Consuming Web Services and the Handheld Device

.Net Web Service enables consumers to create rich applications that can access Web Service data--such as GPS--from a Pocket PC. To learn more read on.

Consuming Web Services

.NET Web Services is a form of distributed computing that enables your application to use the logic of a remote component over the Internet using standard protocols. Web Services is one of the most exciting aspects of using the Compact Framework on a mobile device such as Pocket PC, because it enables you to create rich applications that can access Web Service data from one or many sources without being tethered to a desktop.

For example, consider a Pocket PC device that has a GPS unit attached to it over the serial port (you may someday even be able to use a Pocket PC Phone Edition device to request your current position based on the nearest cellular tower). You could hypothetically use a Web Service to request a map of you current surroundings based on the longitude and latitude that the GPS provides. You could then access another Web Service to get a list of the ATMs or restaurants in your local area. By using Web Services, your applications can focus on tying remote data together into a useful program, rather than concentrate on how to get the data to your device, or replicate functionality that has already been developed elsewhere.

The .NET Compact Framework supports the following functionality regarding Web Services on a Pocket PC device:

  • n All Web Services must be based on the HTTP protocol. Other protocols, such as SMTP, are not supported.
  • n Data is transmitted using the Simple Object Access Protocol (SOAP) XML format.
  • n The Compact Framework supports consuming Web Services by client applications only, and does not natively support hosting them. If you need to support hosting a Web Service using the Compact Framework, you can manually build an HTTP listener (using the TcpListener class) and manually handle incoming SOAP requests.

TIP: A great Web site for finding Web Services that are publicly available on the Internet is www.xmethods.com. There you can find Web Services for everything from currency conversion to stock quotes.

In the next section, you will learn what is involved on the client side to consume a Web Service on the Pocket PC.

The Microsoft TerraServer Web Service

The Microsoft TerraServer, located at http://terraserver.microsoft.com, is a massive database (about 3.3 terabytes) of both satellite images and topographic maps for much of the United States. By using TerraServer's search engine, you can zoom in on aerial images for almost any street in the U.S., as well as obtain data about surrounding landmarks. Terra¬Server fortunately also provides a Web Service that you can use to perform queries and get maps from the database (which is rather nice, as it would be rather difficult to store all 3.3 terabytes on a Pocket PC).

In this section, we will use the TerraServer Web Services (also called TerraService) as an example of how you can use and consume .NET Web Services on a Pocket PC device using the .NET Compact Framework. More information about the Web Service API that TerraServer provides is available at http://terraserver.homeadvisor.msn.com/webservices.aspx.

The first thing you need to do to consume a Web Service is create a new project. To do this, select the Smart Device Application project type under the Visual C# Project tree. For this example, let's call the new proj¬ect TerraServiceTest.

After the project has been created, you need to add a new reference for the Web Service you are planning to use in your class. All you need to do is right-click on References in the Solution Explorer and select Add Web Reference (see Figure 12.1).

The Add Web Reference dialog box will appear (see Figure 12.2). In it, you specify the URL for the WSDL or ASMX file that describes the Web Service. The TerraServer Web Service description is located at http://terraserver.homeadvisor.msn.com/TerraService.asmx.

After you have entered the URL, click the Add Reference button. This will cause Visual Studio to generate a proxy class that will be used by your project to access the Web Service. Once this has completed, you will notice that the reference to the Web Service is now in your project (see Figure 12.3).

Now, all you need to do to use the TerraServer Web Service is add the namespace to your current project as follows:

 using TerraServiceTest.com.msn.homeadvisor.terraserver; 

That's it! Your C# program can now use the APIs and structures that are part of the Web Service just as if the component were on the device.

Let's take a look at some sample code that uses TerraService to download a "tile" of satellite image data for the Redmond, Washington, area:

using System; using System.Data; using System.IO; using TerraServiceTest.com.msn.homeadvisor.terraserver; namespace TerraServiceTest { ///

Summary description for Class1. class Class1 { /// The main entry point for the /// application. static void Main(string[] args) { // Create a new TerraService object TerraService ts = new TerraService(); // Build a place to request tile information on Place pl = new Place(); pl.City = "Redmond"; pl.State = "WA"; pl.Country = "USA"; PlaceFacts pf = ts.GetPlaceFacts(pl); // Get the bounding box for the area AreaBoundingBox abb = ts.GetAreaFromPt(pf.Center, Theme.Photo, Scale.Scale16m, 640, 480); // Grab the center tile Byte[] imageBytes = ts.GetTile(abb.Center. TileMeta.Id); // Create a new file and dump the buffer to it FileStream outputFileStream = new FileStream ("map.jpg", FileMode.CreateNew); BinaryWriter outputBinaryWriter = new BinaryWriter (outputFileStream); // Write outputBinaryWriter.Write(imageBytes, 0, imageBytes. Length); // Clean up outputBinaryWriter.Close(); outputFileStream.Close(); } } }

After the class has completed, you can view the downloaded map by launching Pocket Internet Explorer (see Figure 12.4).

Use the following table of contents to navigate to chapter excerpts, or click here to view Chapter 12 in its entirety.



.NET Compact Framework
  Home: Introduction
 Part 1: .NET Compact Framework
 Part 2: Networking with the Compact Framework
 Part 3: Winsock, .NET and the Compact Framework
 Part 4: Internet Protocols and the .NET Pluggable Protocol Mode
 Part 5: Consuming Web Services and the Handheld Device
 Part 6: Pocket PC and P/Invoke
ABOUT THE BOOK:   
Pocket PC Network Programming is a comprehensive tutorial and reference for writing network applications on Pocket PC 2002 and Pocket PC 2002 Phone Edition devices. It explains how the Pocket PC communicates with the Internet, with other mobile devices, and with networks. Click here to purchase the book from Addison-Wesley.
ABOUT THE AUTHOR:   
Steve Makofsky is a software design engineer on Microsoft's .NET XML Messaging team. In addition to having been a Microsoft Embedded MVP, he has worked on several commercial Windows CE products, including the award-winning bUSEFUL Utilities 1.0 and 2.0 (Best of Comdex Utility 1998/1999). Steve coauthored Teach Yourself Windows CE Programming in 24 Hours (Sams, 1999) and has published several magazine articles on .NET and mobile device development. When not working on cool embedded projects, Steve likes to drink lattes and hike on Mt. Everest.
This was first published in December 2006
This Content Component encountered an error

Pro+

Features

Enjoy the benefits of Pro+ membership, learn more and join.

0 comments

Oldest 

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

-ADS BY GOOGLE

MicroscopeUK

SearchCloudProvider

SearchSecurity

SearchStorage

SearchNetworking

SearchCloudComputing

SearchConsumerization

SearchDataManagement

SearchBusinessAnalytics

Close