Beginning Android™ Application Development

Chapter 3. Getting to Know the Android User Interface

WHAT YOU WILL LEARN IN THIS CHAPTER

• The various ViewGroups you can use to lay out your views

• How to adapt to changes in screen orientation

• How to manage screen orientation changes

• How to create the UI programmatically

• How to listen for UI notifications

In Chapter 2, you learned about the Activity class and its life cycle. You learned that an activity is a means by which users interact with the application. However, an activity by itself does not have a presence on the screen. Instead, it has to draw the screen using Views and ViewGroups. In this chapter, you will learn the details about creating user interfaces in Android, how users interact with them. In addition, you will learn how to handle changes in screen orientation on your Android devices.

UNDERSTANDING THE COMPONENTS OF A SCREEN

In Chapter 2, you saw that the basic unit of an Android application is an activity. An activity displays the user interface of your application, which may contain widgets like buttons, labels, text boxes, and so on. Typically, you define your UI using an XML file (e.g., the main.xml file located in the res/layout folder), which may look like this:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"

android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" ...