Managed Code Access to a Web Service

The task of an embedded device is of to "run forever" without intervention performing a specific task as an outcrop of a service. For example it may have sensors that periodically return climatic data or return activity data when events occur in its realm. To demonstrate that functionality the GetTime application will be modified to request the formatted DateTime string from a remote service. In particular a Web Service  will be used to service the DateTime request from the Compact 2013 client.  Whilst it is the Compact 2013 system that is data consumer, it would not be hard for the web method to modified so that it consumed data submitted to it by the Compact 2013 device.

Issues:

• Web referencing not supported in Visual Designer
• The web reference URL can't use localhost.

(A) Create the Web Service

Create a web service to generate the Date/Time string as an XML string. The web service will be written in C# and may reside on the development system or elsewhere except the target Compact 2013 system. The simplest option is to implement it on a system that has IIS implemented, which could even be Azure!. If no IIS web server is available, use the Visual Studio (Virtual) Web Server but you will need something like Fiddler to do port redirection because the Visual Studio server can only be used in the local context. Note that any emulator or virtual machine does not run in the local context of its host.

1. Create the web service in a new solution in a separate instance of Visual Studio if using the OS/App development system, or on a separate system:
   Create a new project
   Menu, File—>New—> Project—>C#
   Set the .NET version to 3.5 
   —>ASP.NET Web Service
2. Call it GetTimeSvc and generate the project
3. If using the Visual Studio Web Server, in the Property Pages, set the IP Port to a fixed a port
   • Then Configure Filddler2 for Port Redirection (Reverse Proxy)
4. In Solution Explorer, rename the Service1.asmx page to TimeService.asmx
5. Rename the Service1 class to TimeService
   Right-click on Service1 in the code –>Refactor—>Rename
   Change the name and accept the change.
6. In Solution Explorer, set that page as the Start Page for the web service.
7. Note that the functions exposed as web methods have the [WebMethod] declaration proceeding them.
   In the generated code is a HelloWorld method.
8. Test run the Web Service:
   Right-click on the project in Solution explorer—>Set as Startup Project
   F5 to run it.
9. When the "Debugging Not Enabled" dialog appears, enable debugging for the site.
10. Select the HelloWorld method
11. On the next page invoke it:
    
    
    HelloWorld Web Method Output

    1. xml version="1.0" encoding="utf-8" ?>
    2. <string xmlns="http://tempuri.org/">Hello Worldstring>
    
    Listing 17. The output of HelloWorld web method
    
12. Add the following web method:
    
    
    GetTime Web Method

    2. public string GetTime()
    3. {
    4.     DateTime localTime = DateTime.Now;
    5.     string dateTimeStr = string.Format(
    6.         "Time {0}:{1}:{2} Date {3:2}//{4:2}//{5:4}",
    7.         localTime.Hour, localTime.Minute, localTime.Second,
    8.         localTime.Day, localTime.Month, localTime.Year);
    9.  
    10.     return dateTimeStr;
    11. }
    
    Listing 17. The GetTime web method
    
    Note that for simplicity a StringBuilder is not passed to the web method. For simplicity, the web method returns a string rather than a using pass by reference functionality.
    
13. Test run the web service again and exercise the GetTime web method:
    
    
    GetTime Web Method Output

    1. xml version="1.0" encoding="utf-8" ?>
    2. <string xmlns="http://tempuri.org/">Time  23:52:22 Date  2//2//4string>
    
    Listing 17. The output of GetTime web method
    
14. The absolute URL for the web service is required, Restart the web service and copy the URL in the web browser.
15. Replace localhost in the url with the web server machine name or its IP Address.
16. If using the Visual Studio Server replace the port with the redirected port.
    eg http://192.168.2.105:8000/TimeService/TimeWebService.asmx
17. Test the new URL in the browser.
18. Finally test the URL on another system:
    It is important that the URL for the web service work on a "non-local" system as the target system is "not local" to the web service.
    Non-local in this context can mean on the same subnet but not localhost.

(B) Web Reference

Normally a web reference is added to a .NET app in the project context in Solution Explorer. Once added to a project, the web service is instantiated as an object instance of the web service class, with the required web method being a method of that object.

Unfortunately the addition of web methods in the Visual Designer this has not been implemented for .NET CF 3.9.

It has though been implemented with Compact 7-Smart Device projects. The solution is to generate the app project with the web reference in that context and either copy the binary to the Compact 2013 system or copy the required web reference code and resources from the Compact 7 app project to the Compact 2013 project. The first method is simplest but debugging would need to resolved on the Compact 7 system. The second method is much more complex and can be considered "a hack". But once implemented it facilitates debugging and extensions in the Compact 2013 app development context.

NEXT: Merging the Web References from a VS2008 SmartDevice project into a Compact 2013 C# Project

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