Android Recipes: A Problem-Solution Approach

451 Pages·2011·9.23 MB·English

by  Dave Smith

Companion
eBooCkompanion
eBook
Available 488 CHAPTER 9: Super Jumper: A 2D OpenGL ES Game
Available
Your reference guide for rapidly understanding Android
Your reference guide for rapidly understanding Android
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Approach take the time and stress out of developing top-notch apps for this A
Approach take the time and stress out of developing top-notch apps for this
leading mobile OS platform. When you start a new project, just copy and paste
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Using complete and tested code examples, Android Recipes features a host of d
Using complete and tested code examples, Android Recipes features a host of d
solutions to practical problems. Study it chapter by chapter, or dip into its more
solutions to practical problems. Study it chapter by chapter, or dip into its more
than 80 down-to-earth recipes to find the exact solution you need as you need it.
than 80 down-to-earth recipes to find the exact solution you need as you need it. r
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Android Recipes teaches you how to build an app with Google’s Android SDK at o
Android Recipes teaches you how to build an app with Google’s Android SDK at o
the command line or the graphical Eclipse IDE. From there, you’ll rapidly master
the command line or the graphical Eclipse IDE. From there, you’ll rapidly master
the user interface, cloud communications, device hardware, data persistence, i
the user interface, cloud communications, device hardware, data persistence, i
inter-app communications, and interaction with Android itself. d
inter-app communications, and interaction with Android itself. d
What you’ll learn
• AnWdrh•oa itd y aorcuh’lilt leecatrunre and various Android-specific APIs R
• Android architecture and various Android-specific APIs R
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How to develop a Units Converter app in the context of command-line/
Android SDK and Eclipse/Android SDK environments
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From insightful instruction to helpful examples, Android Recipes is your guide to e
From insightful instruction to helpful examples, Android Recipes is your guide to e
writing cool, popular apps for one of today’s hottest mobile platforms. Android Recipes
writing cool, popular apps for one of today’s hottest mobile platforms. Android Recipes
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A Problem-Solution Approach
A Problem-Solution Approach
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488 CHAPTER 9: Super Jumper: A 2D OpenGL ES Game
For your convenience Apress has placed some of the front
matter material after the index. Please use the Bookmarks
and Contents at a Glance links to access them.
Contents at a Glance
Contents ............................................................................................................. iv
Foreword ......................................................................................................... viii
About the Authors .............................................................................................. ix
About the Technical Reviewer ............................................................................ x
Acknowledgments ............................................................................................. xi
Preface ............................................................................................................. xii
■Chapter 1: Getting Started with Android ......................................................... 1(cid:1)
■Chapter 2: User Interface Recipes ................................................................. 75(cid:1)
■Chapter 3: Communications and Networking .............................................. 155(cid:1)
■Chapter 4: Interacting with Device Hardware and Media ........................... 201(cid:1)
■Chapter 5: Persisting Data .......................................................................... 257(cid:1)
■Chapter 6: Interacting with the System ...................................................... 309(cid:1)
■Chapter 7: Working with Libraries .............................................................. 353(cid:1)
■Appendix A: Scripting Layer for Android ..................................................... 385(cid:1)
■Appendix B: Android NDK ............................................................................ 397(cid:1)
■Appendix C: App Design Guidelines ............................................................. 411(cid:1)
Index ............................................................................................................... 419
iii
1
1
Chapter
Getting Started with
Android
Android is hot, and many people are developing Android applications (apps for short).
Perhaps you would also like to develop apps, but are unsure about how to get started.
Although you could study Google’s online Android Developer’s Guide
(http://developer.android.com/guide/index.html) to acquire the needed knowledge,
you might be overwhelmed by the vast amount of information that this guide presents. In
contrast, this chapter provides just enough theory to help you understand the basics of
Android. This theory is followed by several recipes that teach you how to develop apps
and prepare them for publication to Google’s Android Market.
What Is Android?
