Android App Development Guide

Hoisington, Android Bootcamp for Developers Using Java, 4th Edition. © 2024 Cengage. All Rights Reserved. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole or in part. 1
1
Android Bootcamp
for Developers
Using Java, 4e
Chapter 1: Voilà! Meet the
Android
duplicated, or posted to a publicly accessible website, in whole or in part.

Icebreaker
• The class will be broken up into pairs of students.
• Each student will create three questions to ask their partner:
− One true/false question
− One question that can be answered with a number
− One question that requires a short answer
• Partners will take turns asking the questions they’ve prepared.
• Each student will then introduce their partner to the class using the information
they’ve learned.

Chapter Objectives (1 of 2)
When you complete this chapter, you will be able to:
• 01.01 Describe the market for Android applications
• 01.02 Identify the role of the Android platform in the mobile market
• 01.03 Describe the features of the Android phone
• 01.04 Identify the languages used in Android development
• 01.05 Describe the role of Google Play in the marketplace

• 01.06 Understand the connection between Windows and Android
• 01.07 Create an Android project using Android Studio
• 01.08 Design the user interface layout within the virtual device
• 01.09 Execute an Android application on an emulator
• 01.10 Open a saved Android project in Android Studio

1.1 Understanding the Market for Android
Applications
• Two primary mobile operating systems
− iOS for iPhone
− Google Android
• Recently, the Google Android phone has become the sales leader
• Apps: mobile applications created for smartphones

1.2 The Role of the Android in the Mobile
Market
• Open-Source Platform
− Android is an open-source operating system—no company or individual defines
the features or direction of the development
− Open Handset Alliance: an open-source business alliance of 80 firms that develop
standards for mobile devices
• Android Open-Source Devices
− Android smartphones, tablets, and smartwatches are sold by many companies
− As you develop an app, you test it using an emulator, which duplicates how the
app looks and feels on a particular device

1.3 Features of the Android Phone (1 of 3)
Feature Description
3D graphics The interface can support 3D graphics for a 3D interactive game experience or 3D
image rendering.
Split screen A split-screen, multiwindow feature displays more than one Android application at
the same time. Watch a movie on the left side and hold a video call with your
friends who are also watching the movie.
Dark mode The Dark mode feature helps to save the phone’s battery life. Blank white space
consumes more power and drains the battery.
Facial recognition Android provides this high-level feature for automatically identifying or verifying a
person’s face from a digital image or a video frame.
Front- and rear-facing
camera
Android phones can use either a front- or rear-facing camera, allowing developers
to create applications involving video calling.

Feature Description
Multiple language
voice-to-text support
Android supports multiple human languages. Android provides a feature of
converting text to speech in different languages. Text messages can be read aloud
to help people who are visually impaired.
On-screen keyboard The on-screen keyboard offers suggestions for spelling corrections as well as
options for completing words you start typing. The on-screen keyboard also
supports voice input.
Power management Android identifies programs running in the background that are using memory and
processor resources. You can close those apps to free up the phone’s processor
memory, extending the battery power.
Gaming For optimized gaming, Android supports the use of a gyroscope, gravity and
barometric sensors, linear acceleration, and rotation vectors, which provide game
developers with highly sensitive and responsive controls.

Feature Description
Voice-based
recognition
Android recognizes voice actions for calling, texting, and navigating with the phone.
Wi-Fi Internet tethering Android supports tethering, which allows a phone to be used as a wireless or wired
hotspot that other devices can use to connect to the Internet.

1.4 Languages Used in Android Development
(1 of 4)
• Java is an object-oriented programming language patterned after the C++
language
• Java and Kotlin can be used to code Android apps
• Android Studio
− An integrated development environment (IDE) for building and integrating
application development tools and open-source projects
− Includes the Android Software Development Kit (SDK)
− XML is used to assist in the layout of the Android emulator

(2 of 4)
Figure 1-4 Android Studio
running Java code

(3 of 4)
• Android Emulator
− Design, develop, prototype, and test Android apps without using a physical
device
− Mimics almost every feature of a real Android handset, except placing phone
calls
• Versions of Android
− First release was 1.0 (September 2008)
− Each subsequent release adds features and fixes known bugs

(4 of 4)
• Versions of Android (continued)
− Android has adopted a naming system based on treats/desserts
− When the revision level reached 10.0, Android started emphasizing revision
number over names
− Most recent versions were Android 12.0 (Snow Cone, October 2021) and
Android 13.0 (Tiramisu, October 2022)

Activity 1.1: Knowledge Check
(1 of 2)
1. What is the name of the organization that sets the standards for Android
mobile devices?
2. Name at least four types of devices that run the Android OS.

(2 of 2)
3. Should a developer target only the most recent version of the Android OS
when creating an app?
4. What is the name of the current version of the Android OS?

