AndroidFundamentals

Gaurav Mitra

Scope

Topics to be covered, and assessed:

I Android Fundamentals

I Android Studio Overview

I App Components (Activity, Service, Content Provider, BroadcastReceiver, Intent etc)

I User Interface or UI (View, Layouts, Input Controls, Input Events,Event Handlers, Menus, Notifications etc)

I Persistent Data Storage

COMP 2100/2500/6442 2/15

Scope

Topics beyond our scope (NOT to be covered):

I UI (Accessibility, Custom Components, Styles & Themes)

I Animation & Graphics

I Computation with Renderscript

I Media & Camera

I Connectivity (Bluetooth, NFC, Wifi P2P, USB, SIP)

I Synchronization via Cloud resources

I Web Apps

COMP 2100/2500/6442 3/15

Why Android?

I Smartphones are ubiquitous

I Four major smartphone operating systems - Android, iOS, WindowsPhone, Blackberry OS

I Android dominates the smartphone OS market share1I Q2, 2015: Android (82.8%); iOS (13.9%); Windows Phone (2.6%); Blackberry OS (0.3%); Other (0.4%)I Q2, 2014: Android (84.8%); iOS (11.6%); Windows Phone (2.5%); Blackberry OS (0.5%); Other (0.7%)

I Free and Open source2

I Supports multiple instruction-set architectures (ARM, x86 etc) and avariety of hardware platforms ranging from smartphones, tablets,laptops, set-top-boxes to watches, and soon.. cars!

I Built to run on top of the Linux kernel

I Focus on touch-based input i.e. UI is a major design priority

1http://www.idc.com/prodserv/smartphone-os-market-share.jsp.2https://source.android.com/.

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Software Construction Perspective

I Android incorporates the use of multiple software design patternsI Creating an android app requires knowledge of

I Java programmingI Adaptable software design - A single app could target many different

devicesI Responsive UI designI Security and permissionsI Mark-up languages such as XMLI Persistent storage solutions using databasesI Inter-process communication - Often between appsI Network communication

I Modularity is key in Android’s layered architecture

COMP 2100/2500/6442 5/15

Layered System Architecture

Loosely coupled layers built on top of each other3

I Application Framework: For app developers.Many developer APIs map directly to theunderlying HAL interfaces

I Binder IPC Proxies: Allows apps to make systemcalls to the System Server. This communication ishidden from the app developer

I System Services: Modular system and mediaservices

I Hardware Abstraction Layer (HAL): Definesstandard interface for the hardware vendors toimplement. Allows upper android layers to bedevice agnostic

I Linux Kernel: Special build using additions suchas wake locks

3https://source.android.com/devices/.

COMP 2100/2500/6442 6/15

Layered Software Stack

I Loosely coupled layers built on top of eachothera

I Android Framework: For app developers.Our scope is limited to this layer only.

I Android Runtime: Dalvik Java virtualmachine (VM). Most apps run on this VM

I Native Libraries: Some apps are runnatively such as core services

ahttps://source.android.com/security/index.html.

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Java Virtual Machine

I Java programs are device/processoragnostic

I Source compiled to Java bytecodeintermediate representation (IR)

I Bytecode is executed by a JVM

I JVM compiles bytecode to machine codeJust-in-time (JIT) i.e. during theexecution of the program

I JIT compilation is a combination ofAhead-of-time (AOT) compilation andinterpretation

I Machine code executed by OS on CPU

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Android’s Dalvik JVM

Design Requirements:

I Must work on resource constrained hardware - smartphones a fewyears back had limited amounts of RAM and processing power

I Application Sandbox - to ensure security, performance and reliability

I Lack of swap space

I Battery powered

COMP 2100/2500/6442 9/15

Android’s Dalvik JVM

Dalvik Design Features4:

I Every Android app runs in its own process, with its own instance ofDalvik VM

I Multiple Dalvik VM’s can run together efficiently

I Optimized intermediate representation: Dalvik Executable (.dex) -Minimal memory footprint

I dex tool compiles .class files to .dex files

I Since each app runs an instance of Dalvik, both creation andexecution of new Dalvik instances must be efficient

I Dalvik relies on the Linux kernel to provide threading and low-levelmemory management

Dalvik has now been replaced with the improved ART (Android Runtime). However,ART remains compatible with Dalvik and runs Dex bytecode5

4http://davidehringer.com/software/android/The_Dalvik_Virtual_Machine.pdf.5https://source.android.com/devices/tech/dalvik/.

COMP 2100/2500/6442 10/15

Android Code Path

I A typical smartphone has multipleprcessing elements such as a CPU, GPUand DSP

I Java code runs in the Dalvik or ART JVMwhich runs on the CPU

I How are the GPU and DSP cores used?OpenGL and Renderscript

I Renderscript code is compiled to LLVM IRbitcode

I LLVM Bitcode is JIT compiled andexecuted on the GPU or DSP

COMP 2100/2500/6442 11/15

Security Sandbox

No app, by default, has permission to perform any operations that wouldadversely impact other apps, the OS or the user6

I Android is a privilege-separated OS

I Each application runs in isolation, in a process sandbox, with its ownsystem identity (Linux UID, GID)

I Additional security provided via permissions

I Permissions enforce restrictions on specific operations that particularprocesses can perform

I Apps prevented from reading/writing user’s private data, other app’sfiles, unauthorized network access, keeping device awake etc

I The Dalvik VM is not a hard security boundary though - apps maystill execute native code using the Android NDK

6http://developer.android.com/guide/topics/security/permissions.html.

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Android Learning Resources

I Google developer docs:http://developer.android.com/guide/index.html

I API reference:http://developer.android.com/reference/packages.html

I Video training:http://developer.android.com/training/index.html

I Multiple books available

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Android Version History and API Levels7

I Android Alpha: First release - November 2007

I Android 1.0: First commercial release - API Level 1.0 - September2008

I Release schedule stabilized to two major releases every year 2010

I . . .

I Ice Cream Sandwich: Version 4.0-4.0.4 - API level 15 - October 2011- 97% of Android devices today have an API level equal or higherthan ICS

I . . .

I Lollipop: Version 5.0-5.1.1 - API level 22 - November 2014

I Marshmallow: Most recent version 6.0-6.0.1 - API level 23 - October2015

7https://en.wikipedia.org/wiki/Android_version_history.

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Assignment 1 - Overview

I Objective: Build an Android app that can be usedto create, store, edit and delete simple notes

I A good example is Google’s own app - Keepab

I Assignment1 Specification is up

I Use minimum SDK version 15

I Labs 3 and 4 will focus on Android development

I Source code to be committed via git to CECSgitlab repository

I Week 7 due date: 28/03/2016 23:59 AEDT29/03/2016 10:00 AEDT

I No commits can be pushed after this time

I Final demo due in Week 7 labs

ahttps://www.google.com/keep/.bhttps://googleblog.blogspot.com.au.

COMP 2100/2500/6442 15/15