COMPANION eBOOK US $44.99 Shelve in Mobile Computing User level: Intermediate www.apress.com BOOKS FOR PROFESSIONALS BY PROFESSIONALS ® A ndroid Recipes teaches you how to develop top-notch apps using a proven problem-solution approach. First, a problem is identified. Then a clear expla- nation of the solution is given, supported by a fully worked code sample. Best of all, you can apply all the code examples found in the book directly to your own projects—saving you time and a great deal of work! This new edition offers more than 100 down-to-earth recipes that will teach you how to: • Use external libraries to save time and effort • Boost app performance by using the Android NDK and Renderscript • Design apps for performance, responsiveness, and seamlessness • Send data between devices and other external hardware • Persist application data and share it between applications • Capture and play back various device media items • Communicate with web services • Get the most out of your user interface • Develop a unit conversion app in the context of the command-line/ Android SDK and Eclipse/Android SDK environments Crammed with insightful instruction and helpful examples, this second edi- tion of Android Recipes is your guide to writing apps for one of today’s hottest mobile platforms. It offers pragmatic advice that will help you get the job done quickly and well. Dave Smith | Jeff Friesen A valuable coding reference for creating all kinds of Android apps Companion eBook Available Smith Friesen Android Recipes SOURCE CODE ONLINE SECOND EDITION SECOND EDITION Android Recipes A Problem-Solution Approach www.it-ebooks.info 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. www.it-ebooks.info iii Contents at a Glance  Foreword xviii  About the Authors xix  About the Technical Reviewer xx  Acknowledgments xxi  Preface xxii  Chapter 1: Getting Started with Android 1  Chapter 2: User Interface Recipes 99  Chapter 3: Communications and Networking 323  Chapter 4: Interacting with Device Hardware and Media 421  Chapter 5: Persisting Data 501  Chapter 6: Interacting with the System 581  Chapter 7: Working with Libraries 689  Chapter 8: Working with Android NDK and Renderscript 743  Appendix A: Scripting Layer for Android 805  Appendix B: Android Tools Overview 821  Appendix C: App Design Guidelines 855  Appendix D: Univerter Architecture 867  Index 911 www.it-ebooks.info 1 1 Chapter Getting Started with Android Android is hot, and many people are developing Android applications (apps for short). Perhaps you too would 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/index.html) to acquire the needed knowledge, you might be overwhelmed by the guide’s vast amount of information. In contrast, this chapter presents just enough theory to help you grasp the basics. Following this theory are recipes that teach you how to develop apps and prepare them for publication on Google Play (https://play.google.com/store). What Is Android? The Android Developer’s Guide formerly defined Android as a software stack a s e t o f s oft wa re s u bs ys te ms n e ed e d to d e li ve r a f u ll y f unc ti on a l s ol ut io n 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:  Application framework enabling reuse and replacement of app components (discussed later in this chapter) www.it-ebooks.info CHAPTER 1: Getting Started with Android 2  Bluetooth, EDGE, 3G, and WiFi support (hardware dependent)  Camera, GPS, compass, and accelerometer support (hardware dependent)  Dalvik virtual machine optimized for mobile devices  GSM Telephony support (hardware dependent)  Integrated browser based on the open source WebKit engine  Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)  Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0, 1.1, or 2.0 specification (hardware acceleration optional)  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 plug-in for the Eclipse integrated development environment [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 the summer of 2005 and released a beta version of the Android SDK in November 2007. On September 23, 2008, Google released Android 1.0, whose core features included a web browser, camera support, Google Search, and more. Table 1-1 outlines subsequent 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 Releases Version Release Date and Changes 1.1 Google released SDK 1.1 on February 9, 2009. Changes included showing/hiding the speakerphone dialpad and saving attachments in messages. 1.5 (Cupcake) Based on Linux Kernel 2.6.27 Google released SDK 1.5 on April 30, 2009. Changes included recording and watching videos in MPEG-4 and 3GP formats, populating the home screen (a special app that is a starting point for using an www.it-ebooks.info CHAPTER 1: Getting Started with Android 3 Android device) with widgets (miniature app views), and animated screen transitions. 1.6 (Donut) Based on Linux Kernel 2.6.29 Google released SDK 1.6 on September 15, 2009. Changes included an expanded Gesture framework and the new GestureBuilder development tool, an integrated camera/camcorder/gallery interface, support for WVGA screen resolutions, and an updated search experience. 2.0/2.1 (Éclair) Based on Linux Kernel 2.6.29 Google released SDK 2.0 on October 26, 2009. Changes included live wallpapers, numerous new camera features (including flash support, digital zoom, scene mode, white balance, color effect, and macro focus), improved typing speed on virtual keyboard, a smarter dictionary that learns from word usage and includes contact names as suggestions, improved Google Maps 3.1.2, 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. Version 2.0.1 focused on minor API changes, bug fixes, and framework behavioral changes. Version 2.1 presented minor amendments to the API and bug fixes. 