This document provides an overview of the key components and architecture of the Android operating system. It discusses that Android is built on the Linux kernel and uses Java for application development. It also summarizes the main components of the Android software stack including the libraries, runtime environment, application framework, and applications. Additionally, it describes some important Android concepts like activities, intents, broadcast receivers, content providers, and services.

2. WHAT IS ANDROID?
 Open source OS
 Uses Linux kernel
 Optimized for limited-resource environment
 Apps typically written in Java
 Apps run on the Dalvik Virtual Machine

3. ANDROID – NOW
 1B users
 1.5M new users every day
 60 OEM worldwide & 300 partners
 50B downloads
 2.5B app downloads
 2.5 times higher than last year
 7x higher revenue

5. ARCHITECTURE

6. LINUX KERNEL
 Android OS is built on top of the Linux 3.x Kernel
 This Linux will interact with the hardware and contains all the es
sential hardware drivers
 Drivers are programs that control and communicate with the hardw
are
 For example, consider the Bluetooth function. All devices has a Blu
etooth hardware in it. Therefore the kernel must include a Bluetooth
driver to communicate with the Bluetooth hardware.

7. LIBRARIES
 It is this layer that enables the device to handle different types of
data.
 These libraries are written in C or C++ language and are
specific for a particular hardware.

8. LIBRARIES
 SQLite: SQLite is the database engine used in android for data
storage purposes.
 WebKit: It is the browser engine used to display HTML content.
 OpenGL: Used to render 2D or 3D graphics content to the
screen
 Media framework: Media framework provides different media
codecs allowing the recording and playback of different media
formats

9. RUNTIME
 DVM is a type of JVM used in android devices to run apps and is
optimized for low processing power and low memory
environments.
 Unlike the JVM, the Dalvik Virtual Machine doesn’t run .class
files, instead it runs .dex files.
 The Dalvik VM allows multiple instance of Virtual machine to
be created simultaneously providing security, isolation, memory
management and threading support.

10. APP FRAMEWORK
 These are the blocks that our applications directly interacts with.
 These programs manage the basic functions of phone like
resource management, voice call management etc.
 As a developer, you just consider these are some basic tools
with which we are building our applications.

11. APP FRAMEWORK
 Activity Manager: Manages the activity life cycle of applications
 Content Providers: Manage the data sharing between
applications
 Telephony Manager: Manages all voice calls. We use
telephony manager if we want to access voice calls in our
application.
 Location Manager: Location management, using GPS or cell
tower.

12. APPLICATION
 Applications are the top layer in the Android architecture and this
is where our applications are going to fit.
 Several standard applications comes pre-installed with every
device, such as:
 SMS client app
 Dialer
 Web browser
 Contact manager

13. PREREQUISITES
 Java – JDK
 Adt bundle (Eclipse + SDK)
 Android Device (optional)
 Mobile Drivers for windows

15. COMPONENTS OF ANDROID

16. ACTIVITY
 Activity is an individual user interface screen in an Android
application
 Visual elements called Views (also known as widgets) can be
placed
 The user can perform various actions by interacting with it.

17. POINTS TO REMEMBER
 The widgets in an Activity can be created in two different ways,
by pure java code and by adding XML code to define the UI.
 An application can have more than one Activity and each
Activity operates independently, but can be linked to one another
and each Activity you create must be defined in your
application’s manifest file.
 Each Activity in android will be subclass of Activity class
defined in Android SDK.

18. ANDROID PROJECT STRUCTURE
 /src
 The src folder contains the Java source code files of your
application organized into packages.
 /Android<version Number>
 The android.jar file contains all the essential libraries required for
our program.
 /ASSETS
 The assets folder is used to store raw asset files. The raw data
can be anything such as audio, video, images etc.

19. ANDROID PROJECT STRUCTURE
 /BIN
 It is where our compiled application files go. When we
successfully compile an application, this folder will contain java
class files, dex files which are executable under Dalvik virtual
machine, apk archives etc.
 /RES
 Res folder is where we store all our external resources for our
applications such as images, layout XML files, strings, animations,
audio files etc.

