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书名: Beginning Android

作者: Mark Murphy

出版日期: June 22, 2009

页数: 384

ISBN: ISBN-10: 1430224193 ISBN-13: 978-1430224198

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this print for content only—size & color not accurate spine = 0.885" 384 page count
Books for professionals By professionals
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Beginning Android
Dear Reader,
First, welcome to the world of Android! Were entering a new era of mobile
application development, one marked by open platforms and open source, to
take ‘walled gardens’ and make them green houses for any and all to participate
in. Android is relatively easy for developers, and I believe that this innovation
will help generate a large ecosystem of developers and consumers within a
very short time. This means that budding developers such as yourself will have
many opportunities to design and build your own applications and you’ll have
a huge and hungry customer base.
Second, welcome to the book! Its purpose is to start you on your way with
building Android applications, and to help you master the learning curve.
Android is already a rich framework, comparable in many ways to the richness
of desktop Java environments. This means that there is a lot of cool stuff for you
to pick up along your journey in order to create the slickest, most useful apps
you can imagine.
The source code for the code samples in this book is all available from the
Apress site, so you can stay as hands-on and practical as you like while I intro-
duce you to the core of Android, and invite you to experiment with the various
classes and APIs we’ll be looking at. By the time youve finished this book, you’ll
be creating your own Android applications and asking yourself what your next
great application will be...!
Enjoy!
Mark Murphy
US $44.99
Shelve in
Mobile Computing
User level:
Beginner–Intermediate
Murphy
Beginning Android
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in open source
Beginning
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Mark L. Murphy
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Master Android from first principles
and begin the journey toward your
own successful Android applications!
ISBN 978-1-4302-2419-8
9 781430 224198
5 4 4 9 9
Beginning Android
■■■
Mark L. Murphy
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Beginning Android
Copyright © 2009 by Mark L. Murphy
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Contents at a Glance
About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
PART 1 ■ ■ ■ Core Concepts
CHAPTER 1 The Big Picture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
CHAPTER 2 Project Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
CHAPTER 3 Inside the Manifest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
PART 2 ■ ■ ■ Activities
CHAPTER 4 Creating a Skeleton Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
CHAPTER 5 Using XML-Based Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
CHAPTER 6 Employing Basic Widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
CHAPTER 7 Working with Containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
CHAPTER 8 Using Selection Widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
CHAPTER 9 Getting Fancy with Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
CHAPTER 10 Employing Fancy Widgets and Containers . . . . . . . . . . . . . . . . . . . . . 93
CHAPTER 11 Applying Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
CHAPTER 12 Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
CHAPTER 13 Embedding the WebKit Browser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
CHAPTER 14 Showing Pop-Up Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
CHAPTER 15 Dealing with Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
CHAPTER 16 Handling Activity Lifecycle Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
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PART 3 ■ ■ ■ Data Stores, Network Services,
and APIs
CHAPTER 17 Using Preferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
CHAPTER 18 Accessing Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
CHAPTER 19 Working with Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
CHAPTER 20 Managing and Accessing Local Databases . . . . . . . . . . . . . . . . . . . 193
CHAPTER 21 Leveraging Java Libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
CHAPTER 22 Communicating via the Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
PART 4 ■ ■ ■ Intents
CHAPTER 23 Creating Intent Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
CHAPTER 24 Launching Activities and Sub-Activities . . . . . . . . . . . . . . . . . . . . . . 221
CHAPTER 25 Finding Available Actions via Introspection . . . . . . . . . . . . . . . . . . . 231
CHAPTER 26 Handling Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
PART 5 ■ ■ ■ Content Providers and Services
CHAPTER 27 Using a Content Provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
CHAPTER 28 Building a Content Provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
CHAPTER 29 Requesting and Requiring Permissions . . . . . . . . . . . . . . . . . . . . . . 269
CHAPTER 30 Creating a Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
CHAPTER 31 Invoking a Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
CHAPTER 32 Alerting Users via Notifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
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PART 6 ■ ■ ■ Other Android Capabilities
CHAPTER 33 Accessing Location-Based Services . . . . . . . . . . . . . . . . . . . . . . . . . 293
CHAPTER 34 Mapping with MapView and MapActivity . . . . . . . . . . . . . . . . . . . . . 299
CHAPTER 35 Handling Telephone Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
CHAPTER 36 Searching with SearchManager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
CHAPTER 37 Development Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
CHAPTER 38 Where Do We Go from Here? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
APPENDIX Introducing Android 1.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
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Contents
About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
PART 1 ■ ■ ■ Core Concepts
CHAPTER 1 The Big Picture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
What Androids Are Made Of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Content Providers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Intents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Stuff at Your Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Multimedia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
GPS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Phone Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
CHAPTER 2 Project Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Root Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
The Sweat of Your Brow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
The Rest of the Story . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
What You Get Out of It . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
CHAPTER 3 Inside the Manifest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
In the Beginning There Was the Root, and It Was Good . . . . . . . . . . . . . . . 9
Permissions, Instrumentations, and Applications (Oh, My!) . . . . . . . . . . . 10
Your Application Does Something, Right? . . . . . . . . . . . . . . . . . . . . . . . . . 10
Achieving the Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
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viii
CONTENTS
PART 2 ■ ■ ■ Activities
CHAPTER 4 Creating a Skeleton Application . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Begin at the Beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
The Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Dissecting the Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Building and Running the Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
CHAPTER 5 Using XML-Based Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
What Is an XML-Based Layout? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Why Use XML-Based Layouts? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
OK, So What Does It Look Like? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
What’s with the @ Signs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
We Attach These to the Java . . . How? . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
The Rest of the Story . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
CHAPTER 6 Employing Basic Widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Assigning Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Button, Button, Who’s Got the Button? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Fleeting Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Fields of Green. Or Other Colors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Just Another Box to Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Turn the Radio Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
