1. Introduction to Android

The Android portion of this book is geared toward people who know Java object-oriented programming. If you do not know Java or another object-oriented programming language, the appendices provide a friendly introduction to Java and the object-oriented programming techniques you’ll need to develop Android apps. We use only complete working Android apps, so if you have object-oriented programming experience in another language, such as C#, Objective-C/Cocoa or C++ (with class libraries), you should be able to master the material quickly, learning a good amount of Java and Java-style object-oriented programming as you learn Android app development.

• The first-generation Android phones were released in October 2008. As of June 2015, Android had 82.8% of the global smartphone market share, compared to 13.9% for Apple and 2.6% for Microsoft.¹

1. http://www.idc.com/prodserv/smartphone-os-market-share.jsp.

• Billions of apps have been downloaded from Google Play and more than one billion Android devices were shipped worldwide in 2014.²

2. http://www.cnet.com/news/android-shipments-exceed-1-billion-for-first-time-in-2014/.

• According to PC World, approximately 230 million tablets shipped in 2014 of which 67.3% were Android tablets, compared to 27.6% for iOS and 5.1% for Microsoft Windows.³

3. http://www.pcworld.com/article/2896196/windows-forecast-to-gradually-grab-tablet-market-share-from-ios-and-android.html.

• Android devices now include smartphones, tablets, e-readers, robots, jet engines, NASA satellites, game consoles, refrigerators, televisions, cameras, health-care devices, smartwatches, automobile in-vehicle “infotainment” systems (for controlling the radio, GPS, phone calls, thermostat, etc.) and more.⁴

4. http://www.businessweek.com/articles/2013-05-29/behind-the-internet-of-things-isandroid-and-its-everywhere.

• A recent report says that mobile app revenue (across all mobile platforms) is expected to reach reach $99 billion by 2019.⁵

5. http://www.telecompetitor.com/mobile-app-forecast-calls-for-revenue-of-99-billion-by-2019/.

or by participating in the Open Source Project discussion groups

Numerous open-source Android apps from Google and others are available on the Internet (Fig. 1.1). Figure 1.2 shows you where you can get the Android source code, learn about the philosophy behind the open-source operating system and get licensing information.

The openness of the platform spurs rapid innovation. Unlike Apple’s proprietary iOS, which is available only on Apple devices, Android is available on devices from dozens of original equipment manufacturers (OEMs) and through numerous telecommunications carriers worldwide. The intense competition among OEMs and carriers benefits customers.

Java is object oriented and has access to extensive class libraries that help you quickly develop powerful apps. GUI programming in Java is event driven—in this book, you’ll write apps that respond to various user-initiated events such as screen touches. In addition to directly programming portions of your apps, you’ll also use the Android Studio IDE to conveniently drag and drop predefined objects such as buttons and textboxes into place on your screen, and label and resize them. Using Android Studio, you can create, run, test and debug Android apps quickly and conveniently.

combines the photos and tweets from Twitter with the mapping capabilities of Google Maps to allow you to explore countries around the world through the photos of others.

Programmableweb

provides a directory of over 14,000 APIs and mashups, plus how-to guides and sample code for creating your own mashups. Figure 1.4 lists some popular web services. We use OpenWeatherMap.org’s weather web services in Chapter 7.

was formed to develop, maintain and evolve Android, driving innovation in mobile technology and improving the user experience while reducing costs.

In this section, we walk through the evolution of the Android operating system, showing its versions and their key functionality. The Android marketplace is fragmented—many devices still use older Android versions—so it’s helpful for you to be aware of the features introduced in each version.

6. http://code.google.com/android/c2dm/.

