04 Development and Runtime Platforms: Overview, J2ME, iOS ...lia.disi.unibo.it/Courses/sm1819-info/lucidi/04-Platforms(1x).pdf · Development/Runtime Platforms –Mobile Systems M

Development/Runtime Platforms – Mobile Systems MDevelopment/Runtime Platforms – Mobile Systems M 11

Mobile Systems M

Alma Mater Studiorum – University of Bologna

CdS Laurea Magistrale (MSc) in

Computer Science Engineering

Mobile Systems M course (8 ECTS)II Term – Academic Year 2018/2019

04 – Development and Runtime Platforms:

Overview, J2ME, iOS, and Android

Paolo Bellavista

[email protected]

http://lia.disi.unibo.it/Courses/sm1819-info/

http://lia.disi.unibo.it/Staff/PaoloBellavista/

mailto:[email protected]

http://lia.disi.unibo.it/Courses/sm1819-info/

http://lia.disi.unibo.it/Staff/PaoloBellavista/

Development/Runtime Platforms – Mobile Systems M 2

Overview on

Development/Runtime Platforms

Many solutions have been proposed in the literature for

development/runtime support of mobile systems

middleware and applications. Why?

❑ Heterogeneity and fragmentation

❑ Market-driven choice

❑ Very heterogeneous and differentiated characteristics

of available devices, “platforms”, and app requirements

Plethora of solutions: Symbian, Palm, RIM, Maemo/Meego, iOS,

Android, Java Mobile Edition (J2ME), .NET Compact Framework (CF),

Python, Lazarus, Brew, Flash Lite, Web runtime environment (micro-

browser, HTML5, XHTML/CSS, JavaScript, Mobile Ajax, …), …

Let’s try to put in order…

Which involved layers?


❑ Operating system layer (e.g., is Android an operating system?)

❑ Runtime execution support layer (frameworks,

containers, virtual machines, …)

❑ Development support layer - SDK (libraries, support

components, containers, …)

Again, layers with NO clear borders and NOT easily disjoint…

❑ Mainly at OS layer: Symbian, Palm, RIM (BlackBerry),

Maemo/Meego, iOS, Linux?, …

❑ Mainly at runtime execution support layer: Kernel-based Virtual

Machine (KVM) or Dalvik Virtual Machine for Java, Common Language

Runtime (CLR) for .NET, Flash Lite, Web runtime environment

Overview on



❑ Mainly at development support layer: J2ME world, .NET CF

world, ActionScript for Flash Lite, Android world, Web runtime

environment

Two primary approach categories:

❑ Based on native applications

❑ Based on Web integration (in particular, see standardization

efforts associated with HTML5)

Let’s start with the first approach, by choosing to have a rapid

overview on 4 main families of solutions: J2ME, .NET CF,

Flash Lite, and Android

Overview on



Overview on J2ME, .NET CF,

Flash Lite, and Android


J2ME in a Single Slide

❑ Java edition for resource-limited devices (smart phones, set-

top boxes) – http://www.oracle.com/technetwork/java/

embedded/javame/index.html

❑ Bytecode is run over Kernel-based Virtual Machines

(KVM), full OS independency

❑ Configuration concept: minimum feature set for VM + support

libraries for a horizontal family of devices

➢ Connected Limited Device Configuration (CLDC)

❑ Profile concept: specialized libraries for the characteristics of a

given type/class of devices

➢ Mobile Information Device Profile (MIDP), on top of CLDC

❑ Java apps over CLDC/MIDP are called MIDlet

Do you already know what Java Community Process (JCP) and Java

Specification Request (JSR) are?

http://www.oracle.com/technetwork/java/embedded/javame/index.html


.NET CF in a Single Slide

❑ Subset of .NET platform (around 30% of classes and features) for

MS Windows Mobile devices

❑ Exploitation of Common Language Runtime (CLR); in

principle, support for different OSs and different programming

languages (actually only WinMobile, C#, and VB.NET)

❑ Idea of smooth transition from desktop app development to

mobile app development, anyway pushed by a big vendor with a

large community of developers

❑ Cost associated with intermediate code execution (Common

Intermediate Language – CIL)

❑ Relatively high cost in terms of memory footprint

❑ It has NO “fragmentation” problems, differently from J2ME


Adobe Flash Lite in a Single Slide

❑ Proprietary technology that was popular for the

development of multimedia contents and games

❑ Basically, support for vectorial graphics and

animations; add-ons of application and presentation logics

via ad-hoc programming language, i.e., ActionScript, which runs over a dedicated runtime support