Activity 1.1: Knowledge Check Answers
(1 of 2)
1. What is the name of the organization that sets the standards for Android
mobile devices?
Answer: Open Handset Alliance
2. Name at least four types of devices that run the Android OS.
Answer: Smartphones, foldable phones, tablets, watches, MP4 players,
automobiles, and Internet TVs

(2 of 2)
3. Should a developer target only the most recent version of the Android OS
when creating an app?
Answer: No. To support as many Android devices as possible, you should set
the minimum development version to the lowest available that allows your app
to provide its core feature set.
4. What is the name of the current version of the Android OS?
Answer: Android 13.0 (internal name: Tiramisu)

1.5 Google Play in the Marketplace (1 of 2)
• The Android platform consists of the Android OS, application development tools,
and a marketplace
• Apps are compiled into package files with an .apk extension
• Google Play (http://play.google.com) sells and deploys all apps
• Programs must meet minimum standards, including:
− Reliability
− Efficiency
− Performance

1.5 Google Play in the Marketplace (2 of 2)
• Developers must sign an agreement and pay a one-time registration fee
(currently $25) to publish apps on Google Play
• Apps offered for free are free to publish
• For paid apps, standard split is 85% of sales for the developer and 15% for
wireless carriers for the first $1 million of annual earnings selling digital goods or
services
• Also sold through the Amazon Appstore
− Pays developers 80% of the sale price for sold apps and grants 10% of their
Appstore revenue as an Amazon Web Services credit

1.6 The Connection between Windows and
Android
• Beginning with Windows 11, you can download Android apps to your PC from
the Microsoft Store
• Android apps are also available for Windows-based tablets and other touch
devices
• Phone Link App
− The Microsoft Phone Link app allows you to connect an Android phone to a
Windows 11 PC
− Enables text messaging, notifications, and transfer of photos from the phone
on the PC

1.7 Creating an Android Project Using
Android Studio (1 of 8)
• Install Android Studio from developer.android.com/studio
• Opening Android Studio to Create a New Project
− Name: the human-readable title for your app
− Package name: the Java package namespace for the source code
− Save location on your hard drive or USB drive
− Minimum SDK: the minimum API level required by your app
− Language (Java or Kotlin)

• Creating the Hello Android World Project
− Android Studio facilitations app creation for various form factors
− Two most common projects: Empty Activity and Basic Project
− To create a new Android project, you open Studio, click the New Project
button, and make selections and entries for the project specs

Figure 1-8 Welcome to
Android Studio window

Figure 1-9 New Project
window with Empty Activity

Figure 1-10 Creating Empty
Activity

Figure 1-11 Android Studio
project view

• Building the User Interface
− The user interface must be intuitive
− The user interface must not distract from functionality
− Java code or XML layout files are needed
− The XML method is preferred because it allows you to design a user
interface without writing large amounts of code

• The Android Project View
− The Android project view contains the key source application folders for a
project: manifests, java, and res
− The manifests folder includes the AndroidManifest.xml file, which
contains all the information about the application that Android needs to run
− The java folder contains the Java code source files
− The res folder contains resources the app may need: images, music, video,
and the user interface named activity_main.xml

1.8 The User Interface Layout within the
Virtual Device (1 of 12)
• The Android SDK includes layout files called activity_main.xml in the res/layout
folder of the app
• The Layout Editor contains the Palette, Component Tree, toolbar, Design
editor, and Attributes pane
• Layout: a container that holds as many widgets as needed
• Widget: a single element (a.k.a. object), such as a Button from the Palette

Figure 1-12 Coding window in
Android Studio

• The Attributes pane contains the attributes and settings of the currently active
app project or object
• Attribute: a characteristic of an object that describes what that object can do
• Android Studio displays an emulator configuration called the Android Virtual
Device (AVD) for design and layout purposes
• To change the virtual device, you open the activity_main.xml file to open the
Layout Editor, then click the Device for Preview (D) button and select the
desired device

Figure 1-13 Layout Editor for
emulator layout design

Figure 1-14 Device for
Preview button

Figure 1-15 Generic phone
selected for Device for
Preview

• When you select the default TextView component, its text is displayed in the
Component Tree
− The Component Tree displays widgets in the order they were placed on the
emulator
• Within the Common Attributes section of the Attributes pane, you can see the
text attribute of the component, which is the text it contains

Figure 1-16 Design editor

Figure 1-17 Attributes pane

• The TextView Component
− Text can be updated by:
 Changing the hard-coded value for the text attribute in the Attributes
pane
 Modifying resource files
 Changing the application XML source code
− It is good programming practice to add an id attribute to each component
(object) for use in Java code

Figure 1-18 Emulator with
TextView control and text
attribute

Figure 1-19 The id attribute

1.9 Executing an Android Application on an
Emulator (1 of 2)
• The Android emulator (virtual device) runs slowly
− Even when idling, it consumes significant CPU time
• To run and automatically save your app, click the Run button
• Click the Terminate button to stop the emulator from running

1.9 Executing an Android Application on an
Emulator (2 of 2)
Figure 1-20 Hello Android
World app displayed in
emulator

1. In Android Studio, objects such as buttons and text boxes are called _____.
2. Java code source files are stored in the _____ folder.
3. Testing the app is done in a(n) _____.

