CHAPTER 1
Introduction
Chapter objectives
• Understand what Android is
• Learn the differences between Java and
Android Java
• Examine the Android project structure
• Build a basic application using Android Studio
• Learn about the Model-View-Controller design
1.1 Android Platforms
• First-generation Android phones did not include
many of the features users are familiar with
• Since 2008, Android has been enhanced in a
multitude of ways, improving its performance,
the user interface design, and adding many
features, such as voice searching
• By 2015, Android applications were including
fluid animations, bold color palettes, and
sophisticated multitasking menus that featured
voice interactions
Table 1-1 shows the evolution of
Android
• Google services were integrated as part of
the Android operating system since the first
installment
• Two of the most substantial inclusions of
Android 1.0 were Google Maps and
Notifications
• Notifications remains an important part of
the Android user interface
• In current releases of Android, this feature
has been refined to include chat messages
and calendar events that support
synchronization across all Android devices
• By the time Cupcake appeared in 2009,
refinements, such as the inclusion of selfrefreshing widgets and copy-and-paste,
had been implemented
• One of the most significant features that
emerged with Cupcake was the
introduction of a soft keyboard, which also
brought the first forms of keyboard skins
• Keyboard skins are created by third-party
developers to provide enhancements to an
existing soft keyboard
• Unique to Android, skins allow users to
personalize their keyboard
• Skins have evolved alongside Android and
have shifted beyond basic appearance and
into more extensive behavior than
originally seen in Cupcake
• Today, Android device manufacturers
regularly offer skins that enhance the user
experience by adding functionality to the
design.
• Android 2.2 was created with the ability to
execute far faster than previous versions
• This was due to the introduction of the new
Dalvik Just-In-Time (JIT) compiler, first seen on
Froyo
• Dalvik allowed for better CPU performance,
which significantly enhanced processing
power
• Froyo’s browser came with a new JavaScript
engine, making Internet browsing nearly three
times faster than the previously released
version of Android
• Froyo also brought native support for
tethering.
• Gingerbread the first version of Android
that backed multi-core processing on
mobile devices
• For application developers, Gingerbread
brought support for new technologies,
such as NFC (Near Field Communication),
and SIP (Session Initiation Protocol)
• The SIP API provides developers with
tools to create applications that perform
video conferencing and instant
messaging
• Honeycomb was released as the first
version of Android specifically
implemented for tablets
• Prior to Honeycomb, Android tablets were
running on phone operating systems that
were stretched to fit the screen of a larger
tablet
• Ice Cream Sandwich combined the best
characteristics of Gingerbread and
Honeycomb into a single operating system
that would work for tablets and phones
• Ice Cream Sandwich was able to bring
many of the design elements of
Honeycomb to smartphones, while refining
the Android experience
• Jelly Bean it was a faster and smoother
Android version
• Along with its Google Voice Search feature,
Jelly Bean was a jump in magnitude of
performance
• This version of Android was often referred
to as a turning point for Android, where
services and customization options met
responsive design guidelines
• KitKat looked similar to Jelly Bean;
however, due to a 512 MB size it was able
to run on a much larger array of devices
• Lollipop is the latest version of Android
being used by developers
• Lollipop and 64-bit chips provide
enhanced performance with graphics,
decoding and encoding of high-resolution
video, and algorithms for facial recognition
and speech interaction
1.2 Java vs. Android Java
• A large number of Java libraries are available
in the Android platform
• The SDK includes a debugger, software
libraries, and an emulator for an Android
device
Differences between the Java API and
the Android API
• There is no Java virtual machine in the Android
platform
• Dalvik is a specialized virtual machine
• Once Java has been compiled into bytecode by the Java
compiler, it is compiled again into a proprietary
bytecode
• Bytecode loaded by the Dalvik virtual machine should
not be confused with Java bytecode
• The dex bytecode is a compact Dalvik executable
format designed for Android systems, which are
constrained in terms of memory and processor speed
• The Android SDK includes the Dalvik dx tool, used to
translate java bytecode into Dalvik bytecode
1.3 Android Studio IDE
• Android Studio is the official IDE for building
Android applications
• Developed by Google, this environment focuses
exclusively on Android development and comes
bundled with the Android Software Development
Kit, SDK
• The SDK provides developers with a packaged set
of developer tools and API libraries for building
complete applications, testing them on virtual
devices, and performing debugging and
optimization
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Java Editor
Layout Editor
Android SDK
Android SDK Archive
AVD
Gradle
1.4 The Basics of App Design
• The process for building an application
1.5 The Anatomy of an Android
Project
• A project built in Android Studio, will be
structured similar to Figure 1-6
• Project structure is organized by source code,
the application’s resources, manifest settings,
and build files
• All of these files are eventually packaged into
an apk file, which represents the final
1.5.1 Android Manifest File
• An AndroidManifest.xml, is required for every
Android application
• This file uses XML code to define specific
application information
• This information can include general
application-wide settings such as the
application’s style and launch icon.
1.5.2 Java Source Code and Activity
class files
• The Java source code of an application is
placed in the java directory of the project
structure
• A main file, often named MainActivity or
sometimes MyActivity, is a java file that is
auto-generated when the project is first built
• It may have a different name, depending on
the Android Studio version you are using
1.5.3 Drawable Resources
• The drawable folder is located in the res
directory
• res contains the application resources
• Drawable resources are image files, such as
application icons, buttons, and background
textures
Proper Scaling of Images
• Android runs on variety of devices ranging from
low-density to high-density screens
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xlarge screens are at least 960dp x 720dp
large screens are at least 640dp x 480dp
normal screens are at least 470dp x 320dp
small screens are at least 426dp x 320dp
• A density independent pixel is equivalent to one
physical pixel on a 160-dpi )dots per inch) screen.
• Conversion of dp units to screen pixels (px) is:
Px = dp * dpi/160
Generalized screen sizes
• To properly scale application images, it is best
to start with a raw resource in vector format
and generate images for each density using
the following scale:
xxhdpi – 3.0
xhdpi – 2.0
hdpi – 1.5
mdpi – 1.0 (baseline)
1.5.4 Layout XML files
• User interface screens are visually designed
and coded as XML layout files
• The design and arrangement of the elements
on the screen are implemented using XML
code in a layout file.
1.7 Model-View-Controller
• Android applications tend to rely on the
Model-View-Controller design architecture
• This architecture assigns one of three roles
that objects can play in an application
• For example, an object can be a Model, View,
or Controller
1.9 Sharing your Android Applications
• Android requires the application to be digitally
signed with a certificate
• Android uses this certificate to identify the
author
• Android apps typically use self-signed
certificates, in which the app developer holds
the certificate’s private key