Android OS : Core Concepts

Dr. Jeyakesavan VeerasamySr. Lecturer

University of Texas at Dallasjeyv@utdallas.edu

Agenda

• Introduction to Android devices• Environment overview• Android concepts• Application components– Activities, Services, Content providers, Broadcast

receivers• “Hello” application• Summary

Development Environment

• Java Development Kit (JDK) • Eclipse IDE• Android Development Tools (ADT) plug-in• SDK starter package– Platforms (1.0, 2.0, 3.0, 4.1, …)– Tools (debug, …)

Reference: http://developer.android.com/sdk/installing.html

JDK

Eclipse ADTPlug-in

AndroidSDK

Development Process for

Android Applications

Android Architecture

Android Runtime Environment

• Dalvik VM for each application• common Linux kernel

JRE

x.class y.class

Linux kernel

VM VM

APP APP…

Basics: UNIX security

• compare it with Windows security

Application Security

• Android operating system is based on multi-user Linux system.

• Each application is treated as a different user. Each application uses unique Linux user ID.

• Every application runs as a Linux process.

Application security …

• It's possible to arrange for two applications to share the same Linux user ID, in which case they are able to access each other's files – can run as same Linux process and share the same VM (applications use same certificate).

• An application can request permission to access device data such as the user's contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and more. All application permissions must be granted by the user at install time.

Processes & Threads

• Every application runs in its own process and all components of the application run in that process, by default -- UI thread

• Any slow, blocking operations in an activity should be done in a new thread, to avoid slowing down the user interface.– If application does not respond in 5 seconds, "

application not responding" (ANR) dialog appears.

Process lifecycle: Importance Hierarchy

• Foreground process• Visible process• Service process• Background process• Empty process

“Lower importance” tasks may be killed by Android – why?How to select a lucky one from a pool?

IPC

• Remote procedure calls (RPCs)

Android Application components

• Activities - front-end UI screens• Services – back-end support• Content providers – application data – SQLite, web or SD card

• Broadcast receivers – handle system events

Activitating Components: Intent

Basics: Data Exchange

A1

A3

A2

A4

Basics: Data Exchange

• Binary or text data XML or JSON …

• Independent data checkers tools available.A1

A3

A2

A4

Sample XML data file

Text format:Belgian Waffles, 5.95, two of our famous Belgian Waffles with plenty of real … , 650Strawberry Belgian Waffles, 7.95, light Belgian waffles covered with …., 900

Application info: Manifest file

• Declare components• Declare application requirements• Application Resources?

Activity lifecycle: 3 states

• Resumed or Running• Paused• Stopped

State machine

Code

Service Lifecycle

User Interface Design

XML Layouts

• Declare UI elements in XML. Android provides a straightforward XML vocabulary that corresponds to the View classes and subclasses.

• Instantiate layout elements at runtime. Your application can create View and ViewGroup objects (and manipulate their properties) programmatically.

Application Resources

Building & running Android app

Program to say “Hello!”

Native Development Kit (NDK)

• Use C/C++ for development• primarily for performance critical components

Summary

• Clean, sophsticated, yet reasonably simple.• Android requires strong Java skills – heavy use of

derived classes (inheritance).• Development: Java code & XML definitions• Reference: http://

developer.android.com/sdk/installing.html• Install Android development environment and

play with a few examples or try your own ideas!• Marketable skill in the industry!

More references

• http://www.vogella.de/articles/AndroidIntent/article.html• http://developer.android.com/resources/browser.html?tag=sa

mple

Questions & Answers

jeyv@utdallas.edu