2.2 (Froyo) Based on Linux Kernel 2.6.32 Google released SDK 2.2 on May 20, 2009. Changes included the integration of Chrome’s V8 JavaScript engine into the Browser app, voice dialing and contact sharing over Bluetooth, Adobe Flash support, additional app speed improvements through JIT compilation, and USB tethering and WiFi hotspot functionality. Google subsequently released SDK update 2.2.1 on January 18, 2011, to offer bug fixes, security updates, and performance improvements. It then released SDK update 2.2.2 on January 22, 2011, to provide minor bug fixes, including SMS routing issues that affected the Nexus One. Finally, Google released SDK update 2.2.3 on November 21, 2011, and this contained two security patches. 2.3 (Gingerbread) Based on Linux Kernel 2.6.35 Google released SDK 2.3 on December 6, 2010. Changes included a new concurrent garbage collector that improves an app’s responsiveness, support for gyroscope and barometer sensing, support for WebM/VP8 video playback and AAC audio encoding, support for near field communication, and enhanced copy/paste functionality that lets users select a word by press-hold, copy, and paste. Google subsequently released SDK update 2.3.3 on February 9, 2011, offering improvements and API fixes. SDK update 2.3.4 on April 28, 2011, added support for voice or video chat via Google Talk. SDK update 2.3.5 on July 25, 2011, offered system enhancements, shadow animations for list scrolling, improved battery efficiency, and more. SDK update 2.3.6 on September 2, 2011, fixed a voice search bug. SDK update 2.3.7 on September 21, 2011, brought support for Google Wallet to the Nexus S 4G. www.it-ebooks.info CHAPTER 1: Getting Started with Android 4 3.0 (Honeycomb) Based on Linux 2.6.36 Google released SDK 3.0 on February 22, 2011. Unlike previous releases, version 3.0 focuses exclusively on tablets, such as Motorola Xoom, the first 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. Google subsequently released SDK updates 3.1, 3.2, 3.2.1, 3.2.2, 3.2.4, and 3.2.6 throughout 2011 and in February 2012. 4.0 (Ice Cream Sandwich) Based on Linux Kernel 3.0.1 Google released SDK 4.0.1 on October 19, 2011. SDK 4.0.1 and 4.x successors unify the 2.3.x smartphone and 3.x tablet SDKs. Features include 1080p video recording and a customizable launcher. Google subsequently released SDK updates 4.0.2, 4.0.3, and 4.0.4 in late 2011 and in March 2012. 4.1 (Jelly Bean) Google released SDK 4.1 on June 27, 2012. Features include vsync timing, triple buffering, automatically resizable app widgets, improved voice search, multichannel audio, and expandable notifications. An over-the-air update (version 4.1.1) was released later in July. In early October, Google released SDK 4.1.2, which offers lock/home screen rotation support for the Nexus 7, one-finger gestures to expand/collapse notifications, and bug fixes/performance enhancements. Then, in late October, Google released SDK 4.2, which offers Photo Sphere panorama photos, multiple user accounts (tablets only), a “Daydream” screensaver that activates when the device is idle or docked, notification power controls, support for a wireless display (Miracast), and more. 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. www.it-ebooks.info CHAPTER 1: Getting Started with Android 5 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. NOTE: Apps are written in a nonstandard Java implementation that combines Android-specific APIs with Java 5 APIs and a small amount of Java 6 (such as the java.io.File class’s boolean setExecutable(boolean executable, boolean ownerOnly) method). Because Android does not support most Java 6 and all Java 7 APIs, you cannot leverage newer Java APIs and dependent features. For example, you cannot use Java 7’s try-with-resources statement, which depends upon Java 7’s java.lang.AutoCloseable interface. www.it-ebooks.info CHAPTER 1: Getting Started with Android 6 Each Android version (including updates) is assigned an API level, an integer value uniquely identifying the framework API revision offered by that version of the Android platform. For example, Android 4.1 is assigned API Level 16 and Android 2.3.4 is assigned API Level 10. APIs with higher API levels typically cannot be used on devices with lower API levels. (Google’s support library, which is discussed in Chapter 7, makes certain newer APIs available to older platform versions.) For example, you typically cannot use an API at Level 16 on a device that supports only API Level 10 (and lower). API-level constants are available in the android.os.Build.VERSION_CODES class. Consult “Android API Levels” (http://developer.android.com/guide/topics/manifest/uses-sdk- element.html#ApiLevels) in the Android Developer’s Guide to learn more about API levels. 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:  Activity Manager : This component provides an app’s life cycle and maintains a shared activity stack for navigating within and among apps. Both topics are discussed later in this chapter.  Content Providers : These components encapsulate data (such as the Browser app’s bookmarks) that can be shared among apps.  Location Manager : This component makes it possible for an Android device to be aware of its physical location.  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.  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.)  