It’s Quite a View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Useful Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Useful Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
CHAPTER 7 Working with Containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Thinking Linearly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Concepts and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Orientation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
LinearLayout Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
All Things Are Relative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Concepts and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
RelativeLayout Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
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Tabula Rasa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Concepts and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
TableLayout Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Scrollwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
CHAPTER 8 Using Selection Widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Adapting to the Circumstances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Using ArrayAdapter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Other Key Adapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Lists of Naughty and Nice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Spin Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Grid Your Lions (or Something Like That . . .) . . . . . . . . . . . . . . . . . . . . . . 62
Fields: Now with 35% Less Typing! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Galleries, Give or Take the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
CHAPTER 9 Getting Fancy with Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Getting to First Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
A Dynamic Presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
A Bit About Inflation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
And Now, Back to Our Story . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Better. Stronger. Faster. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Using convertView . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Using the Holder Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Making a List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
. . . And Checking It Twice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
CHAPTER 10 Employing Fancy Widgets and Containers . . . . . . . . . . . . . . . 93
Pick and Choose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Time Keeps Flowing Like a River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Making Progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Putting It on My Tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
The Pieces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
The Idiosyncrasies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Wiring It Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Adding Them Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Intents and Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Flipping Them Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Other Containers of Note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
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CHAPTER 11 Applying Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Flavors of Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Menus of Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Menus in Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Taking a Peek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Yet More Inflation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Menu XML Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Menu Options and XML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Inflating a Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
CHAPTER 12 Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Love the One You’re With . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
CHAPTER 13 Embedding the WebKit Browser . . . . . . . . . . . . . . . . . . . . . . . . . 129
A Browser, Writ Small . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Loading It Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Navigating the Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
Entertaining the Client . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Settings, Preferences, and Options (Oh, My!) . . . . . . . . . . . . . . . . . . . . . 135
CHAPTER 14 Showing Pop-Up Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Raising Toasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Alert! Alert! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
Checking Them Out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
CHAPTER 15 Dealing with Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Getting Through the Handlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Messages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Runnables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Running in Place . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Where, Oh Where Has My UI Thread Gone? . . . . . . . . . . . . . . . . . . . . . . 145
Now, the Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
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CHAPTER 16 Handling Activity Lifecycle Events . . . . . . . . . . . . . . . . . . . . . . 147
Schroedinger’s Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Life, Death, and Your Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
onCreate() and onDestroy() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
onStart(), onRestart(), and onStop() . . . . . . . . . . . . . . . . . . . . . . . . . 148
onPause() and onResume() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
The Grace of State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
PART 3 ■ ■ ■ Data Stores, Network Services,
and APIs
CHAPTER 17 Using Preferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Getting What You Want . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Stating Your Preference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
And Now, a Word from Our Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Letting Users Have Their Say . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Adding a Wee Bit o’ Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
The Kind of Pop-Ups You Like . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
CHAPTER 18 Accessing Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
You and the Horse You Rode in On . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Readin’ ’n’ Writin’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
CHAPTER 19 Working with Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
The Resource Lineup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
String Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
Plain Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
String Formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
Styled Text. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
Styled Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Get the Picture? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
XML: The Resource Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
Miscellaneous Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Colors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Different Strokes for Different Folks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
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CHAPTER 20 Managing and Accessing Local Databases . . . . . . . . . . . . . 193
A Quick SQLite Primer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Start at the Beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
Setting the Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
Makin’ Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
What Goes Around Comes Around . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
Raw Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
Regular Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Building with Builders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Using Cursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
Making Your Own Cursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Data, Data, Everywhere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
CHAPTER 21 Leveraging Java Libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
The Outer Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
Ants and JARs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
Following the Script . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
. . . And Not a Drop to Drink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
CHAPTER 22 Communicating via the Internet . . . . . . . . . . . . . . . . . . . . . . . . . 207
REST and Relaxation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
HTTP Operations via Apache HttpComponents . . . . . . . . . . . . . . . . 207
Parsing Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
Stuff to Consider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
PART 4 ■ ■ ■ Intents
