If you are developing a Windows Phone 7 application as part of a team, you will need to be able to allow others on your team to deploy that application to their phones so they can test it before it is released to the marketplace. Before releasing the application to the Windows Phone Marketplace, you may also decide to allow users to download and use the application for free for a trial period. After development and testing of your application is complete, and a trial period is put in place, you make your application available to others via the Windows Phone Marketplace.
When you build your application, the files needed to run it are packaged in a single file deployed to the target device, which can be the Emulator or a Windows Phone device. The files are packaged in what is called a .xap file.
The .xap file is really nothing more than a .zip file with the extension set to .xap instead of .zip. In fact, if you want to view the contents of the .xap file, all you need to do is change the extension to .zip and open the file. If you open the .xap file from the "Try It" section in Lesson 22, you will find six files.
There are three image files, two .xml files, and one .dll file. The ApplicationIcon.jpg file is displayed to the left of your application name within the list of applications on the Windows Phone. The Background.png file is the image used as the background for the pages within your application. ...