Android Introduction by Kajal

This tutorial has been prepared for the
beginners to help them understand basic
Android programming. After completing
this tutorial you will find yourself at good
at primary level in Android programming
from where you can take yourself to next
levels.
ANDROID
Development Tutorial
Kajal Jain [Kucheriya]

Android Tutorial By Kajal Jain 1
Overview
What is Android?
Android is an open source and Linux-based Operating System for mobile devices such as smartphones and
tablet computers. Android was developed by the Open Handset Alliance, led by Google, and other companies.
Android offers a unified approach to application development for mobile devices which means developers need
only develop for Android, and their applications should be able to run on different devices powered by Android.
The first beta version of the Android Software Development Kit (SDK) was released by Google in 2007 where as
the first commercial version, Android 1.0, was released in September 2008.
On June 27, 2012, at the Google I/O conference, Google announced the next Android version, 4.1 Jelly Bean. Jelly
Bean is an incremental update, with the primary aim of improving the user interface, both in terms of
functionality and performance.
The source code for Android is available under free and open source software licenses. Google publishes most
of the code under the Apache License version 2.0 and the rest, Linux kernel changes, under the GNU General
Public License version 2.
Features Description
Beautiful UI Android OS basic screen provides a beautiful and intuitive user interface
Connectivity GSM/EDGE, IDEN, CDMA, EV-DO, UMTS, Bluetooth, Wi-Fi, LTE, NFC and
WiMAX.
Storage SQLite, a lightweight relational database, is used for data storage purposes.
Media support H.263, H.264, MPEG-4 SP, AMR, AMR-WB, AAC, HE-AAC, AAC 5.1, MP3, MIDI,
Ogg Vorbis, WAV, JPEG, PNG, GIF, and BMP
Messaging SMS and MMS
Web browser Based on the open-source WebKit layout engine, coupled with Chrome's V8
JavaScript engine supporting HTML5 and CSS3.
Multi-touch Android has native support for multi-touch which was initially made
available in handsets such as the HTC Hero.
Multi-tasking User can jump from one task to another and same time various application
can run simultaneously.
Resizable widgets Widgets are resizable, so users can expand them to show more content or
shrink them to save space
Multi-Language Supports single direction and bi-directional text.
GCM Google Cloud Messaging (GCM) is a service that lets developers send short
message data to their users on Android devices, without needing a
proprietary sync solution.
Wi-Fi Direct A technology that lets apps discover and pair directly, over a high-bandwidth
peer-to-peer connection.
Android Beam A popular NFC-based technology that lets users instantly share, just by
touching two NFC- enabled phones together.

Architecture
Android operating system is a stack of software components which is roughly divided into five sections and
four main layers as shown below in the architecture diagram.
Linux kernel
At the bottom of the layers is Linux - Linux 2.6 with approximately 115 patches. This provides basic system
functionality like process management, memory management, device management like camera, keypad, display
etc. Also, the kernel handles all the things that Linux is really good at such as networking and a vast array of
device drivers, which take the pain out of interfacing to peripheral hardware.
Libraries
On top of Linux kernel there is a set of libraries including open-source Web browser engine WebKit, well
known library libc, SQLite database which is a useful repository for storage and sharing of application data,
libraries to play and record audio and video, SSL libraries responsible for Internet security etc.

