精通Android 4：详细指南

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"Pro.Android 4 English" 这是一本面向初学者的Android开发指南，英文版的《Pro Android 4》。书中的内容深入浅出，相比其他同类中文入门书籍，可能更加易于理解和全面。该书涵盖了Android计算平台的介绍、开发环境的设置、Android资源的理解、内容提供者(Content Providers)、意图(Intents)、用户界面构建、菜单操作、针对平板设备的Fragments、对话框(Dialogs)的使用、ActionBar的探索、高级调试与分析、配置变化响应、偏好设置和状态保存、安全性和权限管理、服务的构建与消费、包的探索以及Handler的讲解等多方面的Android开发核心知识。在"关于作者"和"技术审阅者"的部分，读者可以了解到本书的作者团队和专家评审团的专业背景，为书籍的权威性提供了保证。"致谢"章节则表达了作者对参与书籍创作和提供帮助的所有人的感激之情。 "前言"部分可能概述了本书的编写目的、适用人群以及学习Android开发的重要性。书中各章节详细展开，从基础的Android平台介绍开始，引导读者逐步建立Android开发环境，理解资源管理机制，到掌握如何通过Intent进行应用间的交互，构建用户界面，以及处理多设备适配问题。此外，书中还涉及了Android应用的调试技巧，权限管理和安全性，服务的使用，以及包管理和消息处理机制，为读者提供了一套完整的Android开发知识体系。对于想要系统学习Android开发的初学者，这本书提供了丰富的实践案例和详尽的解释，有助于快速上手并深入理解Android平台的工作原理。同时，由于是英文版，对提高英文阅读能力也有一定帮助，适合有一定英语基础的开发者阅读。

CHAPTER 1: Introducing the Android Computing Platform

loaded as XML files and because resource IDs for those menus are auto-generated.

Here’s how you would declare menus in an XML file:

<item android:id="@+id/menu_clear"

android:orderInCategory="10"

android:title="clear" />

<item android:id="@+id/menu_show_browser"

android:orderInCategory="5"

android:title="show browser" />

</group>

</menu>

Android supports dialogs, and all dialogs in Android are asynchronous. These

asynchronous dialogs present a special challenge to developers accustomed to the

synchronous modal dialogs in some windowing frameworks. We’ll address menus in

Chapter 7 and dialogs in Chapter 9.

Android offers extensive support for animation. There are three fundamental ways to

accomplish animation. You can do frame-by-frame animation. Or you can provide

tweening animation by changing view transformation matrices (position, scale, rotation,

and alpha). Or you can also do tweening animation by changing properties of objects.

The property-based animation is introduced in 3.0 and is the most flexible and

recommended way to accomplish animation. All of these animations are covered in

Chapter 21.

Moreover, Android allows you to define these animations in an XML resource file. Check

out this example, in which a series of numbered images is played in frame-by-frame

animation:

<animation-list xmlns:android="http://schemas.android.com/apk/res/android"

android:oneshot="false">

……

</animation-list>

Android also supports 3D graphics through its implementation of the OpenGL ES 1.0

and 2.0 standards. OpenGL ES, like OpenGL, is a C-based flat API. The Android SDK,

because it’s a Java-based programming API, needs to use Java binding to access the

OpenGL ES. Java ME has already defined this binding through Java Specification

Request (JSR) 239 for OpenGL ES, and Android uses the same Java binding for

OpenGL ES in its implementation. If you are not familiar with OpenGL programming, the

learning curve is steep. Due to space limitations, we are not able to include the OpenGL

coverage in the fourth edition of the book. However we have over 100 pages of

coverage in our third edition.

Android has a number of new concepts that revolve around information at your fingertips

using the home screen. The first of these is live folders. Using live folders, you can

publish a collection of items as a folder on the homepage. The contents of this collection

change as the underlying data changes. This changing data could be either on the

CHAPTER 1: Introducing the Android Computing Platform

device or from the Internet. Due to space limitations, we are not able to cover live folders

in the fourth edition of the book. However, the third edition includes extensive coverage.