For information about additional Android 2.2 features—OpenGL ES 2.0 graphics capabilities, the media framework and more—visit

One of the most significant new features in Android 2.3 was support for near-field communication (NFC)—a short-range wireless connectivity standard that enables communication between two devices within a few centimeters. NFC support and features vary by Android device. NFC can be used for payments (for example, touching your NFC-enabled Android device to a payment device on a soda machine), exchanging data such as contacts and pictures, pairing devices and accessories and more. For more Android 2.3 developer features, see

• fragments, which describe portions of an app’s user interface and can be combined into one screen or used across multiple screens

• a persistent Action Bar at the top of the screen providing users with options for interacting with apps

• the ability to add large-screen layouts to existing apps designed for small screens to optimize your app for use on different screen sizes

• a visually attractive and more functional user interface, known as “Holo” for its holographic look and feel

• a new animation framework

• improved graphics and multimedia capabilities

• ability to use multicore processor architectures for enhanced performance

• increased Bluetooth support (e.g., enabling an app to determine if there are any connected devices such as headphones or a keyboard)

• and an animation framework for animating user-interface or graphics objects.

For a list of Android 3.0 user and developer features and platform technologies, go to

• Google Cloud Messaging—a cross-platform solution that enables developers to deliver messages to devices

• Google Play Services—a set of APIs for incorporating Google functionality into your apps.

For the Jelly Bean features list, see

7. http://techcrunch.com/2013/10/31/android-4-4-kitkat-google/.

Enabling more users to update to KitKat reduced the “fragmentation” of Android versions in the market, which has been a challenge for developers who previously had to design apps to run across multiple versions of the operating system, or limit their potential market by targeting their apps to a specific version of the operating system.

Android KitKat also includes security and accessibility enhancements, improved graphics and multimedia capabilities, memory-use analysis tools and more. Figure 1.8 lists some of the key KitKat features. For a complete list, see

8. http://www.statista.com/statistics/266210/number-of-available-applications-inthe-google-play-store/.

then specify the Android device on which to install the app. It will then download via the device’s Wi-Fi or 3G/4G connection. In Chapter 10, Google Play and App Business Issues, we discuss additional app stores, offering your apps for free or charging a fee, app pricing and more.

Figure 1.12 lists many of the packages we discuss in this book. For a complete list of Android packages, see

Several of the packages we use are from the Android Support libraries, which enable you to use newer Android features in apps that run on current and older platforms. For an overview of the key features in the Android Support libraries, visit:

9. Android Studio is based on the JetBrains IntelliJ IDEA Java IDE (http://www.jetbrains.com/idea/).

• GUI designer

• code editor with support for syntax coloring and line numbering

• auto-indenting and auto-complete (i.e., type hinting)

• debugger

• version control system

• refactoring support

and more.

Before running an app in the emulator, you’ll need to create an Android Virtual Device (AVD), which defines the characteristics of the device on which you want to test, including the hardware, system image, screen size, data storage and more. If you want to test your apps for multiple Android devices, you’ll need to create separate AVDs to emulate each unique device, or use Google’s Cloud Test Lab

which enables you to test on many different devices.

You can reproduce on the emulator most of the Android gestures (Fig. 1.13) and controls (Fig. 1.14) using your computer’s keyboard and mouse. The gestures on the emulator are a bit limited, since your computer probably cannot simulate all the Android hardware features. For example, to test GPS apps in the emulator, you’ll need to create files that simulate GPS readings. Also, although you can simulate orientation changes (to portrait or landscape mode), simulating particular accelerometer readings (the accelerometer allows the device to respond to up/down, left/right and forward/backward acceleration) requires features that are not built into the emulator. The emulator can, however, use sensor data from an actual Android device connected to the computer, as described at

Figure 1.15 lists Android functionality that’s not available on the emulator. You can install your app on an Android device to test these features. You’ll start creating AVDs and using the emulator to develop Android apps in Chapter 2’s Welcome app.