The Android Developer’s Guide defines Android as a software stack – a set of software
subsystems needed to deliver a fully functional solution – for mobile devices. This stack
includes an operating system (a modified version of the Linux kernel), middleware
(software that connects the low-level operating system to high-level apps) that’s partly
based on Java, and key apps (written in Java) such as a web browser (known as
Browser) and a contact manager (known as Contacts).
Android offers the following features:
(cid:1) Application framework enabling reuse and replacement of app
components (discussed later in this chapter)
(cid:1) Bluetooth, EDGE, 3G, and WiFi support (hardware dependent)
(cid:1) Camera, GPS, compass, and accelerometer support (hardware
dependent)
(cid:1) Dalvik Virtual Machine (DVM) optimized for mobile devices
(cid:1) GSM Telephony support (hardware dependent)

1
2 CHAPTER 1: Getting Started with Android
(cid:1) Integrated browser based on the open source WebKit engine
(cid:1) Media support for common audio, video, and still image formats
(MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
(cid:1) Optimized graphics powered by a custom 2D graphics library; 3D
graphics based on the OpenGL ES 1.0 specification (hardware
acceleration optional)
(cid:1) SQLite for structured data storage
Although not part of an Android device’s software stack, Android’s rich development
environment (including a device emulator and a plugin for the Eclipse IDE) could also be
considered an Android feature.
History of Android
Contrary to what you might expect, Android did not originate with Google. Instead,
Android was initially developed by Android, Inc., a small Palo Alto, California-based
startup company. Google bought this company in July 2005 and released a preview
version of the Android SDK in November 2007.
In mid-August, 2008, Google released the Android 0.9 SDK beta, and subsequently
released the Android 1.0 SDK one month later. Table 1–1 outlines subsequent SDK
update releases. (Starting with version 1.5, each major release comes under a code
name that’s based on a dessert item.)
Table 1–1. Android Update Releases
SDK Update Release Date and Changes
1.1 Google released SDK 1.1 on February 9, 2009. Changes included paid apps
(via Android Market) and “search by voice” support.
1.5 (Cupcake) Google released SDK 1.5 on April 30, 2009. Changes included the ability to
Based on Linux record and watch videos through camcorder mode, the ability to upload
Kernel 2.6.27 videos to YouTube and pictures to Picasa, the ability to populate the home
screen with widgets, and animated screen transitions.
1.6 (Donut) Google released SDK 1.6 on September 15, 2009. Changes included an
Based on Linux improved Android Market experience, an integrated
Kernel 2.6.29 camera/camcorder/gallery interface, updated “search by voice” with speed
and other improvements, and an updated search experience.
2.0/2.1 (Eclair) Google released SDK 2.0 on October 26, 2009. Changes included a
Based on Linux revamped user interface, a new contacts list, support for Microsoft
Kernel 2.6.29 Exchange, digital zoom, improved Google Maps (version 3.1.2), HTML5
support for the Browser app, live wallpapers, and Bluetooth 2.1 support.
Google subsequently released SDK update 2.0.1 on December 3, 2009, and
SDK update 2.1 on January 12, 2010.
CHAPTER 1: Getting Started with Android 3
SDK Update Release Date and Changes
2.2 (Froyo) Google released SDK 2.2 on May 20, 2009. Changes included the
Based on Linux integration of Chrome’s V8 JavaScript engine into the Browser app, voice
Kernel 2.6.32 dialing and contact sharing over Bluetooth, Adobe Flash 10.1 support,
additional app speed improvements courtesy of a JIT implementation, and
USB tethering and WiFi hotspot functionality.
2.3 (Gingerbread) Google released SDK 2.3 on December 6, 2010. Changes included a new
Based on Linux concurrent garbage collector that improves an app’s responsiveness,
Kernel 2.6.35.7 support for gyroscope sensing, support for WebM video playback and other
video improvements, support for near field communication, and improved
social networking features. This book focuses on Android 2.3.
