The document provides a comprehensive overview of the Android platform, detailing its architecture, supported languages, and key components necessary for building Android applications. It explains essential concepts like intents, activities, services, and the lifecycle of components within the Android framework. Additionally, it touches on development environments, security measures, and application configuration, emphasizing the unique nature of Android applications compared to web or desktop applications.

1. Presented by On Ramp
Android
Do Androids dream of electric sheep?
Understanding the Android platform
A developers perspective

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Presented by On Ramp
Objective
Provide a high level conceptual
model for understanding how to
build Android Applications

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Presented by On Ramp
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

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

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Presented by On Ramp
Agenda
● Important concepts
– Intents
– Activities, Services, Content
Providers & Broadcast Receivers
– Resources

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Presented by On Ramp
What is
Android?
Android is a software stack for
mobile devices that includes an
operating system, middleware and
key applications

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Presented by On Ramp
Architecture

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Presented by On Ramp
Architecture
● Linux Layer
– Based on Linux,
– Source now part of mainline Linux
V3.3
– Linux security, process
management & networking

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Presented by On Ramp
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

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Presented by On Ramp
Architecture
● Core libraries written in C/C++
– Android runtime – Dalvik
– Services exposed via application
layer,
– Reuses open source components –
SQLite, FreeType etc

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Presented by On Ramp
Architecture
● Framework layer
– What your application interacts
with,
– API calls to framework services,
– Key concepts to grok Android API

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Presented by On Ramp
Architecture
YOU!
● Applicationwritten to use
services of the Android
platform

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Presented by On Ramp
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.

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

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Supported
Languages
● Second Class Citizens
– Scripting languages via Scripting
Layer for Android
– Javascript, Ruby, Python,LUA, Perl
– HTML 5 Apps
● Important – Phonegap etc

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Presented by On Ramp
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

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Presented by On Ramp
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

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Development
Environments
● Android SDK,
– Debugger
● (ADB – Andorid Debugger Bridge)
– Libraries
– Emulator
● Supported IDE – Eclipse
– ADT plugin

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Development
Environments
● Other IDE support
– NetBeans
– IntelliJ
– Command line/text editor
● Build tool
– Ant (official)

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Presented by On Ramp
Development
Environments
● Build tool
– Maven (support from
springsource)
● Android applications have
a directory structure
– Naming of directories is
important especially for
resources

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Presented by On Ramp
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

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Core
Components
● Notifications
– System notifications

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High Level
Overview
● Different from web or desktop
applications,
● Android in control of/manages
application,
– Constrained environment,
– Memory management,
– Power usage etc

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Presented by On Ramp
High Level
Overview
● Components interact with one
another indirectly.
● Android controls creation, life
cycle of components

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Presented by On Ramp
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

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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

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Presented by On Ramp
High Level
Overview
● Activity 2 & Activity 3 may be
from different applications
Task Stack

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Presented by On Ramp
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

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Presented by On Ramp
Intents
● Intents
– can be specific -i.e require specific
class or
– Ask for any activity that provides
required service
● e.g view web page

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Presented by On Ramp
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

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Presented by On Ramp
Components
Data Sharing
● How do components pass data
between each other?
– Bundles/Extra = can add data that
needs to be transferred with Intent

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Presented by On Ramp
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

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Presented by On Ramp
Android
Where to start?
Start coding Activity components

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Activities
● Main entry point for application,
● Configures user interface and
handles events,
● Each activity has one window in
which to draw,

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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

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Activity UI
Layout
●
ADT plugin provides designer
● Similar to XHTM:

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Activity
Lifecycle

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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

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Presented by On Ramp
Activities
Screen Flow
● API Calls -
– startActivity(Intent)
– startActivityForResult(Intent)

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Presented by On Ramp
Resources
● Resources are static content
● Resources are managed by
generated code
● Layout definitions
● Images
● String constants
● Resource ids

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Presented by On Ramp
Resources
● Resources are defined in
● xml files,
● Images in folders
– Resources directory = res
– Naming of directories is important

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Presented by On Ramp
Application
Configuration
● Applications are groupings of
components
– Activities,
– Services
– Broadcast receivers
– Content provider

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Presented by On Ramp
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

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Presented by On Ramp
Security
● Linux layer
– process level security,
– File level security
● Application layer
– Request permission from user to
access services
– manifest.xml <use-permission>

45. 1 May 2013 Presented by On Ramp
Presented by On Ramp
Contact Info
● On Ramp Web Site
– http://www.onramp.mobi
● Social Networks -
– Twitter @mxc4
– G+ MClarke4
● Email:
– support@onramp.mobi
– mark@onramp.mobi