❑ Smooth transition for expert Flash developers

❑ Incomplete solution for stand-alone full-fledged apps; NO

ambition of general purpose solution

❑ Strong integration with low-level capabilities of devices, therefore with good efficiency

❑ Limited performance due to cost of vectorial graphics management

❑ See similar approach in the Java world with JavaFX Mobile –

https://www.java.net/community/javafx

https://www.java.net/community/javafx


Android in a Single Slide

❑ Launched by Google in 2007 as an Apache free-software platform, based on Linux

❑ Applications were developed in Java and compiled intoDalvik Executable format (DEX – custom bytecode, e.g., more concise than usual .class)

❑ Quite large subset of J2SE facilities + rich library of support features (Android SDK) available for the community of developers❑ Touch screen management, local sensors (accelerometers,

gyroscopes, GPS, …), 3D graphics, advanced support for location-based services, …

❑ Also here possible? fragmentation issues due to different OS versions and to usage of different extensions of the support stack(given the potential openness of the adopted approach…)


A Comparison with a Toy Application

(Gavalas et al, IEEE Software, 2011)


A First Comparison


A First Comparison


A First Comparison


A First Comparison


A First Comparison


By delving into finer technical details:

Java 2 Micro Edition

In general terms, different editions of Java “distributions”

Central role of

the KVM +

CLDC +

MIDP stack


JSR 248:

Mobile Service Architecture (MSA)

17

Actually, more complex

and articulated

situation

Important

fragmentation

issues

MSA, in two

versions:

full (17/14) or

subset (8/9)


J2ME: Configurations and Profiles

❑ A configuration defines a minimal platform for a

horizontal group of devices

➢ Similar requirements on memory and computing power

➢ It defines Java language and virtual machine characteristics

that have to be available on the targeted group of devices

➢ “A Configuration is a specification that defines a minimum Java Platform

functionality for a family of devices. It defines the minimum number of Java

libraries, VM capabilities, Security specification, and a Generic Connection

Framework”

❑ Profile as a set of additional APIs that extend a

configuration with capabilities that are useful for a specific

group of devices➢ “A Profile is a collection of Java APIs that supplement a Configuration to

provide capabilities for a specific device group or market type”


J2ME: Defined Configurations

❑ Connected Device Configuration (CDC)

➢ Typically for devices with higher resources if compared with low-end phone devices (no more valid nowadays)

➢ For example, set-top boxes, initially some kinds of PDAs, …

❑ Connected, Limited Device Configuration (CLDC)

➢ For devices with very limited onboard resources

Virtual machine for CLDC: Sun’s Kilo Virtual Machine (KVM)➢ Small memory footprint (60K)

➢ Overall minimum memory = 160K

➢ 16/32-bit processors

➢ Processor speed = at least in the range 8-32MHz

➢ Typical hardware of CLDC configuration

For CLDC the only STRONG requirement is available memory size:➢ At least non-volatile 128K for KVM and CLDC libraries

➢ At least volatile 32K for KVM runtime


J2ME Profiles

Any profile defines requirements for a family of devices

associated with a specific vertical market

❑ It extends (with a upper overlay layer) a configuration. Always on

top of one defined configuration

❑ It defines a standardized Java platform for a device family/class

in order to achieve interoperability (effort towards the reduction of

fragmentation issues)

❑ It includes class libraries with finer granularity if compared with the

ones in a configuration

Available profiles:

❑ Mobile Information Device Profile (MIDP)

on top of CLDC. It includes additional features for GUIs, multimedia

and gaming support, end-to-end security, extended support to

network connectivity for mobile phones and entry-level PDAs


Defined J2ME Profiles(continued…)

❑ …

❑ Foundation Profileon top of CDC. Set of basic Java APIs for resource-limited devices; crucial and central factor is lack of standard GUI support

❑ Personal Profile

on top of CDC. Together with Foundation Profile, Personal Profile implements the support for development of high-end PDA applications. Personal Profile includes complete set of AWT APIs, support for applets and Xlets

❑ Personal Basis Profile

on top of CDC. It provides developers with an environment for the support of applications with network connectivity and an elementary degree of grahics support for content presentation


MIDP: Hardware Requirements

❑ Memory (in addition to the one requested by CLDC)