Google subsequently released SDK 2.3.1 to fix some bugs, and SDK 2.3.3,
a small feature release that adds several improvements and APIs to the
Android 2.3 platform.
3.0 (Honeycomb) Google released SDK 3.0 on February 22, 2011. Unlike previous releases,
Based on Linux version 3.0 focuses exclusively on tablets, such as Motorola Zoom, the first
2.6.36 tablet to be released (on February 24, 2011). In addition to an improved
user interface, version 3.0 improves multitasking, supports multicore
processors, supports hardware acceleration, and provides a 3D desktop
with redesigned widgets.
Android Architecture
The Android software stack consists of apps at the top, middleware (consisting of an
application framework, libraries, and the Android runtime) in the middle, and a Linux
kernel with various drivers at the bottom. Figure 1–1 shows this layered architecture.
4 CHAPTER 1: Getting Started with Android

Figure 1–1. Android’s layered architecture consists of several major parts.
Users care about apps, and Android ships with a variety of useful core apps, which
include Browser, Contacts, and Phone. All apps are written in the Java programming
language. Apps form the top layer of Android’s architecture.
Directly beneath the app layer is the application framework, a set of high-level building
blocks for creating apps. The application framework is preinstalled on Android devices
and consists of the following components:
(cid:1) Activity Manager: This component provides an app’s lifecycle and
maintains a shared activity stack for navigating within and among
apps. Both topics are discussed later in this chapter.
(cid:1) Content Providers: These components encapsulate data (such as the
Browser app’s bookmarks) that can be shared among apps.
(cid:1) Location Manager: This component makes it possible for an Android
device to be aware of its physical location.
CHAPTER 1: Getting Started with Android 5
(cid:1) Notification Manager: This component lets an app notify the user of a
significant event (such as a message’s arrival) without interrupting
what the user is currently doing.
(cid:1) Package Manager: This component lets an app learn about other app
packages that are currently installed on the device. (App packages are
discussed later in this chapter.)
(cid:1) Resource Manager: This component lets an app access its resources,
a topic that’s briefly discussed in Recipe 1–5.
(cid:1) Telephony Manager: This component lets an app learn about a
device’s telephony services. It also handles making and receiving
phone calls.
(cid:1) View System: This component manages user interface elements and
user interface-oriented event generation. (These topics are briefly
discussed in Recipe 1–5.)
(cid:1) Window Manager: This component organizes the screen’s real estate
into windows, allocates drawing surfaces, and performs other window-
related jobs.
The components of the application framework rely on a set of C/C++ libraries to perform
their jobs. Developers interact with the following libraries by way of framework APIs:
(cid:1) FreeType: This library supports bitmap and vector font rendering.
(cid:1) libc: This library is a BSD-derived implementation of the standard C
system library, tuned for embedded Linux-based devices.
(cid:1) LibWebCore: This library offers a modern and fast web browser engine
that powers the Android browser and an embeddable web view. It’s
based on WebKit (http://en.wikipedia.org/wiki/WebKit) and is also
used by the Google Chrome and Apple Safari browsers.
(cid:1) Media Framework: These libraries, which are based on PacketVideo’s
OpenCORE, support the playback and recording of many popular
audio and video formats, as well as working with static image files.
Supported formats include MPEG4, H.264, MP3, AAC, AMR, JPEG,
and PNG.
(cid:1) OpenGL | ES: These 3D graphics libraries provide an OpenGL
implementation based on OpenGL | ES 1.0 APIs. They use hardware
3D acceleration (where available) or the included (and highly
optimized) 3D software rasterizer.
(cid:1) SGL: This library provides the underlying 2D graphics engine.
(cid:1) SQLite: This library provides a powerful and lightweight relational
database engine that’s available to all apps, and that’s also used by
Mozilla Firefox and Apple’s iPhone for persistent storage.