Advanced Android Libraries
The core libraries provide all the functionality you need to start creating applications for Android, but it won’t
be long before you’re ready to delve into the advanced APIs that offer the really exciting functionality.
Android hopes to target a wide range of mobile hardware, so be aware that the suitability and implementation
APIs will vary depending on the device upon which they are implemented.
Android Runtime
This is the third section of the architecture and available on the second layer from the bottom. This section
provides a key component called Dalvik Virtual Machine which is a kind of Java Virtual Machine specially
designed and optimized for Android.
The Dalvik VM makes use of Linux core features like memory management and multi-threading, which is
intrinsic in the Java language. The Dalvik VM enables every Android application to run in its own process, with
its own instance of the Dalvik virtual machine.
The Android runtime also provides a set of core libraries which enable Android application developers to write
Android applications using standard Java programming language.
Application Framework
The Application Framework layer provides many higher-level services to applications in the form of Java
classes. Application developers are allowed to make use of these services in their applications.
The Android framework includes the following key services:
 Activity Manager – Controls all aspects of the application lifecycle and activity stack.
 Content Providers – Allows applications to publish and share data with other applications.
 Resource Manager – Provides access to non-code embedded resources such as strings, color settings and
user interface layouts.
 Notifications Manager – Allows applications to display alerts and notifications to the user.
 View System – An extensible set of views used to create application user interfaces.
 Package Manager – The system by which applications are able to find out information about other
applications currently installed on the device.
 Telephony Manager – Provides information to the application about the telephony services available on
the device such as status and subscriber information.
 Location Manager – Provides access to the location services allowing an application to receive updates
about location changes.
Applications
You will find all the Android application at the top layer. You will write your application to be installed on this
layer only. Examples of such applications are Contacts Books, Browser, Games etc.

Application Components
Application components are the essential building blocks of an Android application. These components are
loosely coupled by the application manifest file AndroidManifest.xml that describes each component of the
application and how they interact. There are following four main components that can be used within an
Android application:
Components Description
Activities: They dictate the UI and handle the user interaction to the smartphone screen
Services: They handle background processing associated with an application.
Broadcast Receivers: They handle communication between Android OS and applications.
Content Providers: They handle data and database management issues.
Activities
An activity represents a single screen with a user interface. For example, an email application might have one
activity that shows a list of new emails, another activity to compose an email, and another activity for reading
emails. If an application has more than one activity, then one of them should be marked as the activity that is
presented when the application is launched.
An activity is implemented as a subclass of Activity class as follows:
public class MainActivity extends Activity
{
}
Services
A service is a component that runs in the background to perform long-running operations. For example, a
service might play music in the background while the user is in a different application, or it might fetch data
over the network without blocking user interaction with an activity.
A service is implemented as a subclass of Service class as follows:
public class MyService extends Service
{
}

Broadcast Receivers
Broadcast Receivers simply respond to broadcast messages from other applications or from the system. For
example, applications can also initiate broadcasts to let other applications know that some data has been
downloaded to the device and is available for them to use, so this is broadcast receiver who will intercept this
communication and will initiate appropriate action.
A broadcast receiver is implemented as a subclass of BroadcastReceiver class and each message is broadcasted
as an Intent object.
public class MyReceiver extends BroadcastReceiver
{
}
Content Providers
A content provider component supplies data from one application to others on request. Such requests are
handled by the methods of the ContentResolver class. The data may be stored in the file system, the database or
somewhere else entirely. A content provider is implemented as a subclass of ContentProvider class and must
implement a standard set of APIs that enable other applications to perform transactions.
public class MyContentProvider extends ContentProvider
{
}
Additional Components
There are additional components which will be used in the construction of above mentioned entities, their
logic, and wiring between them. These components are:
Fragments: Represents a behavior or a portion of user interface in an Activity.
Views: UI elements that are drawn onscreen including buttons, lists forms etc.
Layouts: View hierarchies that control screen format and appearance of the views.
Intents: Messages wiring components together.
Resources: External elements, such as strings, constants and drawables pictures.
Manifest: Configuration file for the application.

Hello World Example
Let us start actual programming with Android Framework. Before you start writing your first example using
Android SDK, you have to make sure that you have setup your Android development environment properly as
explained in Android - Environment Setup tutorial. I also assume that you have a little bit working knowledge
with Eclipse IDE.
So let us proceed to write a simple Android Application which will print "Hello World!".
Create Android Application the first step is to create a simple Android Application using Eclipse IDE. Follow the
option File -> New -> Project and finally select Android New Application wizard from the wizard list. Now name
your application as HelloWorld using the wizard window as follows:

Next, follow the instructions provided and keep all other entries as default till the final step. Once your project
is created successfully, you will have following project screen:

Anatomy of Android Application
Before you run your app, you should be aware of a few directories and files in the Android project:

S.N. Folder, File & Description
1 Src This contains the .java source files for your project. By default, it includes an
MainActivity.javasource file having an activity class that runs when your app is
launched using the app icon.
2 gen This contains the .R file, a compiler-generated file that references all the
resources found in your project. You should not modify this file.
3 bin This folder contains the Android package files .apk built by the ADT during
the build process and everything else needed to run an Android application.
4 res/drawable-hdpi This is a directory for drawable objects that are designed for
high-density screens.