CHAPTER 23 Creating Intent Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
What’s Your Intent? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Pieces of Intents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Intent Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Stating Your Intent(ions) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Narrow Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
The Pause Caveat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
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CHAPTER 24 Launching Activities and Sub-Activities . . . . . . . . . . . . . . . . 221
Peers and Subs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Start ’Em Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Make an Intent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Make the Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Tabbed Browsing, Sort Of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
CHAPTER 25 Finding Available Actions via Introspection . . . . . . . . . . . . 231
Pick ’Em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
Would You Like to See the Menu? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Asking Around . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
CHAPTER 26 Handling Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
A Philosophy of Destruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
It’s All The Same, Just Different . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Now With More Savings! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
DIY Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Forcing the Issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Making Sense of it All . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
PART 5 ■ ■ ■ Content Providers and Services
CHAPTER 27 Using a Content Provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Pieces of Me . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Getting a Handle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Making Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Adapting to the Circumstances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
Doing It By Hand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Getting Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Give and Take . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Beware of the BLOB! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
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CHAPTER 28 Building a Content Provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
First, Some Dissection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Next, Some Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
Step #1: Create a Provider Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
onCreate() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
query() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
insert() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
update() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
delete(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
getType() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
Step #2: Supply a Uri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Step #3: Declare the Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Step #4: Update the Manifest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Notify-on-Change Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
CHAPTER 29 Requesting and Requiring Permissions . . . . . . . . . . . . . . . . . 269
Mother, May I? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Halt! Who Goes There? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Enforcing Permissions via the Manifest. . . . . . . . . . . . . . . . . . . . . . 271
Enforcing Permissions Elsewhere. . . . . . . . . . . . . . . . . . . . . . . . . . . 272
May I See Your Documents? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
CHAPTER 30 Creating a Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Service with Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
When IPC Attacks! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
Write the AIDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
Implement the Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
Manifest Destiny . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
Lobbing One Over the Fence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Where’s the Remote? And the Rest of the Code? . . . . . . . . . . . . . . . . . . 278
CHAPTER 31 Invoking a Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Bound for Success . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Request for Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Prometheus Unbound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Manual Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Catching the Lob . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
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CHAPTER 32 Alerting Users via Notifications . . . . . . . . . . . . . . . . . . . . . . . . . 285
Types of Pestering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
Hardware Notifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
Icons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
Seeing Pestering in Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
PART 6 ■ ■ ■ Other Android Capabilities
CHAPTER 33 Accessing Location-Based Services . . . . . . . . . . . . . . . . . . . . 293
Location Providers: They Know Where You’re Hiding . . . . . . . . . . . . . . . 293
Finding Yourself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
On the Move . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
Are We There Yet? Are We There Yet? Are We There Yet? . . . . . . . . . . 296
Testing...Testing... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
CHAPTER 34 Mapping with MapView and MapActivity . . . . . . . . . . . . . . . 299
Terms, Not of Endearment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
The Bare Bones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
Exercising Your Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
Zoom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
Center. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
Rugged Terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
Layers Upon Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
Overlay Classes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
Drawing the ItemizedOverlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
Handling Screen Taps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
My, Myself, and MyLocationOverlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
The Key to It All . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
CHAPTER 35 Handling Telephone Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
Report to the Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
You Make the Call! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
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CONTENTS
CHAPTER 36 Searching with SearchManager . . . . . . . . . . . . . . . . . . . . . . . . . 313
Hunting Season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
Search Yourself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
Craft the Search Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
Update the Manifest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
Searching for Meaning in Randomness . . . . . . . . . . . . . . . . . . . . . . . . . . 320
CHAPTER 37 Development Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Hierarchical Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Delightful Dalvik Debugging Detailed, Demoed . . . . . . . . . . . . . . . . . . . . 327
Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
File Push and Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
Screenshots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
Location Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
Placing Calls and Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
Put it On My Card . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
Creating a Card Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
Inserting the Card . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
CHAPTER 38 Where Do We Go from Here? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
Questions. Sometimes with Answers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
Heading to the Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
Getting Your News Fix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
APPENDIX Introducing Android 1.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
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About the Author
MARK MURPHY is the founder of CommonsWare and the author of the
Busy Coders Guide to Android Development. A three-time entrepreneur,
his experience ranges from consulting on open source and collaborative
development for the Fortune 500 to application development on just
about anything smaller than a mainframe. He has been a software devel-
oper for over 25 years, from the TRS-80 to the latest crop of mobile devices.