Building software quickly, correctly and economically remains an elusive goal at a time when demands for new and more powerful software are soaring. Objects, or more precisely—as we’ll see in Chapter 3—the classes objects come from, are essentially reusable software components. There are date objects, time objects, audio objects, video objects, automobile objects, people objects, etc. Almost any noun can be reasonably represented as a software object in terms of attributes (e.g., name, color and size) and behaviors (e.g., calculating, moving and communicating). Software developers are discovering that using a modular, object-oriented design-and-implementation approach can make software development groups much more productive than they could be with earlier popular techniques like “structured programming”—object-oriented programs are often easier to understand, correct and modify.

Just as you cannot cook meals in the kitchen of a blueprint, you cannot drive a car’s engineering drawings. Before you can drive a car, it must be built from the engineering drawings that describe it. A completed car has an actual accelerator pedal to make it go faster, but even that’s not enough—the car won’t accelerate on its own (hopefully!), so the driver must press the pedal to accelerate the car.

An object, similarly, has attributes that it carries along as it’s used in a program. These attributes are specified as part of the object’s class. For example, a bank-account object has a balance attribute that represents the amount of money in the account. Each bank-account object knows the balance in the account it represents, but not the balances of the other accounts in the bank. Attributes are specified by the class’s instance variables.

To create the best solutions, you should follow a detailed analysis process for determining your project’s requirements (i.e., defining what the system is supposed to do) and developing a design that satisfies them (i.e., deciding how the system should do it). Ideally, you’d go through this process and carefully review the design (and have your design reviewed by other software professionals) before writing any code. If this process involves analyzing and designing your system from an object-oriented point of view, it’s called an object-oriented analysis and design (OOAD) process. Languages like Java are object oriented. Programming in such a language, called object-oriented programming (OOP), allows you to implement an object-oriented design as a working system.

1. Checking your setup. If you have not done so already, perform the steps specified in the Before You Begin section.

2. Opening Android Studio. Use the Android Studio shortcut

to open the IDE. On Windows, the shortcut will appear in your Start menu or Start screen. On OS X, the shortcut is located in your Applications folder. On Linux, the shortcut’s location depends on where you extract the ZIP file containing the Android Studio files. Once you open Android Studio for the first time, the Welcome to Android Studio window appears (Fig. 1.17).

3. Opening the Tip Calculator app’s project. In Android Studio, when another project is already open, you can select File > Open... to navigate to that project's location and open it, or in the Welcome to Android Studio Window (Fig. 1.17), you can click Open an existing Android Studio Project to open the Open File or Project dialog (Fig. 1.18). Navigate to the book’s examples folder, select the TipCalculator folder and click Choose (Mac) or OK (Windows/Linux). Android Studio stores the Android SDK’s path in the project settings for each project you create. When you open our projects on your system, you’ll receive an error message if the SDK on your system is in a different location from ours. Simply click the OK button in the error dialog that appears, and Android Studio will update the project settings to use the SDK on your system. At this point, the IDE opens the project and displays its contents in the Project window (Fig. 1.19) at the IDE’s left side. If the Project window is not visible, you can view it by selecting View > Tool Windows > Project.

10. At the time of this writing, when you set up Android Studio, it configures an AVD that emulates a Google Nexus 5 phone running Android 6.0 (Marshmallow). You’ll still need to perform Section 1.9.2’s steps to create the additional AVDs you need for testing.

1. In Android Studio, select Tools > Android > AVD Manager to display the Android Virtual Device Manager window (Fig. 1.20).

2. Click Create Virtual Device... to open the Virtual Device Configuration window (Fig. 1.21). By default the Category “Phone” is selected, but you may also create AVDs for Tablet, Wear and TV. For your convenience, Google provides many preconfigured devices that you can use to quickly create AVDs. Select Nexus 6, then click Next.

3. Select the system image for the virtual device you wish to create—in this case, the one with the Android platform Release Name value Marshmallow, the API Level value 23, the ABI (application binary interface) value x86 and the Target value Android 6.0 (with Google APIs), then click Next. This Target creates an Android AVD for Android 6 that also includes support for Google Play Services APIs.