5 res/layout This is a directory for files that define your app's user interface.
6 res/values This is a directory for other various XML files that contain a
collection of resources, such as strings and colors definitions.
7 AndroidManifest.xml This is the manifest file which describes the fundamental
characteristics of the app and defines each of its components.
Following section will give a brief overview few of the important application files. The Main Activity File The
main activity code is a Java file MainActivity.java. This is the actual application file which ultimately gets
converted to a Dalvik executable and runs your application. Following is the default code generated by the
application wizard for Hello World! application:
Here, R.layout.activity_main refers to the activity_main.xml file located in the res/layout folder. The onCreate()
method is one of many methods that are fi red when an activity is loaded.

The Manifest File
Whatever component you develop as a part of your application, you must declare all its components in a
manifest file called AndroidManifest.xml which ressides at the root of the application project directory. This file
works as an interface between Android OS and your application, so if you do not declare your component in
this file, then it will not be considered by the OS. For example, a default manifest file will look like as following
file:
Here <application>...</application> tags enclosed the components related to the application.
Attributeandroid:icon will point to the application icon available under res/drawable-hdpi. The application
uses the image named ic_launcher.png located in the drawable folders The <activity> tag is used to specify an
activity and android:name attribute specifies the fully qualified class name of the Activity subclass and the
android:label attributes specifies a string to use as the label for the activity. You can specify multiple activities
using <activity> tags. The action for the intent filter is named android.intent.action.MAIN to indicate that this
activity serves as the entry point for the application. The category for the intent-filter is
namedandroid.intent.category.LAUNCHER to indicate that the application can be launched from the device's
launcher icon. The @string refers to the strings.xml file explained below. Hence, @string/app_name refers to
theapp_name string defined in the strings.xml fi le, which is "HelloWorld". Similar way, other strings get
populated in the application.
Following is the list of tags which you will use in your manifest file to specify different Android application
components:
<activity>elements for activities
<service> elements for services
<receiver> elements for broadcast receivers
<provider> elements for content providers

The Strings File
The strings.xml file is located in the res/values folder and it contains all the text that your application uses. For
example, the names of buttons, labels, default text, and similar types of strings go into this file. This file is
responsible for their textual content. For example, a default strings file will look like as following file:
The Layout File
The activity_main.xml is a layout file available in res/layout directory, that is referenced by your application
when building its interface. You will modify this file very frequently to change the layout of your application.
For your "Hello World!" application, this file will have following content related to default layout:
This is an example of simple RelativeLayout which we will study in a separate chapter. The TextView is an
Android control used to build the GUI and it have various attribuites like
android:layout_width,android:layout_height etc which are being used to set its width and height etc. The
@string refers to the strings.xml file located in the res/values folder. Hence, @string/hello_world refers to the
hello string defined in the strings.xml fi le, which is "Hello World!".
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">FirstApp</string>
<string name="action_settings">Settings</string>
<string name="hello_world">Hello world!</string>
</resources>

Running the Application
Let's try to run our Hello World! application we just created. I assume you had created your AVD while doing
environment setup. To run the app from Eclipse, open one of your project's activity files and click Run icon
from the toolbar. Eclipse installs the app on your AVD and starts it and if everything is fine with your setup and
application, it will display following Emulator window:
Congratulations!!! you have developed your first Android Application and now just keep following rest of the
tutorial step by step to become a great Android Developer.
All the very best.

Android Introduction by Kajal

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