A polished speaker, Mr. Murphy has delivered conference presenta-
tions and training sessions on a wide array of topics internationally.
Mr. Murphy writes the BuildingDroids column for AndroidGuys and
the Android Angle column for NetworkWorld.
Outside of CommonsWare, Mr. Murphy has an avid interest in how the Internet will play a
role in citizen involvement with politics and government. He is also a contributor to the Reboo-
ting America essay collection.
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Acknowledgments
I would like to thank the Android team, not only for putting out a good product, but for invalu-
able assistance on the Android Google Groups. In particular, I would like to thank Romain Guy,
Justin Mattson, Dianne Hackborn, Jean-Baptiste Queru, Jeff Sharkey, and Xavier Ducrohet.
Icons used in the sample code were provided by the Nuvola
1
icon set.
1. http://www.icon-king.com/?p=15
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Introduction
Welcome to the Book!
Thanks for your interest in developing applications for Android! Increasingly, people will access
Internet-based services using so-called “non-traditional” means, such as mobile devices. The
more we do in that space now, the more that people will help invest in that space to make it
easier to build more powerful mobile applications in the future. Android is new—Android-powered
devices appeared on the scene first in late 2008—but it likely will rapidly grow in importance
due to the size and scope of the Open Handset Alliance.
Most of all, thanks for your interest in this book! I sincerely hope you find it useful and at
least occasionally entertaining.
Prerequisites
If you are interested in programming for Android, you will need at least basic understanding of
how to program in Java. Android programming is done using Java syntax, plus a class library
that resembles a subset of the Java SE library (plus Android-specific extensions). If you have not
programmed in Java before, you probably should learn how that works before attempting to
dive into programming for Android.
The book does not cover in any detail how to download or install the Android development
tools, either the Eclipse IDE flavor or the standalone flavor. The Android Web site
2
covers this
quite nicely. The material in the book should be relevant whether you use the IDE or not. You
should download, install, and test out the Android development tools from the Android Web
site before trying any of the examples listed in this book.
Editions of This Book
This book is being produced via a partnership between Apress and CommonsWare. You are
reading the Apress edition, which is available in print and in digital form from various digital
book services.
CommonsWare continually updates the original material and makes it available to members
of its Warescription program, under the title The Busy Coder’s Guide to Android Development.
CommonsWare maintains a FAQ about this partnership at http://commonsware.com/apress.
2. http://code.google.com/android/index.html
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INTRODUCTION
Source Code License
The source code samples shown in this book are available for download from the Apress Web
site.
3
All of the Android projects are licensed under the Apache 2.0 License
4
, in case you have
the desire to reuse any of it.
3. http://www.apress.com/book/view/1430224193
4. http://www.apache.org/licenses/LICENSE-2.0.html
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■ ■ ■
PART 1
Core Concepts
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■ ■ ■
CHAPTER 1
The Big Picture
Android devices, by and large, will be mobile phones. While the Android technology is being
discussed for use in other areas (e.g., car dashboard “PCs”), for the most part, you can think of
Android as being used on phones.
For developers, this has benefits and drawbacks.
On the plus side, circa 2009, Android-style smartphones are sexy. Offering Internet services
over mobile devices dates back to the mid-1990s and the Handheld Device Markup Language
(HDML). However, only in recent years have phones capable of Internet access taken off. Now,
thanks to trends like text messaging and to products like Apple’s iPhone, phones that can serve
as Internet access devices are rapidly gaining popularity. So, working on Android applications
gives you experience with an interesting technology (Android) in a fast-moving market segment
(Internet-enabled phones), which is always a good thing.
The problem comes when you actually have to program the darn things.
Anyone with experience in programming for PDAs or phones has felt the pain of phones
simply being small in all sorts of dimensions:
Screens are small (you won’t get comments like, “Is that a 24-inch LCD in your pocket,
or . . .?”).
Keyboards, if they exist, are small.