1. In Android Studio, objects such as buttons and text boxes are called _____.
Answer: widgets
2. Java code source files are stored in the _____ folder.
Answer: java
3. Testing the app is done in a(n) _____.
Answer: emulator

1.10 Opening a Saved Android Project in
Android Studio
• To load a saved project, open Studio and then choose the project to open
− Click on it in the Recent Projects column or
− Click Open an existing Android Project in the Quick Start column, navigate to
it, and click the OK button

Self-Assessment
1. After reading about the market and requirements for software development for
Android devices, what skills would you like to gain or improve before you
begin developing Android apps for publication? What aspects of the market for
these apps would you like to learn more about?
2. What is your initial impression of the Android Studio and Android SDK tools
available to you as an Android developer?

Summary
• Click the link to review the objectives for this presentation.
Chapter objectives

48
Android Bootcamp
for Developers
Using Java, 4e
Chapter 2: Simplify! The Android
User Interface

• 02.01 Develop a user interface using the TextView, ImageView, and Button
components
• 02.02 Add text using the String table in the Translations Editor
• 02.03 Construct the user interface using a ConstraintLayout
• 02.04 Plan out program design
• 02.05 Create multiple Android activities

• 02.06 View activities in the Android Manifest file
• 02.07 Write code using the onCreate( ) method
• 02.08 Create a Button event handler
• 02.09 Code a Button event handler
• 02.10 Correct errors in code
• 02.11 Run the completed app in the emulator

2.1 Designing an Android App (1 of 5)
Figure 2-1 Easy Recipes
Android app (left)
Figure 2-2 Second screen with
recipe (right)

• Designing apps is like constructing a building
• The Big Picture: To create the Easy Recipes app, you follow a set of steps that
you repeat every time you create an Android application
− Create the user interface (XML layout) for every screen
− Create a Java class (Activity) for every screen
− Code each Java class with appropriate objects and actions
− Test the application in the Android phone emulator

• Using the Android User Interface
− Interface: the space where interactions occur between people and the app
− Android apps run on various form factors
− The layout is stored as XML code
 Special Android-formatted XML code is extremely compact
 XML is a set of instructions for placing components on the screen

Figure 2-4 Creating an empty
activity for the Easy Recipes
app

Figure 2-5 Android
Studio open and
ready for you to
design the Easy
Recipes app

2.2 Using the String Table in the Translations
Editor (1 of 5)
• The Translations Editor in Android Studio can display the original text in the
language in which it was programmed, or the language of the current locale plus
culturally specific settings
• The String Table
− Android provides the strings.xml file or String table inside the Resources
folder
− strings.xml: a default file that is part of every Android application and
contains commonly used strings for an application
− string: a series of alphanumeric characters that can include spaces

Editor (2 of 5)
• The String Table (continued)
− Localization: the use of the String table to change text based on the user’s
preferred language
− Every string is composed of a key (a.k.a. id attribute), which is the name of
a component, and a default value, which is the text associated with the
component
− To create an application that is accessible to those with visual disabilities,
add descriptions to the user interface components that can be read out
loud to your user by a speech-based accessibility service such as a screen
reader

Editor (3 of 5)
Figure 2-7 The strings.xml tab
displaying XML code

Editor (4 of 5)
Figure 2-10 Adding another
string to the String table

Editor (5 of 5)
Figure 2-11 Completed String
table on the Translations
Editor tab

2.3 Constructing the User Interface with the
ConstraintLayout (1 of 18)
• The Android user interface includes a layout resource designer called the
ConstraintLayout in the Component Tree
− Organizes how components appear on the app’s screens
− Provides more flexibility in positioning components than other layouts
− Constraints: the building blocks in an Android layout that attach or align a
component to the screen, either by attaching it vertically and horizontally to
the edges of the screen or aligning it with another component (or parent) on
the screen
− Constraints are used to create a Responsive Design UI

• Constraint Handles
− Four circular dots on the edges of a selected component
− A Constraint component must have at least two constraints—a vertical and a
horizontal one
− If you drag all four Constraint handles to the four edges of the emulator
screen, you can then drag the component anywhere on the screen and it will
stay in that location when you run the app
− In the ConstraintLayout, a nonconstrained component will float to the top of
the screen when the app is run

• Constraint Handles (continued)
− A white Constraint handle means
that the component is not aligned
− A blue Constraint handle means
that the component is aligned with
the screen or another component
− Corner boxes resize the
component
Figure 2-12 The four circles
are Constraint handles

• XML Code
− After you move the Constraint handles in the Design view, Android Studio
updates your layout resources as XML code in the res/layout resource
directory
− Other common layouts used in Android Studio include:
 LinearLayout
 RelativeLayout
 TableLayout
 GridView

Figure 2-13 ConstraintLayout
XML code

• The Easy Recipes Opening User Interface: To change a component's attributes,
select it and use the Attributes pane
• Android Text Attributes
− The text attribute uses text from a string resource to display within the
component
− The textSize attribute can use various units of measurement
 The preferred unit is often sp (scaled-independent pixels)
 Other units: inches (in), millimeters (mm), pixels (px), density-
independent pixels (dp or dip)

