Android开发者必读：《The Android Developers Cookbook》详解

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"The Android Developer's Cookbook" 是一本专为Android开发人员编写的经典指南，旨在帮助读者通过Android SDK构建应用程序。这本书共有339页，深入浅出地讲解了Android应用开发的各种技术和实践。作者James Steele和Nelson To以其丰富的经验和专业知识，为读者提供了从入门到进阶的全方位指导，涵盖了Android平台的基础架构、API使用、界面设计、性能优化以及与硬件交互等方面的知识。在本书中，读者可以学习到如何利用Android SDK的工具和框架，如Activity、Service、BroadcastReceiver和Content Provider等核心组件来构建功能丰富的应用程序。此外，书中还特别强调了适应Android系统的多样性，包括处理不同版本的兼容性问题，以及如何创建适应各种屏幕尺寸和分辨率的应用。作为一本权威的“开发宝典”，《The Android Developer's Cookbook》不仅提供理论知识，还包括了大量的实战案例和示例代码，使得学习者能够迅速上手并加深理解。作者在编写过程中，充分考虑了实际开发中的挑战和可能遇到的问题，以便读者能够从中获益。尽管作者和出版社对书中的内容进行了精心准备，但必须指出的是，它并非一本无懈可击的教科书，存在一些可能的错误或遗漏。因此，读者在使用时应保持批判性思维，并在必要时查阅官方文档和社区资源来验证信息。同时，书中并不承担因使用其中信息或程序导致的偶然或间接损害的责任。对于批量购买或特殊销售，该出版商提供了优惠，包括电子版和定制选项，这为机构和个人开发者提供了灵活的学习选择。《The Android Developer's Cookbook》是Android开发者不可或缺的参考资料，无论是新手还是经验丰富的开发者，都能从中受益匪浅。

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About the Authors

James Steele was doing post-doctoral work in physics at MIT when he decided to join

a startup in Silicon Valley. Fifteen years later and he continues to innovate, bringing

research projects to production in both the consumer and mobile market. He actively

presents and participates in various Silicon Valley new technology groups.

Nelson To has more than ten applications of his own in the Android Market. He also has

worked on enterprise Android applications for Think Computer, Inc. (PayPhone), AOL

(AIM), Stanford University (Education App), and Logitech (Google TV). He also assists

in organizing the Silicon Valley Android Meetup Community and teaches Android classes

both in the Bay Area and China.

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Overview of Android

The Android operating system (OS) has come a long way since the announcement of

the Open Handset Alliance in late 2007.The idea of an open source OS for embedded

systems was not new, but Google aggressively backing it definitely has helped push

Android to the forefront in just a few years.

Many wireless carriers in multiple countries across various communication protocols

have one or more Android phones available. Other embedded devices, such as tablets, net-

books, televisions, set-top boxes, and even automobiles, have also adopted the Android OS.

This chapter discusses various general aspects of Android useful for a developer. It pro-

vides a foundation for the creation of Android applications and a context for the recipes

in the rest of this book.

The Evolution of Android

Google, seeing a large growth of Internet use and search in mobile devices, acquired

Android, Inc., in 2005 to focus its development on a mobile device platform.Apple intro-

duced the iPhone in 2007 with some ground-breaking ideas including multitouch and an

open market for applications.Android was quickly adapted to include these features and

to offer definite distinctions, such as more control for developers and multitasking. In

addition,Android incorporates enterprise requirements, such as exchange support, remote

wipe, and Virtual Private Network (VPN) support, to go after the enterprise market that

Research In Motion has developed and held so well with its Blackberry models.

Device diversity and quick adaptation have helped Android grow its user base, but it

comes with potential challenges for developers.Applications need to support multiple

screen sizes, resolution ratios, keyboards, hardware sensors, OS versions, wireless data rates,

and system configurations. Each can lead to different and unpredictable behavior, but test-

ing applications across all environments is an impossible task.

Android has therefore been constructed to ensure as uniform an experience across

platforms as possible. By abstracting the hardware differences,Android OS tries to insulate

applications from device-specific modifications while providing the flexibility to tune

aspects as needed. Future-proofing of applications to the introduction of new hardware

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Chapter 1 Overview of Android

platforms and OS updates is also a consideration.This mostly works as long as the devel-

oper is well aware of this systematic approach.The generic Application Programming

Interfaces (API) that Android offers and how to ensure device and OS compatibility are

main threads discussed throughout this book.