6 CHAPTER 1: Getting Started with Android
(cid:1) SSL: This library provides secure sockets layer-based (SSL-based)
security for network communication.
(cid:1) Surface Manager: This library manages access to the display
subsystem, and seamlessly composites 2D and 3D graphic layers from
multiple apps.
Android provides a runtime environment that consists of core libraries (implementing a
subset of the Apache Harmony Java version 5 implementation) and the Dalvik Virtual
Machine (DVM), a non-Java virtual machine that’s based on processor registers instead
of being stack-based.
NOTE: Google’s Dan Bornstein created Dalvik and named this virtual machine after an Icelandic
fishing village where some of his ancestors lived.
Each Android app defaults to running in its own Linux process, which hosts an instance
of Dalvik. This virtual machine has been designed so that devices can run multiple virtual
machines efficiently. This efficiency is largely due to Dalvik executing Dalvik Executable
(DEX)-based files – DEX is a format that’s optimized for a minimal memory footprint.
NOTE: Android starts a process when any of part of the app needs to execute, and shuts down
the process when it’s no longer needed and system resources are required by other apps.
Perhaps you’re wondering how it’s possible to have a non-Java virtual machine run Java
code. The answer is that Dalvik doesn’t run Java code. Instead, Android transforms
compiled Java classfiles into the DEX format, and it’s this resulting code that gets
executed by Dalvik.
Finally, the libraries and Android runtime rely on the Linux kernel (version 2.6) for
underlying core services such as threading, low-level memory management, a network
stack, process management, and a driver model. Furthermore, the kernel acts as an
abstraction layer between the hardware and the rest of the software stack.
ANDROID SECURITY MODEL
Android’s architecture includes a security model that prevents apps from performing operations considered
harmful to other apps, Linux, or users. This security model, which is mostly based on process level
enforcement via standard Linux features (such as user and group IDs), places processes in a security
sandbox.
By default, the sandbox prevents apps from reading or writing the user’s private data (such as contacts or
emails), reading or writing another app’s files, performing network access, keeping the device awake,
accessing the camera, and so on. Apps that need to access the network or perform other sensitive
operations must first obtain permission to do so.
CHAPTER 1: Getting Started with Android 7
Android handles permission requests in various ways, typically by automatically allowing or disallowing the
request based upon a certificate, or by prompting the user to grant or revoke the permission. Permissions
required by an app are declared in the app’s manifest file (discussed later in this chapter) so that they are
known to Android when the app is installed. These permissions won’t subsequently change.
App Architecture
The architecture of an Android app differs from desktop application architecture. App
architecture is based upon components that communicate with each other by using
intents that are described by a manifest and that are stored in an app package.
Components
An app is a collection of components (activities, services, content providers, and
broadcast receivers) that run in a Linux process and that are managed by Android.
These components share a set of resources, including databases, preferences, a
filesystem, and the Linux process.
NOTE: Not all of these components need to be present in an app. For example, one app might
consist of activities only, whereas another app might consist of activities and a service.
This component-oriented architecture lets an app reuse the components of other apps,
provided that those other apps permit reuse of their components. Component reuse
reduces overall memory footprint, which is very important for devices with limited
memory.
To make the reuse concept concrete, suppose you’re creating a drawing app that lets
users choose a color from a palette, and suppose that another app has developed a
suitable color chooser and permits this component to be reused. In this scenario, the
drawing app can call upon that other app’s color chooser to have the user select a color
rather than provide its own color chooser. The drawing app doesn’t contain the other
app’s color chooser or even link to this other app. Instead, it starts up the other app’s
color chooser component when needed.
Android starts a process when any part of the app (such as the aforementioned color
chooser) is needed, and instantiates the Java objects for that part. This is why Android’s
apps don’t have a single entry point (no C-style main() function, for example). Instead,
apps use components that are instantiated and run as needed.
Activities
An activity is a component that presents a user interface so that the user can interact
with an app. For example, Android’s Contacts app includes an activity for entering a