Figure 2-16 The text attribute
with @string used to display
the String table

Figure 2-17 TextView text
displayed in emulator after
@string selected

Figure 2-18 Updating the
textSize of the TextView
component

• Adding a File to the Resources Folder
− Graphics used in ImageView components must first be placed in the
res/drawable folder
− Android supports .png (preferred), .jpg (acceptable), and .gif (discouraged)
graphic formats
− Android categorizes device screens based on size and density
− Android creates a Drawable resource for images when you save them in the
res/drawable folder

Figure 2-19 The sorbet.png
file copied into the drawable
folder within the res folder

• The ImageView Component
− An ImageView component can display an icon, a company logo, or a
graphic on the Android screen
− Reminder: The image to be used should be placed in a drawable resources
folder before the ImageView component is placed in the emulator

Figure 2-23 ImageView
component with image
displayed in the emulator and
the id entered

Figure 2-24 The
contentDescription set for
accessibility

• Adding a Button Component
− Button components are commonly used in GUIs
− The Android SDK includes four types of button components: Button,
FloatingActionButton, ToggleButton, and ImageButton
− backgrountTint: an attribute that can be added to a component to set a
background color
− textColor: an attribute that sets the color of the text in a component

Figure 2-26 Button
component placed on
emulator and the id named

Figure 2-27 Button displaying
larger text

Figure 2-28 Button with
colors displayed for
background tint color

Activity 2.1: Knowledge Check (1 of 2)
1. List the major steps you follow to create an Android application.
2. Android loads text resources from the project's _____.
3. Which Android layout provides flexibility in positioning components and
facilitates making your layout a Responsive Design UI?

4. Which unit of measurement is often preferred for the textSize attribute? Why?
5. To display an illustration or photo in an Android app you use a(n) _____.

(1 of 2)
1. List the major steps you follow to create an Android application.
Answer: (1) Create the user interface (XML layout) for each screen.
(2) Create a Java class (Activity) for every screen.
(3) Code each Java class with the appropriate objects and actions.
(4) Test the application in the emulator.
2. Android loads text resources from the project's _____.
Answer: string table or strings.xml file
3. Which Android layout provides flexibility in positioning components and
facilitates making your layout a Responsive Design UI?
Answer: ConstraintLayout

(2 of 2)
4. Which unit of measurement is often preferred for the textSize attribute? Why?
Answer: sp (scaled-independent pixels), because it will scale the font to meet
the user's size preference
5. To display an illustration or photo in an Android app you use a(n) _____.
Answer: ImageView component

2.4 Planning Out Program Design
• Phases in the program development life cycle:
− Gather and analyze the program requirements
− Design the user interface
− Design the program processing objects
− Code the program
− Test the program
• Creating Activities
− Activity: a screen, constructed from XML files and a Java class

2.5 Creating Multiple Android Activities
(1 of 2)
• A class describes a group of objects and serves as a blueprint, or template, for
creating those objects
• An object is a specific, concrete instance of a class
• When you create an object, you instantiate it, meaning you define one
particular variation of the object within a class
• Each screen represents one Activity, and each Activity must have a matching
Java class file within the java folder
• The convention is to use Pascal case for Java class names

2.5 Creating Multiple Android Activities
(2 of 2)
Figure 2-34 New Recipe class
in the Easy Recipes project

2.6 Viewing Activities in the Android Manifest
File (1 of 3)
• The Android Manifest file (AndroidManifest.xml) contains:
− The name of the Java application
− A listing of each activity
− Permissions needed to access other Android functions (such as the Internet,
services, and broadcast receivers)
− The minimum level of the Android API
• Android Studio automatically adds each activity you create to the Android
Manifest file

File (2 of 3)
Figure 2-35
AndroidManifest.xml

File (3 of 3)
• Coding the Android Activity
− The entry point of the Activity class is the onCreate() event handler method
 Where you initialize the Activity by placing it on the top of Android's stack
of Activities
− Method: a set of Java statements that can be included inside a Java class; a
piece of code that performs some type of action
− Method body: a collection of statements that defines what the method does

2.7 Writing Code Using the onCreate()
Method (1 of 2)
• Syntax for the onCreate() method:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
• This method has a void return type, which means it does not return anything
• The Java code necessary to display the content of a specific screen is called
SetContentView, which has the following syntax:
setContentView(R.layout.activity_main);

2.7 Writing Code Using the onCreate()
Method (2 of 2)
Figure 2-36 MainActivity.java
code for onCreate( ) method

2.8 Creating a Button Event Handler
(1 of 3)
• Event handler: a part of a program coded to respond to a specific event
• Tapping a button is called a click event in Java code
• Java code for an event handler must contain the following sections:
− A class attribute to hold a reference to the Button object:
Button = (Button)findViewById(R.id.btRecipe);
 Includes the findViewById() method to find a layout XML file
− An OnClickListener() method to await the button click action's onClick()
method to respond to the click event