➢ 128K non-volatile for MIDP components

➢ 8K non-volatile for persistent application data

➢ 32K volatile for KVM

❑ Display

➢ Screen with at least 96x54 pixels

➢ Display depth (or color depth or bit per pixel) at least equal to 1-bit

➢ Form factor of pixels (aspect ratio) = 1:1

❑ Input peripherals (one or multiple)

➢ One-handed keypad

➢ Two-handed keypad

➢ Touch screen

❑ Networking

➢ Two-way

➢ Wireless

➢ Management of intermittent connectivity

➢ Limited bandwidth


MIDP Architecture

Mobile Information Device (MID)

CLDC

MIDP

Native OS + System Software

MIDP

Applications

OEM-Specific

Applications

OEM-Specific

Classes

Device-Native

Applications

Original Equipment Manufacturer (OEM)


Class Libraries

❑ CLDC

java.lang

java.io

java.util

javax.microedition.io

❑ MIDP

javax.microedition.lcdui

javax.microedition.midlet

javax.microedition.rms


MIDP Application Model

❑ MIDP applications are called “MIDlets”❑ MIDlet model is, under many perspectives,

similar to the applet model in J2SE: component-container model and lifecycle management

❑ Also security support for applications that share resources/data (via MIDlet Suite)

❑ MIDlet lifecycle is described as state transitions, indicated as:➢ Start – resource acquisition and execution start➢ Pause – resource release and entrance in the

“wait” state➢ Destroy – resource release, thread destruction,

and ending of all activities

➢ Java Application Manager (JAM) for MIDlet lifecycle management

Pause

Active

Destroyed

sta

rtA

pp

de

str

oyA

pp

pa

us

eA

pp

de

str

oyA

pp


Typical J2ME Support Stack

Mobile Information

Device Profile

KVM

CLDC = KVM + J2ME Core

API in this

example DSP chip(e.g., ARM)

J2ME core APIs

Your

MIDletYellow pages, train timetable and ticketing, games, …

UI, HTTP networking, ...

Thread support,

no floating point…

32-bit RISC, 256K ROM, 256K Flash, 64K RAM

KVM + CLDC + MIDP: applications are developed and run on top

of this standardized stack, independently from OS and hw

details


CLDC/MIDP: some Detail about the Primary Packages

❑ Package➢ javax.microedition.io

➢ javax.microedition.lcdui (user interface for lcd displays)

➢ javax.microedition.midlet

➢ javax.microedition.rms (persistent storage)

❑ Widget support for user GUIs➢ Form, TextField, TextBox, DateField, List, Image, Gauge, Alert,

Canvas, Graphics, Display

➢ Two different types of APIs (lower and higher abstraction layers) for GUI management

▪ High level for widget, scrolling, ...

▪ Low level for graphics fine-grained GUI control

❑ Classes for event management – Command and CommandListener

❑ Most relevant: is obvious for all, isn’t it ☺?, which is the underlying threading model?


Usual “Hello World”

as a MIDlet

import javax.microedition.lcdui.*;

import javax.microedition.midlet.*;

public class HiMIDlet extends MIDlet {

private TextBox textbox;

public HiMIDlet() {

textbox = new TextBox ("", "Hello World!", 20, 0);

}

public void startApp() {

Display.getDisplay(this).setCurrent(textbox);

}

public void pauseApp() {}

public void destroyApp(boolean unconditional) {}

}


MIDlet:

Simple GUI Managementimport javax.microedition.midlet.*;import javax.microedition.lcdui.*;

public class HelloWorld extends MIDlet implements CommandListener {

private Form mainscreen;private Form detailsscreen;private Display myDisplay;private Command exitCommand;private Command resetCommand;private Command detailsCommand;

public HelloWorld(){

myDisplay = Display.getDisplay(this);mainscreen = new Form("Hello World");detailsCommand = new Command("Details",Command.SCREEN, 1);resetCommand = new Command("Reset",Command.SCREEN,1);exitCommand = new Command("Exit", Command.EXIT, 1);

}


StringItem strItem = new StringItem("Hello", " World");

mainscreen.addCommand(detailsCommand);

mainscreen.addCommand(resetCommand);

mainscreen.addCommand(exitCommand);

mainscreen.append(strItem);

mainscreen.setCommandListener(this);


myDisplay.setCurrent(mainscreen); }

protected void pauseApp() { }

protected void destroyApp(boolean unconditional) { }

MIDlet:

