App Inventor 2, 2nd Edition

360 Pages·2014·26.81 MB·English

by  David Wolber

Learn to build apps in the fastest way possible
Mobile Development Up
d
Verate
“This is a book for app inventors of all ages. My students loved extending its examples App sion 2d for
into their own creative apps. A great introduction to mobile computing!”
—Ralph Morelli, Trinity College Professor A
p
App Inventor 2
p

I Inventor 2
Yes, you can create your own apps for Android devices—and it’s easy to do. This n
extraordinary book introduces you to App Inventor 2, a powerful visual tool that v
lets anyone build apps. Learn App Inventor basics hands-on with step-by-step e
instructions for building more than a dozen fun projects, including a text answering n
machine app, a quiz app, and an app for finding your parked car!
t
o
The second half of the book features an Inventor’s Manual to help you understand
r
the fundamentals of app building and computer science. App Inventor 2 makes an

excellent textbook for beginners and experienced developers alike. 2
n Use programming blocks to build apps—like working on a puzzle
Create Your Own
n Create custom multimedia quizzes and study guides
W
n Design games and other apps with 2D graphics and animation o
lb Android Apps
n Make a custom tour of your city, school, or workplace e
r
,
n Control a LEGO® MINDSTORMS® NXT robot with your phone A
b
n Build location-aware apps by working with your phone’s sensors e
l
s
n Explore apps that incorporate information from the Web o
n
,
S David Wolber, Hal Abelson,
p
e
David Wolber, a University of San Francisco Professor, teamed up to produce this book with App Inventor
r Ellen Spertus & Liz Looney
creators Hal Abelson, professor of Electrical Engineering and Computer Science at MIT; Ellen Spertus, tu
Associate Professor of Computer Science at Mills College and Senior Research Scientist at Google; and s

&
Liz Looney, Senior Software Engineer at Google and member of the Robotics Task Force.

L
o
o
n
e
y
Twitter: @oreillymedia
facebook.com/oreilly
US $39.99 CAN $41.99
oreilly.com
ISBN: 978-1-491-90684-2
www.it-ebooks.info
Learn to build apps in the fastest way possible
Mobile Development Up
d
Verate
“This is a book for app inventors of all ages. My students loved extending its examples App sion 2d for
into their own creative apps. A great introduction to mobile computing!”
—Ralph Morelli, Trinity College Professor A
p
App Inventor 2
p

I Inventor 2
Yes, you can create your own apps for Android devices—and it’s easy to do. This n
extraordinary book introduces you to App Inventor 2, a powerful visual tool that v
lets anyone build apps. Learn App Inventor basics hands-on with step-by-step e
instructions for building more than a dozen fun projects, including a text answering n
machine app, a quiz app, and an app for finding your parked car!
t
o
The second half of the book features an Inventor’s Manual to help you understand
r
the fundamentals of app building and computer science. App Inventor 2 makes an

excellent textbook for beginners and experienced developers alike. 2
n Use programming blocks to build apps—like working on a puzzle
Create Your Own
n Create custom multimedia quizzes and study guides
W
n Design games and other apps with 2D graphics and animation o
lb Android Apps
n Make a custom tour of your city, school, or workplace e
r
,
n Control a LEGO® MINDSTORMS® NXT robot with your phone A
b
n Build location-aware apps by working with your phone’s sensors e
l
s
n Explore apps that incorporate information from the Web o
n
,
S David Wolber, Hal Abelson,
p
e
David Wolber, a University of San Francisco Professor, teamed up to produce this book with App Inventor
r Ellen Spertus & Liz Looney
creators Hal Abelson, professor of Electrical Engineering and Computer Science at MIT; Ellen Spertus, tu
Associate Professor of Computer Science at Mills College and Senior Research Scientist at Google; and s

&
Liz Looney, Senior Software Engineer at Google and member of the Robotics Task Force.