(2 of 3)
• When you import the Button type as an Android widget, the button package
becomes available throughout the app
− An import statement makes more Java functions available to your app
• After the Button attribute is referenced in MainActivity.java, an OnClickListener()
method is necessary to detect when the user taps an on-screen button
• When an OnClickListener is placed in the code window, Java creates an onClick
auto-generated stub—a piece of code that serves as a placeholder to declare
itself

(3 of 3)
• Syntax for an OnClickListener() method that listens for a Button:
button.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
• The startActivity() method creates an intent to start another Activity
− Two parameters: context and name of Activity to open
− Syntax: startActivity(new Intent(MainActivity.this,
Recipe.class));

2.9 Coding a Button Event Handler
(1 of 3)
Figure 2-38 Button
instantiated with Button
library added

(2 of 3)
Figure 2-40 The
setOnClickListener added
with auto-complete feature

(3 of 3)
Figure 2-41 Complete code
for MainActivity.java—
startActivity will launch the
second screen’s Recipe.class
when the user clicks the
button

1. Name the phases of the development life cycle in order.
2. The file included in each Android application that provides essential
information such as the minimum API level to the Android device is called
_____.

3. Which Java method initializes an Android Activity?
4. A part of a program that responds to a user interaction such as tapping an on-
screen button is called a(n) _____.
5. Which Java method is necessary to detect a user interaction with the app?

(1 of 2)
1. Name the phases of the development life cycle in order.
Answer:
(1) Gather and analyze the program requirements.
(2) Design the user interface.
(3) Design the program processing objects.
(4) Code the program.
(5) Test the program.
2. The file included in each Android application that provides essential
information such as the minimum API level to the Android device is called
_____.
Answer: the Android Manifest or AndroidManifest.xml

(2 of 2)
3. Which Java method initializes an Android Activity?
Answer: onCreate()
4. A part of a program that responds to a user interaction such as tapping an on-
screen button is called a(n) _____.
Answer: event handler
5. Which Java method is necessary to detect a user interaction with the app?
Answer: OnClickListener()

2.10 Correcting Errors in Code
Figure 2-42 Syntax error

2.11 Saving and Running the Application
• Each time an Android application is tested in the emulator, the programming
design and code are automatically saved
• Click the toolbar's Save All button to save the project
• Click the toolbar’s Run app button to test the application in the emulator
− The first time an app is executed, you will be prompted to choose an
emulator

Self-Assessment
1. What is your opinion of the Android Studio user interface design tools? Are
there any improvements you'd like to see? Which tools do you anticipate using
most often when creating or updating Android apps?
2. When creating the app project for Chapter 2, which did you enjoy more:
working with the XML layout tools in Studio or writing Java code? How do you
expect to use these UI creation skills in your future career?

Summary
Chapter objectives

105
Android Bootcamp
for Developers
Using Java, 4e
Chapter 3: Engage! Android
User Input, Variables, and
Operations

• 03.01 Collect user input
• 03.02 Add a Text Number component
• 03.03 Add a string array
• 03.04 Change the background attribute
• 03.05 Set the hint attribute for a Text component
• 03.06 Develop a user interface using a Spinner component

• 3.07 Add a prompt and entries to a Spinner component
• 3.08 Code the EditText class for the Text Number component
• 3.09 Code the Spinner component
• 3.10 Instantiate the Button component and variables
• 3.11 Code the getText() method

• 3.12 Understand arithmetic operations
• 3.13 Code the setText( ) method

3.1 Collecting User Input (1 of 4)
Figure 3-1 Opening screen for
Concert Tickets app

• Processes required to create this application:
− Define display text using the Translations Editor and strings.xml file
− Set the background color
− Define a Text Number component
− Define a Spinner component
− Convert string data to numeric data
− Perform arithmetic operations with user-entered data
− Display the results, properly formatted, to the user

• Simplifying User Input
− The onscreen keyboard is called a soft keyboard
− Input can come in the form of tapping or gestures (using two fingers to pan,
rotate, or zoom)
− The primary design challenge is to simplify the user experience
 Use legible fonts, simplify input, and optimize each device’s capabilities
to maximize user experience

• Using Android Text Components
− Text entered via a soft or physical keyboard is the most common type of
mobile input
− Text components can request different input types (e.g., plain text, phone
number, various types of numeric values)
− The component type can constrain the characters available
• User Experience
− User experience refers to all aspects of interaction with a device

3.2 Adding a Text Number Component
(1 of 3)
• You can use the id attribute in the Attributes pane to enter a name that begins
with the prefix tv (for TextView)
− Use descriptive names like tvTickets
• Using the String Table
− String items displayed in the components of an app can be stored in the
string table (strings.xml)
− A string array can be used to store a group of related strings

(2 of 3)
Figure 3-5 Adding strings in
the Translations Editor

(3 of 3)
Figure 3-6 String table

3.3 Adding a String Array (1 of 2)
• A string array defines a string resource of related items in a central location
within strings.xml
• An item defines an individual entry within a string array
• As you type the string array XML code, the Android Studio editor offers
suggestions in a panel that can complete a statement

