Dr. Dobb's Journal - September 2008 - (Page 45)

d09thom_p3ds 7/14/08 9:34 AM Page 45 and enters the paused state. At this point, the other Activity’s UI window can come to the foreground and interact with users. What happens to the Activity next depends on several things. If the foreground application only partially obscures the screen, the Activity hovers in the paused state, as users might bring it back to the foreground at any moment. If the foreground application’s window completely covers the screen, onStop() is called and the Activity enters the stopped state. This state is similar to the paused state, except that for lowmemory situations, Android might dispose of its window. If the Activity returns to the foreground later, calls to onRestart() and onStart() restore the window and UI. In very low memory situations, Android might kill the Activity to release memory. If users select the Activity again, it must be completely restarted and its context restored from saved Bundles. As Figure 3 illustrates, the additional methods and states let the Activity cleanly resume execution whether it’s been paused, stopped, or destroyed. Listing One (a) Java ME class DrawScreen extends Canvas implements CommandListener { private int width; private int height; DrawScreen() { // Constructor width = getWidth(); height = get Height(); } (b) Android class SpaceView extends View { public SpaceView(Context context, AttributeSet attrs, Map inflateParams) { super(context, attrs, inflateParams); } // constructor // This method called at startup or when screen changes. // w, h,-- current screen's width and height // oldw, oldh -- previous screen's width and height @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); mX = w; // Get screen's width mY = h; // Get screen's height } // onSizeChanged Test Ride The Android SDK is a free 80-MB download (code.google.com/android/documentation .html). The preferred developer toolset is Eclipse 3.3 (Europa), which also requires the JDT plug-in, Java Development Kit (JDK) 5 or 6, and optionally the Web Services Tool (WST). I installed the software on a Dell Latitude with a 2.4-GHz Mobile Pentium 4 CPU equipped with 512 MB of RAM. The SDK documentation has a step-by-step procedure for installing the necessary software and getting the requisite “Hello World!” sample Android application up and running. The integration between the Eclipse IDE and the Dalvik emulator that implements the Android environment and executes your Android application code is very good. Because I’m always dealing with software rocket science, an application that moved a rocket around the screen seemed an ideal project to explore Android’s features and quirks. Google’s example Android code was a trove of information. I borrowed some code from its Lunar Lander game and other examples to get started. September 2008 l www.ddj.com l Dr. Dobb’s Journal 45 http://code.google.com/android/documentation.html http://code.google.com/android/documentation.html 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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