20. ANDROID PROJECT STRUCTURE
 /res/drawable
 The folders are to provide alternative image resources to specific
screen configurations. The resources for each screen resolutions
are stored in respective folders and the android system will choose
it according to the pixel density of the device.
 /res/layout
 XML files that defines the User Interface goes in this folder.
 /res/values
 XML files that define simple values such as strings, arrays,
integers, dimensions, colors, styles etc. are placed in this
folder.

21. ANDROID PROJECT STRUCTURE
 Android Manifest file
 It contains all the information about your application. When an
application is launched, the first file the system seeks is the
AndroidManifest file. It actually works as a road map of your
application, for the system.
 The Android Manifest file contains information about:
 Components of your application such as Activities, services etc.
 User permissions required
 Minimum level of Android API required

22. ACTIVITY LIFECYCLE

23. ACTIVITY LIFECYCLE
 Oncreate(Bundle b) :
 When we launch an Activity in Android, it first calls the onCreate()
method. This is where we do User Interface creation and
initialization of data elements. This method is provided with a
Bundle object as parameter to restore the UI state.
 onStart() :
 This is called before the Activity is being visible to the User.
Remember that Activity is still not Active.

24. ACTIVITY LIFECYCLE
 onResume() : foreground
 The Activity become visible and Active for the user to interact
with. The Activity will be at the top of the Activity stack at this point.
Now the Activity is in running /active state and is able to receive
user inputs.
 onpause() : background
 In the Active state, onPause() method will be called when the
system is about to resume another Activity on top of this one or
when the user is about to navigate to some other parts of the
system.
 It gets killed by the system under extremely low memory
conditions.

25. ACTIVITY LIFECYCLE
 onstop() :
 This is the default action when the user has pressed the back
button, or a new activity which completely covers it resumes on
top.
 onDestroy() :
 This is called and the Activity is destroyed. This is the final
method we can call before the Activity is destroyed. This occurs
either because the Activity is finishing the operation or the system
is temporarily destroying it to save space.

26. INTENTS
 If you want to invoke a new activity from your current activity,
you need to fire an intent specifying the new activity.
 And if you want to start other application from your activity,
then also you need to fire an intent.

27. EXPLICIT INTENTS
 In explicit Intent, we are highly specific. We specify which
activity should get active on receiving the intent.
Intent intent = new Intent(A.this , B.class)
startActivity(intent);

28. IMPLICIT INTENTS
 In implicit Intent we are sending a message to the Android
system to find a suitable Activity that can respond to the intent.
 For example, to open a camera, we can use an intent . If there
is more than one activity is capable of receiving the Intent, the
system presents a chooser to the user so that he can select
which Activity/Application should handle it.
Intent intent = new
Intent(MediaStore.ACTION_IMAGE_CAPTURE);
startActivity(intent);

29. BROADCAST RECEIVERS
 Broadcast receivers are one of Android application components
that is used to receive messages that are broadcasted by the
Android system or other Android applications.
 Example :
 1. Warning that the battery is getting low
 2. Change of time zone

30. CONTENT PROVIDERS
 Content providers in Android provides a flexible way to make
data available across applications. Through content providers
other applications are able to query, access or even modify the
data you’ve created, as long as your content provider allows it.
 Example :
 The contacts database. The Content provider of contacts database
allows other applications to query, read, modify, and write the
contacts info.

31. SERVICE
 A service is an Android application component that run in
background and has no visual UI.
 A service can be started by another Android application
components such as an activity or other services and it will
continue to run in the background even after the user switches
to another application.

32.  Example :
 One typical example for the use of services is a music player
application. We can use an activity to select a music track from the
SD card and to play it.
 At any time the user is able to come back to the activity and use
the seek bar to seek the track, This means that the service and
the Activity that invoked the service are not completely
independent, instead the Activity is able to fully control the Service.
 Another example for a service is the downloading of file from the
internet. It should run in the background and continue downloading
even after we switches to another applications.

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