Android Programming: The Big Nerd Ranch Guide, 4th Edition

App Basics

Your GeoQuiz application will consist of an activity and a layout:

• An activity is an instance of Activity, a class in the Android SDK. An activity is responsible for managing user interaction with a screen of information.

  You write subclasses of Activity to implement the functionality that your app requires. A simple application may need only one subclass; a complex application can have many.

  GeoQuiz is a simple app and will start off with a single Activity subclass named MainActivity. MainActivity will manage the user interface, or UI, shown in Figure 1.1.

• A layout defines a set of UI objects and the objects’ positions on the screen. A layout is made up of definitions written in XML. Each definition is used ...