3.3 Adding a String Array (2 of 2)
Figure 3-9 The string array
named tvGroup with three
items added in XML code

3.4 Changing Background Attributes
(1 of 4)
• The Android background feature can help provide an app's individual flair
• The background is white by default
• To change it, set the background attribute in the Attributes pane

(2 of 4)
Figure 3-10 Changing the
background color

(3 of 4)
Figure 3-11 Title added to
emulator

(4 of 4)
Figure 3-12 Adding a Text
Number component

3.5 Setting the Hint Attribute for a Text
Component (1 of 2)
• A hint is a short description of a component that is visible as gray text (also
called a watermark) inside a Text Number component or any Text input
− Often used to provide guidelines about the input expected in a component
for the user
• You can change the color of the hint by changing the textColorHint attribute
− May be necessary to ensure adequate contrast between the text and
background

3.5 Setting the Hint Attribute for a Text
Component (2 of 2)
Figure 3-15 Warning symbol
removed from Text Number
component

1. If a component holds multiple text strings, it is best to store them in a(n)
_____.
2. To change the screen color for an activity in your app, you set the _____.
3. When you see gray text describing what sort of data to enter within a text entry
box in an app, you are looking at a(n) _____.

1. If a component holds multiple text strings, it is best to store them in a(n)
_____.
Answer: string array
2. To change the screen color for an activity in your app, you set the _____.
Answer: background attribute
3. When you see gray text describing what sort of data to enter within a text entry
box in an app, you are looking at a(n) _____.
Answer: hint

3.6 Developing a User Interface Using a
Spinner Component
• A Spinner component is similar to a
drop-down list for selecting a single
item from a fixed list
• The Spinner component displays a
prompt with a list of strings called
items
• Figure 3-16 Spinner dialog box
displaying the three concert groups

3.7 Adding a Prompt and Entries to a Spinner
Component (1 of 6)
• A prompt, which can be used to display instructions at the top of the Spinner
control, is stored in strings.xml and is named prompt
• Using Entries
− The Spinner attribute called entries connects the string array in strings.xml
to the Spinner component so the entries can be displayed in the application
− The spinnerMode attribute sets the component to dialog mode or drop-
down mode
− The layout_width and layout_height attributes set the dimensions

Component (2 of 6)
Figure 3-18 Pick a Resource
dialog box with tvGroup
string array selected

Component (3 of 6)
• Adding the Button, TextView, and ImageView Controls
− ImageView components should have a content description for visually
impaired users
− This description is provided by setting the contentDescription attribute

Component (4 of 6)
Figure 3-20 Adding a Button
component

Component (5 of 6)
Figure 3-21 Adding a
TextView component

Component (6 of 6)
Figure 3-22 Adding an
ImageView component with a
contentDescription attribute

3.8 Coding the EditText Class for the Text
Number Component (1 of 2)
• A Java variable is used to contain data that changes during the execution of a
program
• A final variable can be initialized only once
− Attempting to reassign the value results in a compile error when the
application runs
• For the concert tickets app, you insert code to create the tickets variable
containing the extracted EditText class text:
final EditText tickets =
(EditText)findViewById(R.id.tvTickets);

3.8 Coding the EditText Class for the Text
Number Component (2 of 2)
Figure 3-23 EditText code for
Text Number component

3.9 Coding the Spinner Control
Figure 3-24 Spinner
component code

3.10 Instantiating the Button Component and
Variables (1 of 6)
• An OnClickListener waits in the background and listens for the user to click a
button
• Clicking the button activates a Button event, triggering the Button event OnClick
handler to execute the associated code
• Code to instantiate the TextView component to a variable named result is used
to display the result of the ticket price calculation in the concert tickets app:
final TextView result =
((TextView)findViewById(R.id.tvResult));

Variables (2 of 6)
Figure 3-27 TextView
component code for the
result

Variables (3 of 6)
• Declaring Variables
− Two steps are necessary in order to use a variable: (1) declare the variable
and (2) assign a value to the variable
− The declared type of a variable determines which operations are allowed
− Java has eight built-in primitive (simple) types of data
• Primitive Data Types
− Java requires all variables to have a data type

Variables (4 of 6)
Type Meaning Range Default Value
byte Often used with arrays –128 to 127 0
short Often used with arrays –32,768 to 32,767 0
int Most commonly used number value –2,147,483,648 to 2,147,483,647 0
long Used for numbers that exceed int –9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
0
float A 32-bit floating-point number +/–3.40282347 ^38 0
double Most common for decimal values +/–1.79769313486231570 ^308 0
char Used for single characters Characters 0
boolean Used for conditional statements True or false False

Variables (5 of 6)
• Primitive Data Types (continued)
− Sample variable initialization and declarations:
double costPerTicket = 89.99;
int numberOfTickets;
double totalCost;
String groupChoice;
• The String Data Type
− The String type is a class and not a primitive data type
− A string can be a character, word, or phrase

Variables (6 of 6)
• The String Data Type (continued)
− Most strings used in Java are objects of type String (e.g.,
String groupChoice;)
• Declaring the Variables in the Project
− Typically declared at the beginning of an activity
− Variables must be declared before you can use them

