Dr. Dobb's Journal - September 2008 - (Page 46)

d09thom_p3ds 7/14/08 12:52 PM Page 46 State of the Art THE ANDROID MOBILE PHONE PLATFORM Android has the potential to change the way we work with mobile phones Can Sexy be Easy? YES - and now Sexy can be FREE! Check out our NEW release: Servoy 4.0 is an Eclipse Plug-In with a FREE community edition! Download today at www.servoy.com/sexy What is Servoy? Here's an excerpt from a recent eWeek product review: “For those tired of maintaining separate code bases for Web and desktop applications, Servoy offers a way to consolidate those code bases and cut development time in half.” To write Android applications, you extend an Activity and add code that implements your design (as in Java ME). You soon appreciate onCreate(), where you can place initialization code with error recovery. This is also where you create an instance of a View that manages your application’s window with its UI. However, you can’t do much with a View until you understand how to use Android’s XML layout file to create the visual objects and interactive widgets that are children of the View. This layout file contains custom XML tagged elements that represent widgets—buttons, text-entry boxes, and labels. Because placement of widgets and the flow of events among them is hierarchical, by nesting the order of the XML tags, you arrange the screen layout and the position of its widgets. The XML is saved into a file in the res/layout/ directory. When you build the Android application, it compiles the layout file’s XML elements into resources that you reference by ID number. To create its UI, the Activity first assigns its visual content to a View that uses your XML file. Then it makes an instance of the View, using ID numbers to obtain the appropriate widget resources that comprise the layout. Android’s use of XML to organize the UI layout lets you—within limits—tinker with the interface without modifying code in the View. It would be nice to have a visual editor that gave you a better idea of how changes to the XML nesting affects the UI’s layout. I made a simple layout that filled the screen and presented a background image. Using Blender3D, I took the 3D model of the Dr. Dobb’s rocket that I used for a previous article (www.ddj.com/mobile/193104855) and rendered it into a 2D PNG bitmap image. Processing key presses with Android’s key event handlers felt similar to those in a MIDlet, where only the method names and some arguments had changed. It didn’t take long to have a rocket scooting around the screen. The program, SpaceActivity, is available online (see “Resource Center,” page 5). One Android shift that tripped me up was getting the screen’s size—values that are often crucial when designing a program’s gameplay. In a MIDlet’s constructor, you 46 Dr. Dobb’s Journal l www.ddj.com l September 2008 http://www.ddj.com/mobile/193104855 http://www.servoy.com/sexy http://www.servoy.com/sexy http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - September 2008

Dr. Dobb's Journal - September 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Developer’s Notebook A Conversation With Erik Demaine Application Lifecycle Management Meets Model-Driven Development Building a Robust Development Environment Real Users Really Matter Matching Wildcards: An Algorithm The Android Mobile Phone Platform Managing Application Thread Use Signalling Integer Overflows in Java .NET Development & the IBM WebSphere Portal Server The Agile Edge Effective Concurrency Swaine’s Flames

Dr. Dobb's Journal - September 2008

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