Introduction to Android Development

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

1 May 2013 Presented by On Ramp
Objective
Provide 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!
● Applicationwritten 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

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

Development
Environments
● 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
● On Ramp Web Site
– http://www.onramp.mobi
● Social Networks -
– Twitter @mxc4
– G+ MClarke4
● Email:
– support@onramp.mobi
– mark@onramp.mobi

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