Introduction to Android Development

Presented by On Ramp

Android

Do Androids dream of electric sheep?

Understanding the Android platformA developers perspective

1 May 2013 Presented by On Ramp Presented by On Ramp

ObjectiveProvide a high level conceptual model for understanding how to

build Android Applications


About Me

● South African open source solutions integrator,– Java developer,

– Drupal developer,

– Loves Linux,

● On Ramp– Ethiopian Company

● Linux, Java, Android training and development house● Specialising in mobile telecoms space


Agenda● Android Architecture● Supported Languages● Dalvik VM● Development Environments● Components – Building Blocks ● High Level Overview


Agenda● Important concepts

– Intents

– Activities, Services, Content Providers & Broadcast Receivers

– Resources


What is Android?

Android is a software stack for mobile devices that includes an

operating system, middleware and key applications


Architecture


Architecture

● Linux Layer– Based on Linux,

– Source now part of mainline Linux V3.3

– Linux security, process management & networking


Architecture

● Linux Layer– Each app has its own Linux user,

– All files and resources owned by app user,

– Other processes, app cannot access other app's files/resources


Architecture

● Core libraries written in C/C++– Android runtime – Dalvik– Services exposed via application

layer,

– Reuses open source components – SQLite, FreeType etc


Architecture

● Framework layer – What your application interacts

with,

– API calls to framework services,

– Key concepts to grok Android API


Architecture

YOU!

● Application written to use services of the Android platform


Supported

Languages● Android applications can be

written in – Java

● Supports a subset of Java API,● Can use most Java libraries,

– C/C++ using native development kit

● Should only be when performance is an issue.


Supported Languages

– C/C++ using native development kit● Used to write components called from

Java


Supported Languages

● Second Class Citizens– Scripting languages via Scripting

Layer for Android– Javascript, Ruby, Python,LUA, Perl

– HTML 5 Apps● Important – Phonegap etc


Dalvik● Dalvik is a process

virtual machine– Application written in

Java

– Complied to Java byte code (.class files)

– Converted into Dalvik compatible files (.dex) when packaged


Dalvik● Why Dalvik?

– More compact & memory efficient than .class files

– Each application runs in its own process,

– Each process gets it own VM

– Packaging (apk) files are zipped .dex files


Development Environments

● Android SDK,– Debugger

● (ADB – Andorid Debugger Bridge)

– Libraries

– Emulator

● Supported IDE – Eclipse– ADT plugin



● Other IDE support– NetBeans

– IntelliJ

– Command line/text editor

● Build tool – Ant (official)



● Build tool – Maven (support from

springsource)

● Android applications have a directory structure– Naming of directories is

important especially for resources


Core Components

● Activities– UI Layer– Similar to UI controller for web apps

● Services– Provides services to other applications, no ui, run in

background

● Content Providers– Used to pass information between applications

● Broadcast receivers– Listen to system events and broad cast and react


Core Components

● Notifications– System notifications


High Level Overview

● Different from web or desktop applications,

● Android in control of/manages application,– Constrained environment,

– Memory management,

– Power usage etc

●


High Level Overview

● Components interact with one another indirectly.

● Android controls creation, life cycle of components


High Level Understanding

● Applications can use components from other apps,

● Task Stack -– Android places UI components

(Activities), maybe from different apps, onto a task stack, as user navigates through an application


High Level Overview

● Component life cycle controlled by platform,

● Platform provides life cycle methods to allow components to react to changes in life cycle– onStart

– onResume

– onPause etc


High Level Overview

● Activity 2 & Activity 3 may be from different applications

Task Stack


High Level Overview

● How does your activity request new component from Android?– API calls

– Via Intents ● Define what you would like to have

happen next,● Pass data to next activity● Receive data back


Intents● Intents

– can be specific -i.e require specific class or

– Ask for any activity that provides required service

● e.g view web page


Intents● Intent made up of

– Action: view web page,place call

– Category: what attribute the component must have for your action e.g must display home screen

– Extra: data to pass between components


Components Data Sharing

● How do components pass data between each other?– Bundles/Extra = can add data that

needs to be transferred with Intent


Summary

UI components belong to a task

Platform creates components on you behalf

API used to request component creation

Components have a life cycle

Components are building blocks for your app

Other apps may use your components


Android

Where to start?

Start coding Activity components


Activities● Main entry point for application,

● Configures user interface and handles events,

● Each activity has one window in which to draw,


Activities● UI layout is best done with xml

resource files,● Java code for handling events &

setting up UI● UI widgets extend View class

– Views are the display classes used by an activity


Activity UI Layout

● ADT plugin provides designer

● Similar to XHTM:


Activity Lifecycle


Activities Screen Flow

● Flow between activities or screens is not direct,

● Application framework handles this for you

● You ask framework to create next screen you wish to display


Activities

Screen Flow ● API Calls -

– startActivity(Intent)

– startActivityForResult(Intent)


Resources

● Resources are static content● Resources are managed by

generated code● Layout definitions● Images● String constants● Resource ids


Resources

● Resources are defined in ● xml files,● Images in folders

– Resources directory = res

– Naming of directories is important


Application Configuration

● Applications are groupings of components– Activities,

– Services

– Broadcast receivers

– Content provider


Application Configuration

● Apps are defined via manifest.xml– <application> defines

● launcher activity for app,● what intents your components are created to

handle

– <uses-permission> to identify what services your application requires access to


Security● Linux layer

– process level security,

– File level security

● Application layer– Request permission from user to

access services– manifest.xml <use-permission>


Contact Info

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● Email: – [email protected]– [email protected]

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Technology

Introduction to Android Development