4. For the AVD Name, specify Nexus 6 API 23.

5. Click the Show Advanced Settings button in the lower-left of the Virtual Device Configuration window, then scroll to the bottom of the advanced settings and uncheck the Enable Keyboard Input option and click Finish to create the AVD.

6. Repeat Steps 1–6 to create a Nexus 9 tablet AVD named Nexus 9 API 23—you’ll use this tablet AVD in Chapter 2.

If you leave the Enable Keyboard Input option checked in Step 5 above, you can use your computer’s keyboard to enter data into apps running in the AVD. However, this prevents the soft keyboard shown in the screen captures from displaying.

Each AVD you create has many other options specified in its config.ini file. To more precisely match a particular device’s hardware configuration, you can modify config.ini as described at:

1. Checking your setup. If you have not done so already, perform the steps specified in the Before You Begin section.

2. Launching the Nexus 6 AVD. For this test-drive, we’ll use the Nexus 6 smartphone AVD that you configured in Section 1.9.2. To launch the Nexus 6 AVD, select Tools > Android > AVD Manager to display the Android Virtual Device Manager dialog (Fig. 1.22). Click the Launch this AVD in the emulator button () in the row for the Nexus 6 API 23 AVD. An AVD can take some time to load—do not attempt to execute the app until the AVD finishes loading. When it’s done loading, the AVD will display the lock screen. On an actual device, you unlock it by swiping up with your finger. You perform the swipe gesture on an AVD by placing the mouse over the AVD’s “screen” and dragging up with the mouse. Figure 1.23 shows the AVD after you unlock it.

3. Launching the Tip Calculator app. In Android Studio, select Run > Run 'app' or click the Run 'app' button () on the Android Studio toolbar. This will display a Device Chooser dialog (Fig. 1.24) with the currently running AVD already selected. Click OK to run the Tip Calculator in the AVD (Fig. 1.25) that you launched in Step 2.¹¹ As an alternative to opening the Android Virtual Device Manager dialog in Step 2, you can click the Run 'app' button () on the Android Studio toolbar and the Device Chooser dialog will appear. You can then use the Launch emulator option at the bottom of the dialog to select an AVD to launch, and in which to run the app.

11. The keypad in Fig. 1.25 may differ, based on your AVD’s or device’s Android version or whether you’ve installed and selected a custom keyboard. We configured our AVD to display the dark keyboard for better contrast in our screen captures. To do so: Touch the home () icon on your AVD or device. On the home screen, touch the launcher () icon, then open the Settings app. In the Personal section, touch Language and Input. On an AVD, touch Android Keyboard (AOSP). On a device, touch Google Keyboard (the standard Android keyboard). Touch Appearance & layouts, then touch Theme. Touch Material Dark to change to the keyboard with the dark background.

4. Exploring the AVD. At the AVD screen’s bottom are various soft buttons that appear on the device’s touch screen. You touch these to interact with apps and the Android OS. In an AVD touches are performed by clicking with the mouse. The down button () dismisses the keypad. When there is no keypad on the screen the back button () appears instead. Touching this button takes you back to an app’s prior screen, or back to a prior app if you’re in the current app’s initial screen. The home button () returns you to the device’s home screen. The recent apps button () allows you to view the recently used apps list, so that you can switch back to recent apps quickly. At the screen’s top is the app’s app bar, which displays the app’s name and may contain other app-specific soft buttons—some may appear on the app bar and the rest in the app’s options menu, which appears in the app bar at the top of the screen as . The number of options on the app bar depends on the size of the device—we discuss this in Chapter 5.

