Laying Out the UILaying Out the UI
Open app/res/layout/activity_quiz.xml. If you see a graphical preview of the file, select the Text
tab at the bottom to see the backing XML.
Currently, activity_quiz.xml defines the default activity layout. The defaults change frequently, but
the XML will look something like Listing 1.1.
Listing 1.1 Default activity layout (activity_quiz.xml)
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_quiz"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="16dp"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:paddingTop="16dp"
tools:context="com.bignerdranch.android.geoquiz.QuizActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"/>
The default activity layout defines two widgets: a RelativeLayout and a TextView.
Widgets are the building blocks you use to compose a UI. A widget can show text or graphics, interact
with the user, or arrange other widgets on the screen. Buttons, text input controls, and checkboxes are
all types of widgets.
The Android SDK includes many widgets that you can configure to get the appearance and behavior
you want. Every widget is an instance of the View class or one of its subclasses (such as TextView or
Button).