3.11 Coding the getText() Method
(1 of 2)
• Data stored in the EditText component can be read with the getText() method
• Data is read in as a string, by default
• A Parse class is used to convert strings into numbers
− Parse types include Integer.parseInt(), Float.parseFloat(),
Double.parseDouble(), and Long.parseLong()
• Sample code to extract a string and convert it into an integer:
numberOfTickets =
Integer.parseInt(tickets.getText().toString());

3.11 Coding the getText() Method
(2 of 2)
• Working with Mathematical Operations
− The ability to perform arithmetic operations is fundamental to many
applications
− Most programs require arithmetic operations to add, subtract, multiply, and
divide numeric data

1. A drop-down list for an Android app is created using a(n) _____.
2. The attribute that connects the choices for a drop-down list to their component
is called _____.
3. Which Java keyword prevents a variable from being reassigned?
4. Which Java method reads text stored in an EditText component?

1. A drop-down list for an Android app is created using a(n) _____.
Answer: Spinner component
2. The attribute that connects the choices for a drop-down list to their component
is called _____.
Answer: entries
3. Which Java keyword prevents a variable from being reassigned?
Answer: final
4. Which Java method reads text stored in an EditText component?
Answer: getText()

3.12 Understanding Arithmetic Operators
(1 of 3)
• Java's arithmetic operators are + (addition), – (subtraction), * (multiplication), /
(division), % (remainder), ++ (increment 1), and -- (decrement 1)
• The order of operations determines the sequence for performing calculations
when multiple operators are included in an expression
− Parentheses; ++ & --; *, /, & %; + & – (left to right)
• Formatting Numbers
− Java includes a class called DecimalFormat that provides patterns for
formatting numbers for output on the Android device

(2 of 3)
Figure 3-30 Calculating and
formatting the ticket cost

(3 of 3)
• Displaying Android Output: Computed results must be displayed
• Using the getSelectedItem() Method
− The getSelectedItem() method returns the text label of the currently
selected Spinner item
− Sample code that assigns a selected item to a String variable named
groupChoice:
groupChoice = group.getSelectedItem( ).toString( );

3.13 Coding the setText() Method
• The setText() method displays text in a TextView component
• You can concatenate text and string variable values using +, e.g.,
String mobile = "Android";
String completeSentence = mobile + " is a platform.";
• Sample statement using the setText() method to display text in a TextView
component named result:
result.setText("Cost for " + groupChoice + " is " +
currency.format(totalCost));

Self-Assessment
1. At this point, how comfortable are you using Java classes such as String and
Parse to accomplish the goals of a program? What else would you like to learn
about these Java classes?
2. Consider the Java methods used to code the sample concert ticket
application. How do you anticipate using these methods for your own app
development? What would their most common use cases be for you?

Summary
Chapter objectives

152
Android Bootcamp
for Developers
Using Java, 4e
Chapter 4: Explore! Icons and
Decision-Making Components

• 04.01 Create an Android project with a custom icon
• 04.02 Display the Action bar icon using code
• 04.03 Place a RadioGroup and RadioButtons in Android applications
• 04.04 Determine layouts with the layout:margin attributes
• 04.05 Align components using the foregroundGravity attributes

• 04.06 Add a RadioButton Group
• 04.07 Write code for a RadioButton component
• 04.08 Make decisions with conditional statements
• 04.09 Make decisions using an If statement
• 04.10 Make decisions using an If Else statement

• 04.11 Make decisions using logical operators
• 04.12 Display an Android toast notification
• 04.13 Use the isChecked() method with RadioButtons
• 04.14 Make decisions using nested If statements

4.1 Creating an Android Project with a
Custom Icon (1 of 12)
• We will be creating an app to convert pounds to kilograms and kilograms to
pounds
• App is designed to be used in a hospital setting to administer medication to
patients based on patient weight
• Hospital scales register pounds, whereas medication dosages are based on
patient weight in kilograms
• Formulas needed:
− Kilograms = pounds * 2.2
− Pounds = kilograms / 2.2

Figure 4-1 Opening screen of
the Medical Calculator
Figure 4-2 Results screen of
the Medical Calculator

• Steps to complete the app:
− Create a customized launcher icon
− Use code to add the icon for display in the Action bar
− Define a TextField for the data entry of the weight of the patient
− Define a RadioGroup to select a conversion of pounds to kilograms or
kilograms to pounds
− Display a toast message for data validation
− Convert data so it can be used for arithmetic operations

• Steps to complete the app (continued):
− Perform arithmetic operations on data the user enters
− Display formatted results

• Using the Launcher Icon
− The launcher icon opens the app from the home screen and represents the
app when it is published to Google Play
− A high-quality launcher icon can influence users to purchase your app
− Icons can establish brand identity
− Simple images with clear visual cues have a memorable impact
− Vector-based graphics are best for icon design because these images can
be easily scaled without loss of detail

• Using the Launcher Icon (continued)
− Google Play specifies the size and format of all launcher icons
− Should be saved with the .png file format/extension
− When you publish an app to Google Play, you must provide a 512 × 512-
pixel, high-resolution application icon in the developer console as you upload
your program
 This icon is displayed on the Google Play site to provide a description of
the app and does not replace your launcher icon
− Google Play's naming convention for launcher icons: ic_launcher