5. Entering a Bill Total. Enter the bill total 56.32 by touching numbers on the numeric keypad. If you make a mistake, press the delete button () in the bottom-right corner of the keypad to erase the last digit you entered. Even though the keypad contains a decimal point, the app is configured so that you may enter only the digits 0–9. Each time you touch a digit or delete one, the app reads what you’ve entered so far and converts it to a number—if you delete all the digits the app redisplays Enter Amount in the TextView at the top of the app. The app divides the value by 100 and displays the result in the blue TextView. The app then calculates and updates the tip and total amounts that are displayed. We use Android’s locale-specific currency-formatting capabilities to display monetary values formatted for the device’s current locale. For the U.S. locale, as you enter the four digits 5, 6, 3 and 2, the bill total is displayed successively as $0.05, $0.56, $5.63 and $56.32, respectively.

6. Selecting a Custom Tip Percentage. The SeekBar allows you to select a custom percentage, and the TextViews in the right column below the SeekBar display the corresponding tip and the total bill. Drag the SeekBar thumb to the right until the custom percentage reads 25%. As you drag the thumb, the SeekBar value continuously changes. The app updates the tip percentage, the tip amount and the bill total accordingly for each SeekBar value until you release the thumb. Figure 1.26 shows the app after you’ve entered the bill amount and selected the tip percentage.

7. Returning to the home screen. You can return to the AVD’s home screen by tapping the home () button on the AVD.

1. In Android Studio, select Tools > Android > AVD Manager to open the Android Virtual Device Manager window.

2. You’ll see a list of existing AVDs. For the AVD you’d like to reconfigure, click the pencil icon () in the Actions column.

3. In the Virtual Device Configuration window, click Show Advanced Settings, and scroll to the Memory and Storage section.

4. Decrease value for RAM from the default 1536 MB (1.5 GB) down to 1 GB.

5. Click Finish and close the Android Virtual Device Manager window.

If you still cannot run the AVD, repeat these steps and reduce the memory to 768 MB.

1. Enabling the developer options on the device. First, you must enable debugging on the device. To do so, go to the device’s Settings app, then select About phone (or About tablet), locate the Build number (at the bottom of the list) and tap it seven times until you see You are now a developer on the screen. This will enable an entry named Developer options in the Settings app.

2. Enabling debugging on the device. Return to the Settings app’s main screen, select Developer options and ensure that USB debugging is checked—this is the default when you first enable the developer options on the device.

3. Connecting your device. Next, use the USB cable that came with your device to connect the device to your computer. If you’re a Windows user, recall from the Before You Begin section that you might need to install a USB driver for your device. See the following web pages for details:

4. Running Tip Calculator on the Android device. In Android Studio, select Run > Run 'app' or click the Run 'app' button () on the Android Studio toolbar. This will display the Device Chooser dialog that you saw in Fig. 1.24. Select your device from the list of running AVDs and devices. Click OK to run the Tip Calculator on the AVD or device you selected.

This file contains options that are not configurable via the Android Virtual Device Manager. Modifying these options allows you to more precisely match the hardware configuration of an actual device.

12. http://www.statista.com/statistics/266210/number-of-available-applications-inthe-google-play-store/.

In Chapter 2, you’ll build your first Android app in Android Studio. The app will display text and an image. You’ll also learn about Android accessibility and internationalization.

a) In 2007, the __________ was formed to develop, maintain and evolve Android, driving innovation in mobile technology and improving the user experience while reducing costs.

b) The __________ IDE allows you to create, run and debug Android apps.

c) Multitouch screens allow you to control your Android device with __________ involving one touch or multiple simultaneous touches.

d) With web services, you can create __________, which enable you to rapidly develop apps by quickly combining complementary web services, often from different organizations and possibly other forms of information feeds.

e) Android uses a collection of __________, which are named groups of related, predefined classes.

f) The __________, included in the Android SDK, allows you to run Android apps in a simulated environment within Windows, Mac OS X or Linux.

g) Almost any noun can be reasonably represented as a software object in terms of __________ (e.g., name, color and size) and behaviors (e.g., calculating, moving and communicating).

h) A program unit called a(n) __________ houses the methods that perform its tasks.

i) You send messages to an object. Each message is a(n) __________ that tells a method of the object to perform its task.