The second homepage-based idea is the home screen widget. Home screen widgets are

used to paint information on the homepage using a UI widget. This information can

change at regular intervals. An example could be the number of e-mail messages in your

e-mail store. We describe home screen widgets in Chapter 25. The home screen

widgets are enhanced in 3.0 to include list views that can get updated when their

underlying data changes. These enhancements are covered in Chapter 26.

Integrated Android Search is the third homepage-based idea. Using integrated search,

you can search for content both on the device and also across the Internet. Android

search goes beyond search and allows you to fire off commands through the search

control. Due to space limitations, we can’t include coverage of the search API in the

fourth edition of the book. However, it is covered in the third edition.

Android also supports touchscreen and gestures based on finger movements on the

device. Android allows you to record any random motion on the screen as a named

gesture. This gesture can then be used by applications to indicate specific actions. We

cover touchscreens and gestures in Chapter 27.

Sensors are now becoming a significant part of the mobile experience. We cover

sensors in Chapter 29.

Another necessary innovation required for a mobile device is the dynamic nature of its

configurations. For instance, it is very easy to change the viewing mode of a handheld

between portrait and landscape. Or you may dock your handheld to become a laptop.

Android 3.0 has introduced a concept called fragments to deal with these variations

effectively. Chapter 8 is dedicated to fragments, and Chapter 12 talks about how to deal

with configuration changes.

We also cover the 3.0 feature (which is much enhanced in 4.0) of action bars in Chapter 10.

Action bars bring Android up to par with a desktop menu bar paradigm.

Drag-and-drop is introduced for tablets in 3.0. This feature is now available to phones as

well. We cover drag-and-drop in Chapter 28.

Handheld devices are fully aware of a cloud-based environment. To make server-side

HTTP calls, it is important to understand the threading model to avoid Application Not

Responding messages. We cover the mechanisms available for asynchronous

processing in Chapter 18.

Outside of the Android SDK, there are a number of independent innovations taking place

to make development exciting and easy. Some examples are XML/VM, PhoneGap, and

Titanium. Titanium allows you to use HTML technologies to program the WebKit-based

Android browser. We covered Titanium in the second edition of this book. However, due

to time and space limitations, we are not covering Titanium in this edition.

CHAPTER 1: Introducing the Android Computing Platform

Android Service Components

Security is a fundamental part of the Android platform. In Android, security spans all

phases of the application life cycle—from design-time policy considerations to runtime

boundary checks. We cover security and permissions in Chapter 14.

In Chapter 15, we’ll show you how to build and consume services in Android,

specifically HTTP services. This chapter will also cover interprocess communication

(communication between applications on the same device).

Location-based service is another of the more exciting components of the Android SDK.

This portion of the SDK provides application developers with APIs to display and

manipulate maps, as well as obtain real-time device-location information. We’ll cover

these ideas in detail in Chapter 22.

Android Media and Telephony Components

Android has APIs that cover audio, video, and telephony components. Chapter 23 will

address the telephony API. We’ll cover the audio and video APIs extensively in

Chapter 24.

Starting with Android 2.0, Android includes the Pico Text-to-Speech engine. Due to

space limitations, we are not able to include Text-to-Speech coverage in the fourth

edition of the book. The third edition does cover the Text-to-Speech API.

Last but not least, Android ties all these concepts into an application by creating a single

XML file that defines what an application package is. This file is called the application’s

manifest file (AndroidManifest.xml). Here is an example:

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="com.ai.android.HelloWorld"

android:versionCode="1"

android:versionName="1.0.0">

<activity android:name=".HelloWorld"

android:label="@string/app_name">

<intent-filter>

</intent-filter>

</activity>

</application>

</manifest>

The Android manifest file is where activities are defined, where services and content

providers are registered, and where permissions are declared. Details about the

manifest file will emerge throughout the book as we develop each idea.