Resolution Dots Per Inch (dpi) Size (px)
ldpi (low-density screen) 120 36 × 36
mdpi (medium-density screen) 160 48 × 48
hdpi (high-density screen) 240 72 × 72
xhdpi (extra high-density screen) 320 96 × 96
xxhdpi (extra extra high-density screen) 480 144 × 144
xxxhdpi (extra extra extra high-density screen) 640 192 × 192

• Customizing a Launcher Icon
− Image Asset Studio: Android Studio tool that helps you generate your own
app icons from images
 Generates a set of icons at the appropriate resolution for each pixel
density your app supports
− Use the built-in Image Asset Studio wizard to create these multiple icons and
store them in the correct folders

Figure 4-6 Default launcher
icons in the Asset Studio

Figure 4-7 Custom launcher
icons

Figure 4-8 Confirmed icon
path in Asset Studio displayed
in res/mipmap folders

Figure 4-9 Resized custom
icons and their pathways in
the mipmap folder

4.2 Displaying the Action Bar Icon Using
Code (1 of 4)
• An Action bar icon is considered a logo that represents what the program’s
function is in a single glance
− For example, the medical symbol conveys the purpose and identity of the
app
• Supporting code needed in MainActivity.java to display the image in the Action
bar:
getSupportActionBar().setDisplayShowHomeEnabled(true);
getSupportActionBar().setLogo(R.mipmap.ic_launcher);
getSupportActionBar().setDisplayUseLogoEnabled(true);

Code (2 of 4)
Figure 4-11 Icon displayed in
running app in the emulator

Code (3 of 4)
• String Table
− String resources are stored within the /res/values/strings.xml file
− Any strings you add to the strings.xml file are accessible within your
application

Code (4 of 4)
Figure 4-12 Translations
Editor with new strings in the
String table

4.3 Placing a RadioGroup and RadioButtons
in Android Applications (1 of 2)
• RadioButton components are used to select or deselect an option
− Can be arranged horizontally or vertically
− Have a label defined by the Text attribute
− Checked attribute can be set to true or false
− Typically used together in a RadioGroup container
 Only one RadioButton in the group can be selected at a time
− It saves time to offer a default selection (checked = true) for the option that is
used most often
172

4.3 Placing a RadioGroup and RadioButtons
in Android Applications (2 of 2)
• Changing the Text Color of RadioButton and CheckBox Components
− Hexadecimal color code: a triplet of three colors
 Example: #FF0000 is a true red
 Color system used by the Android platform
− Codes range from 00 to FF (00 = none, FF = full)
− Codes are identified by a pound sign, followed by the red, green, and blue
values contained in the color
173

4.4 Determining Layouts with the
layout:margin Attributes
• You can change a component's alignment after placing it on the UI by adjusting
its Gravity settings
• The layout:margin attribute allows for more flexibility in controlling your layout
− You can change all margins equally or change the left, top, right, and bottom
margins individually
• Set density-independent pixel (dp) values instead of “eyeballing” to create equal
spaces around components
• Using the same specified margins creates a symmetrical layout

(1 of 2)
1. What is an app's opening icon called?
2. What tool can you use to generate a launcher icon from an image?
3. RadioButton components are typically used together in a(n) _____.
4. What is #FF0000?

(2 of 2)
5. What settings are used to change the alignment of an object?
6. Which attribute can you use to set the spacing around each side of an object
individually?

(1 of 2)
1. What is an app's opening icon called?
Answer: The launcher icon
2. What tool can you use to generate a launcher icon from an image?
Answer: Image Asset Studio
3. RadioButton components are typically used together in a(n) _____.
Answer: RadioGroup
4. What is #FF0000?
Answer: The hexadecimal color code for a true red color

(2 of 2)
5. What settings are used to change the alignment of an object?
Answer: Gravity settings
6. Which attribute can you use to set the spacing around each side of an object
individually?
Answer: layout:margin attribute

4.5 Aligning Components Using the
foregroundGravity Attributes
• A component's gravity can be changed using the Attributes pane or with a
toolbar shortcut
• The foregroundGravity tool changes the linear alignment of a component
• Layout gravity is similar to the alignment feature in Microsoft Office that allows a
component to snap to the left, center, right, top, or bottom

4.6 Adding the RadioButton Group and Other
Components (1 of 5)
• When naming a RadioButton with the id attribute, use a name that begins with
the prefix rb, which represents a radio button in the code
• Completing the User Interface
− Remember to create a clean layout and use the entire screen effectively

4.6 Adding the RadioButton Group and Other
Components (2 of 5)
Figure 4-15 Text Number
component and
foregroundGravity attribute
to center hint text

Android App Development Guide

Recommended

Recommended

More Related Content

Similar to Android App Development Guide

Similar to Android App Development Guide (20)

More from MattMarino13

More from MattMarino13 (20)

Recently uploaded

Recently uploaded (20)

Android App Development Guide

Editor's Notes