Still, as with any embedded platform, extensive testing of applications is required.

Google provides assistance to third-party developers in many forms as Android Develop-

ment Tool (ADT) plugins for Eclipse (also as standalone tools) including real-time log-

ging capabilities, a realistic emulator that runs native ARM code, and in-field error reports

from users to developers of Android Market applications.

The Dichotomy of Android

Android has some interesting dichotomies. Knowing about them upfront is useful not

only in understanding what Android is, but what it is not.

Android is an embedded OS that relies on the Linux kernel for core system services,

but it is not embedded Linux. For example, standard Linux utilities such as X-windows

and GNU C libraries are not supported.Writing applications for Android utilizes the

Java framework, but it is not Java. Standard Java libraries such as Swing are not sup-

ported. Other libraries such as Timer are not preferred; they have been replaced by

Android’s own libraries, which are optimized for usage in a resource-constrained,

embedded environment.

The Android OS is open source, which means developers can view and use any of the

system source code, including the radio stack.This source code is one of the first

resources for seeing examples of Android code in action, and it helps clarify the usage

when documentation is lacking.This also means developers can utilize the system in the

same way as any core application and can swap out system components for their own

components. However,Android devices do contain some proprietary software that is

inaccessible to developers (such as Global Positioning System (GPS) navigation).

A final dichotomy of Android OS is that Google is also backing Chrome OS.Android

OS is built for embedded platforms, and Chrome OS is built for cloud-based platforms.

However, which is the best choice for embedded devices that live in the cloud? Net-

books, which fill the gap between smart phones and laptop computers, could presumably

go either way (and they have). Android has started to utilize the cloud more. Does that

mean Chrome OS’s days are numbered? Google also backs a web-based market, so

Chrome OS enjoys the same developer leverage that Android currently has.This points to

a convergence that might have been in the cards all along.

Devices Running Android

There are more than 40 Android phones in the market from more than ten manufactur-

ers. Other hardware also runs Android, such as tablets and televisions. Software can access

information on the target device using the android.os.Build class, for example:

if(android.os.Build.MODEL.equals("Nexus+One")) { ... }

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Devices Running Android

Android-supported hardware shares some common features due to the nature of the

operating system.The Android OS is organized into the following images:

Bootloader—Initiates loading of the boot image during startup

Boot image—Kernel and RAMdisk

System image—Android operating system platform and apps

Data image—User data saved across power cycles

Recovery image—Files used for rebuilding or updating the system

Radio image—Files of the radio stack

These images are stored on nonvolatile flash memory, so they are protected when the

device powers down.The flash memory is used like read-only memory (hence, some call

it ROM), but can it be rewritten as necessary (for example, with over-the-air Android

operating system updates).

On startup, the microprocessor executes the bootloader to load the kernel and

RAMdisk to RAM for quick access.The microprocessor then executes instructions and

pages portions of the system and data images into RAM as needed.The radio image

resides on the baseband processor, which connects to the radio hardware.

A comparison of some of the early and more recent smart phone models is shown in

Table 1.1. I t s h ow s tha t t h e p rocessin g h a rdwa re arc h i t e c ture i s s i m i l a r a c ross d ev ices : a

microprocessor unit (MPU), synchronous dynamic random access memory (SDRAM or

RAM for short), and flash memory (called ROM for short).The screen size is given in

pixels, but the dots per inch (dpi) vary depending on the physical screen size. For exam-

ple, the HTC Magic has a 3.2-inch diagonal screen with 320x480 pixels.This equates to

180 pixels per inch, but is classified as a medium pixel density device by Android (which

averages as 160 dpi).All smartphones also offer a CMOS image sensor camera, Bluetooth

(BT), and Wi-Fi (802.11), although there are variations.

Tab le 1 .1 Comparison of Some Representative Android Smartphones. Data from

http://en.wikipedia.org/wiki/List_of_Android_devices and http://pdadb.net/.

Model MPU

RAM/

ROM Screen Other Features

HTC Dream / G1

(October 2008)

528-MHz

QCOM

MSM7201A

192MB/

256MB

TFT LCD

320x480

mdpi

GSM/UMTS

slide out keyboard,

trackball, AGPS

BT2.0, 802.11b/g,

3.1-MP camera

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