Simple GUI Management


public void commandAction(Command c, Displayable s) {

if (c == exitCommand) {

destroyApp(false);

notifyDestroyed(); }

else if (c == detailsCommand) {

detailsscreen = new Form("Details");

detailsscreen.addCommand(resetCommand);

detailsscreen.setCommandListener(this);

myDisplay.setCurrent(detailsscreen); }

else if (c == resetCommand) {

myDisplay.setCurrent(mainscreen); }

}

}

MIDlet:

Simple GUI Management


import java.io.*;

import javax.microedition.io.*;

import javax.microedition.midlet.*;

import javax.microedition.lcdui.*;

public class PrimitiveMIDlet extends MIDlet

implements CommandListener {

private Display mDisplay;

private Form mMainForm;

private Command mExitCommand, mConnectCommand;


mDisplay = Display.getDisplay(this);

if (mMainForm == null) {

mMainForm = new Form("PrimitiveMIDlet");

mMainForm.append(new StringItem("", "Select Connect to

make a network connection"));

mExitCommand = new Command("Exit", Command.EXIT, 0);

mConnectCommand = new Command("Connect",

Command.SCREEN, 0);

MIDlet:

a more Realistic Example


mMainForm.addCommand(mExitCommand);

mMainForm.addCommand(mConnectCommand);

mMainForm.setCommandListener(this); }

mDisplay.setCurrent(mMainForm); }


if (c == mExitCommand) notifyDestroyed();

else if (c == mConnectCommand) connect();

}

private void connect() {

String url = getAppProperty("NetworkThreading.URL");

try { //interroga server e riceve risposta

HttpConnection hc = (HttpConnection)Connector.open(url);

InputStream in = hc.openInputStream();

int contentLength = (int)hc.getLength();

if (contentLength == -1) contentLength = 255;

byte[] raw = new byte[contentLength];

int length = in.read(raw);

MIDlet:



in.close();

hc.close();

// Show the response to the user.

String s = new String(raw, 0, length);

Alert a = new Alert("Response", s, null, null);

a.setTimeout(Alert.FOREVER);

mDisplay.setCurrent(a, mMainForm); }

catch (IOException ioe) { Alert a = new Alert(

"Exception", ioe.toString(), null, null);

a.setTimeout(Alert.FOREVER);

mDisplay.setCurrent(a, mMainForm); }

}


public void destroyApp(boolean unconditional) {}

}

MIDlet:


Which possible issues in a real usage scenario?


MIDlet:


Which possible issues in a real usage scenario?

❑ NO GUI feedback during the time interval needed for connection

establishment => «no-waiting» user that generates other useless

commands…

❑ Most relevant: threading model

➢ System threads are “offered” for MIDlet execution

➢ The only threads fully and exclusively owned by a MIDlet

are the ones that MIDlet explicitly instantiates

➢ As in other technologies, e.g., for GUI management: a system

thread works as event dispatcher; event managers have to

rapidly return control in order not to block the MIDlet

interface

Therefore, the «right and sound» solution would be…



if (c == mExitCommand)

notifyDestroyed();

else if (c == mConnectCommand) {

Thread t = new Thread() {

public void run() {

connect(); }

};

t.start(); }

}

MIDlet:


Which possible issues in this case?


SingleWorker class…

public synchronized void run() {

while (mTrucking) {

try { wait(); }

catch (InterruptedException ie) {}

if (mTrucking) connect(); }

}

public synchronized void go() {

notify(); }

SingleMIDlet classimport java.io.*;

…

public class SingleMIDlet extends MIDlet implements CommandListener {

private Display mDisplay;

private Form mMainForm, mWaitForm;

private SingleWorker mWorker;

private Command mExitCommand, mConnectCommand, mCancelCommand;

…

MIDlet:




mDisplay = Display.getDisplay(this);

if (mMainForm == null) {

//preparazione form

…

mWorker = new SingleWorker(this, url);

mWorker.start(); }

mDisplay.setCurrent(mMainForm); }


if (c == mExitCommand) notifyDestroyed();

else if (c == mConnectCommand) {

mDisplay.setCurrent(mWaitForm); mWorker.go(); }

else if (c == mCancelCommand) {

mDisplay.setCurrent(mMainForm); mWorker.cancel(); }

}


public void destroyApp(boolean unconditional) {

mWorker.stop();