L
o
o
n
e
y
Twitter: @oreillymedia
facebook.com/oreilly
US $39.99 CAN $41.99
oreilly.com
ISBN: 978-1-491-90684-2
www.it-ebooks.info
App Inventor 2
Create Your Own Android Apps
David Wolber, Hal Abelson,
Ellen Spertus, and Liz Looney
www.it-ebooks.info
App Inventor 2
by David Wolber, Hal Abelson, Ellen Spertus, and Liz Looney
Copyright © 2015 David Wolber, Hal Abelson, Ellen Spertus, and Liz Looney. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions
are also available for most titles (http://safaribooksonline.com). For more information, contact our cor-
porate/institutional sales department: 800-998-9938 or [e-mail].
Editor: Rachel Roumeliotis Indexer: Wendy Catalano
Production Editor: Kara Ebrahim Interior Designer: Monica Kamsvaag
Copyeditor: Dianne Russell Cover Designer: Ellie Volckhausen
Proofreader: Eliahu Sussman Illustrator: Rebecca Demarest
April 2011: First Edition
October 2014: Second Edition
Revision History for the Second Edition
2014-10-03: First Release
See http://oreilly.com/catalog/errata.csp?isbn=9781491906842 for release details.
The O’Reilly logo is a registered trademark of O’Reilly Media, Inc. App Inventor 2 and related trade dress
are trademarks of O’Reilly Media, Inc.
While the publisher and the authors have used good faith efforts to ensure that the information and
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ity for errors or omissions, including without limitation responsibility for damages resulting from the
use of or reliance on this work. Use of the information and instructions contained in this work is at
your own risk. If any code samples or other technology this work contains or describes is subject to
open source licenses or the intellectual property rights of others, it is your responsibility to ensure that
your use thereof complies with such licenses and/or rights.
978-1-491-90684-2
[LSI]
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Table of Contents
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Part I. AI2 Tutorials
1. HelloPurr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
What You’ll Learn 1
The App Inventor Environment 2
Designing the Components 3
Live Testing 8
Adding Behaviors to the Components 10
Downloading the App to Your Android Device 16
Sharing the App 17
Variations 17
Summary 18
2. PaintPot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
What You’ll Learn 20
Getting Started 20
Designing the Components 20
Adding Behaviors to the Components 25
The Complete App: PaintPot 35
Variations 36
Summary 36
3. MoleMash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
What You’ll Build 37
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iv Contents
What You’ll Learn 37
Getting Started 38
Designing the Components 38
Adding Behaviors to the Components 42
The Complete App: MoleMash 48
Variations 49
Summary 49
4. No Texting While Driving. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
What You’ll Learn 52
Getting Started 52
Designing the Components 53
Adding Behaviors to the Components 54
The Complete App: No Texting While Driving 64
Variations 65
Summary 66
5. Ladybug Chase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
What You’ll Build 67
What You’ll Learn 67
Designing the Components 68
Adding Behaviors to the Components 71
The Complete App: Ladybug Chase 83
Variations 84
Summary 85
6. Paris Map Tour. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
What You’ll Learn 87
Designing the Components 88
Setting the Properties of ActivityStarter 88
Adding Behaviors to the Components 89
The Complete App: Map Tour with Activity Starter 93
The Complete App: Map Tour (Web Viewer) 96
Variations 96
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Contents v
Summary 97
7. Android, Where’s My Car?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
What You’ll Learn 99
Getting Started 99
Designing the Components 100
Adding Behaviors to the Components 102
The Complete App: Android, Where’s My Car? 111
Variations 112
Summary 112
8. Presidents Quiz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
What You’ll Learn 113
Getting Started 114
Designing the Components 114
Adding Behaviors to the Components 115
The Complete App: The Presidents Quiz 127
Variations 128
Summary 129
9. Xylophone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
What You’ll Build 131
What You’ll Learn 131
Getting Started 132
Designing the Components 132
Creating the Keyboard 133
Recording and Playing Back Notes 138
The Complete App: Xylophone 144
Variations 145
Summary 146
10. MakeQuiz and TakeQuiz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
What You’ll Learn 148
Getting Started 148
Designing the Components 148
Adding Behaviors to the Components 150
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vi Contents
The Complete App: MakeQuiz 158
TakeQuiz: An App for Taking the Quiz in the Database 158
The Complete App: TakeQuiz 161
Variations 162
Summary 163
11. Broadcast Hub. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
What You’ll Learn 166
Getting Started 166
Designing the Components 166
Adding Behaviors to the Components 168
The Complete App: Broadcast Hub 179
Variations 181
Summary 181
12. Robot Remote. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
What You’ll Learn 183
Getting Started 184
Designing the Components 184
Adding Behaviors to the Components 187
Driving the NXT 192
Using the Ultrasonic Sensor to Detect Obstacles 194
Variations 196
Summary 197
13. Amazon at the Bookstore. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
What You’ll Learn 199
What is an API? 200
Getting Started 202
Designing the Components 202
Programming the App’s Behavior 204
The Complete App: Amazon at the Bookstore 210
Customizing the API 211
Variations 211
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Contents vii
Summary 211
Part II. Inventor’s Manual
14. Understanding an App’s Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Components 216
Behavior 216
An App as a Recipe 216
An App as a Set of Event Handlers 217
Event Types 219
Event Handlers Can Ask Questions 221
Event Handlers Can Repeat Blocks 222
Event Handlers Can Remember Things 223
Event Handlers Can Interact with the Web 223
Summary 224
15. Engineering and Debugging an App. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Software Engineering Principles 225
Solve Real Problems 226
Build a Prototype and Show Users 226
Incremental Development 226
Design Before Coding 227
Comment Your Code 228
Divide, Layer, and Conquer 228
Understand Your Language: Tracking with Pen and Paper 229
Debugging an App 232
Watching Variables 233
Testing Individual Blocks 233
Incremental Development with Do It 234
Disabling Blocks 234
Summary 234
16. Programming Your App’s Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Named Memory Slots 235
Properties 235
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viii Contents
Defining Variables 236
Setting and Getting a Variable 237
Setting a Variable to an Expression 238
Incrementing a Variable 238
Building Complex Expressions 239
Displaying Variables 240
Local Variables 240
Summary 241
17. Creating Animated Apps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Adding a Canvas Component to Your App 243
The Canvas Coordinate System 243
Animating Objects with Timer Events 245
Creating Movement 246
Speed 247
Collision Detection 247
EdgeReached 247
CollidingWith and NoLongerCollidingWith 248
Interactive Animation 249
Specifying Sprite Animation Without a Clock Timer 250
Summary 252
18. Programming Your App to Make Decisions: Conditional Blocks. . . . . . . . . . . . . . . . . . . . 253
Testing Conditions with if and else if Blocks 254
Programming an Either/Or Decision 255
Programming Conditions Within Conditions 255
Programming Complex Conditions 256
Summary 260
19. Programming Lists of Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
Creating a List Variable 261
Selecting an Item in a List 262
Using an Index to Traverse a List 262
Example: Traversing a List of Paint Colors 263
Creating Input Forms and Dynamic Data 265
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