Chapter 4. Under the Covers: Startup Code and Resources in the MJAndroid Application

Chapter 3 introduced the major application we use in this book to illustrate basic Android concepts. That chapter explained which files make up the source code, but it didn't actually cover any source code in the application. We'll start looking at source code in this chapter. And to allow you to get started developing an application quickly, we'll begin with the first task every standalone application has to perform: initialization.

The events covered in this chapter occur between your selecting "Run As Android Application" from the Eclipse menu and seeing the map that MJAndroid displays at startup. This chapter shows how Android makes it easy to create relatively complex applications. In just 80 lines of code and some associated XML resource files, MJAndroid manages to:

• Display an interactive map

• Track the current location of the Android phone and update the map

• Create a local database of information and load user preferences into it

• Provide a dynamically changing menu

• Display user interface elements such as labels, buttons, and spinners

• Run a new Activity to display a supporting screen

The Java code in an Android application interacts tightly with XML resource files, so we'll bounce back and forth between them in this chapter. As we point out repeatedly, XML files are easier to tweak during development and maintain over the life of an application. The design of Android encourages you to specify the look and behavior of the application in the resource files.