Pointing devices, if they exist, are annoying (as anyone who has lost their stylus will tell
you) or inexact (large fingers and “multi-touch” LCDs are not a good mix).
CPU speed and memory are tight compared to desktops and servers you may be used to.
You can have any programming language and development framework you want, so
long as it was what the device manufacturer chose and burned into the phone’s silicon.
And, so on . . .
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CHAPTER 1
THE BIG PICTURE
Moreover, applications running on a phone have to deal with the fact that they’re on a phone.
People with mobile phones tend to get very irritated when their phones don’t work, which
is why the “Can you hear me now?” ad campaign from Verizon Wireless has been popular for
the past few years. Similarly, those same people will get irritated at you if your program “breaks”
their phone by
tying up the CPU so that calls can’t be received
not working properly with the rest of the phone’s OS, such that your application doesn’t
quietly fade to the background when a call comes in or needs to be placed
crashing the phone’s operating system, such as by leaking memory like a sieve
Hence, developing programs for a phone is a different experience than developing desktop
applications, Web sites, or back-end server processes. You wind up with different-looking
tools, different-behaving frameworks, and “different than you’re used to” limitations on what
you can do with your program.
What Android tries to do is meet you halfway:
You get a commonly-used programming language (Java) with some commonly used
libraries (e.g., some Apache Commons APIs) along with support for tools you may be
used to (Eclipse).
You get a fairly rigid and separate framework in which your programs need to run so they
can be “good citizens” on the phone and not interfere with other programs or the oper-
ation of the phone itself.
As you may expect, much of this book deals with that framework and how you write programs
that work within its confines and take advantage of its capabilities.
What Androids Are Made Of
When you write a desktop application, you are “master of your own domain.” You launch your
main window and any child windows—like dialog boxes—that are needed. From your stand-
point, you are your own world, leveraging features supported by the operating system, but
largely ignorant of any other program that may be running on the computer at the same time.
If you do interact with other programs, it is typically through an API, such as using JDBC (or
frameworks atop it) to communicate with MySQL or another database.
Android has similar concepts, but packaged differently, and structured to make phones
more crash-resistant.
Activities
The building block of the user interface is the activity. You can think of an activity as being the
Android analogue for the window or dialog in a desktop application.
While it is possible for activities to not have a user interface, most likely your “headless”
code will be packaged in the form of content providers or services, like the following described.
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CHAPTER 1 THE BIG PICTURE
5
Content Providers
Content providers provide a level of abstraction for any data stored on the device that is acces-
sible by multiple applications. The Android development model encourages you to make your
own data available to other applications, as well as your own—building a content provider lets
you do that, while maintaining complete control over how your data gets accessed.
Intents
Intents are system messages, running around the inside of the device, notifying applications of
various events, from hardware state changes (e.g., an SD card was inserted), to incoming data
(e.g., an SMS message arrived), to application events (e.g., your activity was launched from the
device’s main menu). Not only can you respond to intents, but you can create your own, to
launch other activities, or to let you know when specific situations arise (e.g., raise such-and-
so intent when the user gets within 100 meters of this-and-such location).
Services
Activities, content providers, and intent receivers are all short-lived and can be shut down at
any time. Services, on the other hand, are designed to keep running, if needed, independent of
any activity. You might use a service for checking for updates to an RSS feed, or to play back
music even if the controlling activity is no longer operating.
Stuff at Your Disposal
Android comes with a number of features to help you develop applications.
Storage
You can package data files with your application, for things that do not change, such as icons
or help files. You also can carve out a small bit of space on the device itself, for databases or files
containing user-entered or retrieved data needed by your application. If the user supplies bulk
storage, like an SD card, you can read and write files on there as needed.
Network
Android devices will generally be Internet-ready, through one communications medium or
another. You can take advantage of the Internet access at any level you wish, from raw Java
sockets all the way up to a built-in WebKit-based Web browser widget you can embed in your
application.
Multimedia
Android devices have the ability to play back and record audio and video. While the specifics
may vary from device to device, you can query the device to learn its capabilities and then take
advantage of the multimedia capabilities as you see fit, whether that is to play back music, take
pictures with the camera, or use the microphone for audio note-taking.
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GPS
Android devices will frequently have access to location providers, such as GPS, that can tell
your applications where the device is on the face of the Earth. In turn, you can display maps or
otherwise take advantage of the location data, such as tracking a device’s movements if the
device has been stolen.
Phone Services
Of course, Android devices are typically phones, allowing your software to initiate calls, send
and receive SMS messages, and everything else you expect from a modern bit of telephony
technology.
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