CHAPTER 1: Introducing the Android Computing Platform

Android Java Packages

One way to get a quick snapshot of the Android platform is to look at the structure of

Java packages. Because Android deviates from the standard JDK distribution, it is

important to know what is supported and what is not. Here’s a brief description of the

important packages that are included in the Android SDK:

android.app: Implements the Application model for Android. Primary

classes include Application, representing the start and stop

semantics, as well as a number of activity-related classes, fragments,

controls, dialogs, alerts, and notifications. We work with most of these

classes through out this book.

android.app.admin: Provides the ability to control the device by folks

such as enterprise administrators.

android.accounts: Provides classes to manage accounts such as

Google, Facebook, and so on. The primary classes are

AccountManager and Account. We cover this API briefly in Chapter 30

when we discuss the Contacts API.

android.animation: Hosts all the new property animation classes.

These clases are extensively covered in Chapter 21.

android.app.backup: Provides hooks for applications to back up and

restore their data when folks switch their devices.

android.appwidget: Provides functionality for home screen widgets.

This package is covered extensively in Chapter 25 and Chapter 26

when we talk about home screen widgets, including list-based

widgets.

android.bluetooth: Provides a number of classes to work with

Bluetooth functionality. The main classes include BluetoothAdapter,

BluetoothDevice, BluetoothSocket, BluetoothServerSocket, and

BluetoothClass. You can use BluetoothAdapter to control the locally

installed Bluetooth adapter. For example, you can enable it, disable it,

and start the discovery process. BluetoothDevice represents the

remote Bluetooth device that you are connecting with. The two

Bluetooth sockets are used to establish communication between the

devices. A Bluetooth class represents the type of Bluetooth device you

are connecting to.

android.content: Implements the concepts of content providers.

Content providers abstract out data access from data stores. This

package also implements the central ideas around intents and Android

Uniform Resource Identifiers (URIs). These classes are covered in

Chapter 4.

CHAPTER 1: Introducing the Android Computing Platform

android.content.pm: Implements package manager–related classes. A

package manager knows about permissions, installed packages,

installed providers, installed services, installed components such as

activities, and installed applications.

android.content.res: Provides access to resource files, both

structured and unstructured. The primary classes are AssetManager

(for unstructured resources) and Resources. Some of the classes from

this package are covered in Chapter 3.

android.database: Implements the idea of an abstract database. The

primary interface is the Cursor interface. Some of the classes from this

package are covered in Chapter 4.

android.database.sqlite: Implements the concepts from the

android.database package using SQLite as the physical database.

Primary classes are SQLiteCursor, SQLiteDatabase, SQLiteQuery,

SQLiteQueryBuilder, and SQLiteStatement. However, most of your

interaction is going to be with classes from the abstract

android.database package.

android.drm: Classes related to Digital Rights Management.

android.gesture: Houses all the classes and interfaces necessary to

work with user-defined gestures. Primary classes are Gesture,

GestureLibrary, GestureOverlayView, GestureStore, GestureStroke,

and GesturePoint. A Gesture is a collection of GestureStrokes and

GesturePoints. Gestures are collected in a GestureLibrary. Gesture

libraries are stored in a GestureStore. Gestures are named so that they

can be identified as actions. Some of the classes from this package

are covered in Chapter 27.

android.graphics: Contains the classes Bitmap, Canvas, Camera, Color,

Matrix, Movie, Paint, Path, Rasterizer, Shader, SweepGradient, and

TypeFace.

android.graphics.drawable: Implements drawing protocols and

background images, and allows animation of drawable objects.

android.graphics.drawable.shapes: Implements shapes including

ArcShape, OvalShape, PathShape, RectShape, and RoundRectShape.

android.hardware: Implements the physical Camera-related classes.

The Camera represents the hardware camera, whereas

android.graphics.Camera represents a graphical concept that’s not

to a physical camera at all.

android.hardware.usb: Lets you talk to USB devices from Android.

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