointDiscoveryMetadata.ContractTypeNames[0]);
17: };
18: announcementService.OfflineAnnouncementReceived += (sender, e) =>
19: {
20: string contractTypes = string.Empty;
21: Console.WriteLine("Receive Service Offline Announcement.");
22: Console.WriteLine("\tAddress: {0}", e.EndpointDiscoveryMetadata.Address.Uri);
23: Console.WriteLine("\tContract: {0}", e.EndpointDiscoveryMetadata.ContractTypeNames[0]);
24: };
25: using (ServiceHost host = new ServiceHost(announcementService))
26: {
27: host.Open();
28: Console.Read();
29: }
30: }
31: }
32: }客户端和服务端所有的配置和编码工作完成之后，先启动客户端开启通知监听服务。然后开启服务端启动服务CalculatorService，最后输入任意键（不要直接关闭控制台窗口）退出服务端程序。此时你会发现客户端的控制台上具有如下的输出。这段文字的第一部分代表CalculatorService启动的时候（ServiceHost的Open方法被执行之后）发出的上线通知，后一部分代表服务关闭（ServiceHost的Dispose方法执行之后）发出的离线通知。
1: Receive Service Online Announcement.
2: Address: http://127.0.0.1:3721/calculatorservice
3: Contract: http://www.artech.com/:ICalculator
4: Receive Service Offline Announcement.
5: Address: http://127.0.0.1:3721/calculatorservice
6: Contract: http://www.artech.com/:ICalculator