Resource Manager : This component lets an app access its resources, a topic that’s discussed later in this chapter.  Telephony Manager : This component lets an app learn about a device’s telephony services. It also handles making and receiving phone calls. www.it-ebooks.info CHAPTER 1: Getting Started with Android 7  View System : This component manages user interface elements and user interface-oriented event generation. (These topics are briefly discussed later in this chapter.)  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 functions. Developers interact with the following libraries by way of framework APIs:  FreeType : This library supports bitmap and vector font rendering.  libc : This library is a BSD-derived implementation of the standard C system library, tuned for embedded Linux-based devices.  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.  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.  OpenGL | ES : These 3D graphics libraries provide an OpenGL implementation based on OpenGL ES 1.0/1.1/2.0 APIs. They use hardware 3D acceleration (where available) or the included (and highly optimized) 3D software rasterizer.  SGL : This library provides the underlying 2D graphics engine.  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.  SSL : This library provides secure sockets layer‒based security for network communication. www.it-ebooks.info [...]... implicit intents Android consults an Intent object’s action, category, data, and type when comparing the intent against an intent filter It doesn’t take extras and flags into consideration www.it-ebooks.info 11 12 CHAPTER 1: Getting Started with Android NOTE: Android widely uses intents, which offers many opportunities to replace existing components with your own components For example, Android provides... designated class If not set, Android uses other information in the Intent object to locate a suitable target  Data: The uniform resource identifier of the data on which to operate (such as a person record in a contacts database) www.it-ebooks.info CHAPTER 1: Getting Started with Android  Extras: A set of key-value pairs providing additional  Flags: Bit values that instruct Android on how to launch an... 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 www.it-ebooks.info CHAPTER 1: Getting Started with Android. .. with which the user interacts For example, Android s Contacts app includes an activity for entering a new contact, its Phone app includes an activity for dialing a phone number, and its Calculator app includes an activity for performing basic calculations (see Figure 1-2) www.it-ebooks.info CHAPTER 1: Getting Started with Android Figure 1-2 The main activity of Android s Calculator app lets the user perform... override various Activity life cycle callback methods that Android calls during the life of an activity For example, the SimpleActivity class in Listing 1-1 extends Activity and also overrides the void onCreate(Bundle bundle) and void onDestroy() life cycle callback methods Listing 1-1 A Skeletal Activity import android. app.Activity; import android. os.Bundle; public class SimpleActivity extends Activity... passed an android. os.Bundle object containing the activity’s previous state, if that state was captured (via void onSaveInstanceState(Bundle outState)); otherwise, the null reference is passed Android always calls the onStart() method after calling onCreate(Bundle) All meaningful activities override onCreate(Bundle)  onStart() is called just before the activity becomes visible to the user Android calls... started again Android always calls onStart() after calling onRestart()  onResume() is called just before the activity starts interacting with the user At this point the activity has the focus and user input is directed to the activity Android always calls the onPause() method after calling onResume(), but only when the activity must be paused www.it-ebooks.info CHAPTER 1: Getting Started with Android ... view groups) NOTE: Android refers to views as widgets Don’t confuse widget in this context with the widgets that are shown on the Android home screen Although the same term is used, user interface widgets and home screen widgets are different User interface widgets are components; home screen widgets are miniature views of running apps Views are described by subclasses of the concrete android. view.View... android. view.View class and are analogous to Java Swing components The android. widget package contains various View subclasses, such as Button, EditText, and TextView (the parent of EditText) View groups are described by subclasses of the abstract android. view.ViewGroup class (which subclasses View) and are analogous to Java Swing containers The android. widget package contains various subclasses, such as LinearLayout... activity that initiated the music leaves the screen Services are described by subclasses of the abstract android. app.Service class, which is an indirect subclass of Context www.it-ebooks.info CHAPTER 1: Getting Started with Android Service subclasses override various Service life cycle callback methods that Android calls during the life of a service For example, the SimpleService class in Listing 1-2 extends . creating all kinds of Android apps Companion eBook Available Smith Friesen Android Recipes SOURCE CODE ONLINE SECOND EDITION SECOND EDITION Android Recipes A Problem-Solution. command-line/ Android SDK and Eclipse /Android SDK environments Crammed with insightful instruction and helpful examples, this second edi- tion of Android Recipes