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Mandus Elfving, IBS JavaSolutions, 2009Android

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What is Android?

Operating system and platform for mobile devices

Developed by Google and later by the Open Source Handset

Alliance

Mostly open sourced under the Apache and other open

source licenses

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Android features

Integrated browser based on the open source WebKit engine

Optimized graphics powered by a custom 2D graphics library; 3D graphics based

on the OpenGL ES 1.0 specification (hardware acceleration optional)

SQLite for structured data storage

Media support for common audio, video, and still image formats (MPEG4, H.264,

MP3, AAC, AMR, JPG, PNG, GIF)

GSM Telephony (hardware dependent)

Bluetooth, EDGE, 3G, and WiFi (hardware dependent)

Camera, GPS, compass, and accelerometer (hardware dependent)

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Architecture

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Why is Android interesting to us?

Application development is done in Java!

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Dalvik Virtual Machine

Optimized for mobile devices

Relies on the underlying OS for process separation, memorymanagement and threading

Designed to run multiple VM instances efficiently

Executes its own type of byte code in files created from Javaclass files

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Android vs. Java

Based on Apache Harmony

Supports most of the J2SE 5.0 library

Applets, printing and other irrelevant stuff

left out

Includes third party libraries, e.g.bluetooth and JSON libraries

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Application building blocks

Applications consist of components that are the entry points

of an application

Applications can use components from other applications

Four types of components:

Activities

Services

Broadcast receivers

Content providers

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Application Building Blocks con't

Components declared in AndroidManifest.xml

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Activities

Interface for one of the activities that a

user undertake in an application

Applications are (usually) built from

multiple activities

The UI for an activity is built with Views

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Services

Used for long running background processes, e.g. media

player

Can run on its own in the background and/or be operated

by an interface

Run in the main thread of the application process

Spawn thread to not block main thread

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Broadcast receivers

Components that react to system or application broadcasts

System broadcasts for example when the battery level is low

or the timezone changed

Applications can initiate broadcasts that other applications

can react to

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Content providers

Application data is by default private to the application

Content providers make an applications private data available

to other applications through a standardized API Accessed through a ContentResolver with an URI of the

content provider to use, e.g.

content://com.example.addressbook/contacts

Android ships with standard content providers for common

data types (audio, video, contacts, etc.)

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Application navigation

Components are activated by intents

Intents are asynchronous messages

Intents contain information relevant to the receiving

component, e.g. action to take and data to act on

Also contain information that the system use for finding thecomponent that should handle it

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Application navigation con't

Components can be targeted explicitly or implicitly

Intent filters define that a component can handle a specificimplicit intents

The system locates the best component to respond to an

implicit intent

Intent filters are defined in the manifest file

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Application life cycle

Tasks are groups of related activities

arranged in a stack

Tasks can be sent to the background

or moved to the foreground

Only one task and activity running atthe same time

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Application life cycle con't

When system runs low on memory applications can be killed

All applications are placed in an importance hierarchy to

determine which application to kill next

Importance is based on the components running in an

application and their state

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Application framework

Consists of a set of services and systems to help in

application development

For example used to support localized applications and to

build the graphical UI

Used by core applications such as the SMS and Contactsapplications

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Views

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Notification manager

Allows the application to notify the user when something has

happened in the background

Different kinds:

Icon in the status bar

LEDs on the device Flashing backlight, playing a sound or vibrating

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Security

Applications are signed with a certificate

Applications run in their own process with a unique user id

Permissions restrict access to the data on the device

Permissions granted by user on installation of application

Permissions that application need and declaration of custom

permissions is done in the application manifest file

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Development environment

Android SDK

Command-line tools

Eclipse with an Android plugin

Execution/debugging in an emulator

running the full OS and software stack

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More information at:http://developer.android.com/