1.2 State whether each of the following is true or false. If false, explain why.

a) One benefit of developing Android apps is that the operating system is proprietary to Google.

b) The openness of the Android platform discourages innovation.

c) You can reuse a class many times to build many objects. Reuse of existing classes when building new classes and programs saves time and effort.

d) Attributes are specified by the class’s methods.

e) Objects may communicate with one another, but they’re normally not allowed to know how other objects are implemented—implementation details are hidden within the objects themselves.

1.3 Fill in the blanks in each of the following statements (based on Section 1.8):

a) Objects have the property of __________—although objects communicate with one another, they’re normally not allowed to know how other objects are implemented.

b) The __________ that objects come from are essentially reusable software components; they include attributes and behaviors.

c) The process of analyzing and designing a system from an object-oriented point of view is called __________.

d) With __________, new classes of objects are derived by absorbing characteristics of existing classes, then adding unique characteristics of their own.

e) The size, shape, color and weight of an object are considered __________ of the object’s class.

f) A class that represents a bank account might contain one __________ to deposit money to an account, another to withdraw money from an account and a third to inquire what the account’s current balance is.

g) You must build an object of a class before a program can perform the tasks that the class’s methods define—this process is called __________.

h) The balance of a bank account class is an example of a(n) __________ of that class.

i) Your project’s requirements define what the system is supposed to do and your design specifies __________ the system should do it.

a) Open Handset Alliance.

b) Android Development Tools (ADT).

c) gestures.

d) mashups.

e) packages.

f) Android emulator.

g) attributes.

h) class.

i) method call.

1.2

a) False. The operating system is open source and free.

b) False. The openness of the platform spurs rapid innovation.

c) True.

d) False. Attributes are specified by the class’s instance variables.

e) True.

1.3

a) information hiding.

b) classes.

c) object-oriented analysis and design (OOAD).

d) inheritance.

e) attributes.

f) method.

g) instantiation.

h) attribute.

i) how.

a) Android apps are developed with __________—one of the world’s most widely used programming language, a logical choice because it’s powerful, free and open source.

b) GUI programming in Java is __________ driven, so you’ll write apps that respond to various user interactions such as screen touches and keystrokes.

c) Touching the screen and holding your finger in position is called a(n) __________.

d) Touching the screen, then moving your finger in one direction and releasing it is called a(n) __________.

e) Before running an app in the emulator, you'll need to create a(n) __________, which defines the characteristics of the device on which you want to test, including the hardware, system image, screen size, data storage and more.

f) Performing a task in a program requires a(n) __________ which houses the program statements that actually perform its tasks.

g) You must build an object of a class before a program can perform the tasks that the class’s methods define. The process of doing this is called __________.

h) __________ helps you build more reliable and effective systems, because existing classes and components often have gone through extensive testing, debugging and performance tuning.

i) Classes __________ (i.e., wrap) attributes and methods into objects—an object’s attributes and methods are intimately related.

j) A new class of objects can be created quickly and conveniently by __________—the new class absorbs the characteristics of an existing one, possibly customizing them and adding unique characteristics of its own.

k) Unlike actual buttons on a device, __________ buttons appear on the device’s touch screen.

l) __________ was the complete user-interface redesign that Google introduced with Android 5.0.

m) Among its many new features, Android 6.0 introduced a new __________ to make apps easier to install.

1.5 State whether each of the following is true or false. If false, explain why.

a) The vast majority of Android development is done in C++.

b) You can reproduce on the emulator most of the Android gestures and controls using your computer’s keyboard and mouse.

c) Objects, or more precisely the classes objects come from, are essentially reusable software components.

1.6 One of the most common objects is a wrist watch. Discuss how each of the following terms and concepts applies to the notion of a watch: object, attributes, behaviors, class, inheritance (consider, for example, an alarm clock), messages, encapsulation and information hiding.