} …

MIDlet:



J2ME: Types of

Supported Web Connections

❑ HTTP/HTTPS➢ Simple to use

❑ XML over HTTP/HTTPSRecently most widespread usage thanks to availability of several

lightweight parsers

➢ Model: it creates object-based representation of a doc n memory, e.g., DOM

➢ Push: it parses a whole document, by distributing then events to the registered listeners, e.g., SAX

➢ Pull: it parses the document a part after the other (fragment), by returning a single element or tag

In addition, very often, exploitation of features defined in additional JSRs: among the others, JSR82 (Bluetooth), JSR179 (Location), JSR135 (Mobile Media), JSR180 (SIP), and JSR172 (Web Services)


(optional) Exercise on J2ME:How to Design a MIDlet Application

❑ Identifying the target devices

❑ Identifying the profiles that are supported by those devices

❑ Developing the application ➢ For instance, if as a MIDlet because CLDC/MIDP is supported,

application suitable for cellphones and small pagers

❑ The development environment should be integrated with CLDC/MIDP: MIDP reference implementation http://www.oracle.com/technetwork/java/index-jsp-138820.html

❑ Possibility of execution (for validation and testing purposes) over MIDP emulators➢ For example, usage of J2ME Wireless Toolkit and ktoolbar to

create a project and to design, implement, configure, and validate a MIDlet

➢ Probably you will appreciate more working with Eclipse ME http://eclipseme.org/

http://www.oracle.com/technetwork/java/index-jsp-138820.html

http://eclipseme.org/


For example, Nokia J2ME SDK


Remember:

MIDlet Upload Process

Web Page

JAM

Downloads

App

User

Selects

App

Advertise

App on

Web Page

Network TransferJava Application

Manager

(Name,

Version,

Size,

…)

Jar File

Descriptor

File


Optional Exercise on J2ME:How to Design a MIDlet Application

To design and develop a simple context-dependent

MIDlet (e.g., able to play sounds or multimedia files that are

differentiated depending on current user location), by exploiting

features of JSR 135 (known as Mobile Media API,

http://java.sun.com/products/mmapi/) and of JSR 179 (known as

Location API, different implementation more or less “easily”

available, e.g., http://code.google.com/p/openlapi/)

❑ Exploiting, as preferred, development tools and IDEs such as

JavaME Wireless Toolkit or Eclipse ME

Note that the support for “old-fashioned” technologies such

as Java ME is decreasing and decreasing…

http://java.sun.com/products/mmapi/

http://code.google.com/p/openlapi/


A Superficial Overview of

the Security Model

JME CANNOT support the regular and complete

security model of J2SE❑ The implementation of the only J2SE protection domains is

larger than the whole CLDC implementation (footprint)

Therefore, how to implement a security solution for JME?

Main guideline – to split the problem into two parts:

❑ VM-level security (low-level)

➢ Obtained via the 2-phase verifier for class files that is

included in CLDC

❑ Application-level security

➢ Sandbox model


Security:

Class File Verifier in 2 Phases

❑ Off-device verification➢ Tool for pre-verification adds a “stack map” attribute to any method

in the Java class file in order to facilitate in-device verification

➢ Pre-verification process (computationally heavyweight) is run on

server/desktop side before that the class file is downloaded on

mobile device

➢ “stack map” then helps to make more efficient the in-device

verification

▪ Faster

▪ Less code in VM and minor memory consumption

❑ In-device verification➢ Environment verification (e.g., memory requirements at runtime)

➢ Bytecode check

➢ Type check

➢ “Proper” termination, i.e., adequate and robust (e.g., no instructions

for unconditional jump)


Stack map attribute grows the size of classfile of around 5%

Security:

Class File Verifier in 2 Phases


Application-level Security:

Sandbox Model

Applications (MIDlets, but not only them) have to execute in a

close environment from where they can access only the

APIs defined by configuration, profile, and licensed classes

that are supported by the used deviceDo you remember the sandbox execution model for applets?

More specifically, MIDlet sandbox model specifies:❑ Class files have to pass an adequate verification step (to

guarantee they are valid)

❑ Only the APIs defined by CLDC, profile, and licensed extension

classes have to be available

❑ Application download occurs at so-called native layer (native

code level), mandatorily via the Java Application Manager (JAM)

❑ Forbidden to override the standard class loading mechanism

❑ Forbidden the access to the set of native functions that the VM can

instead use


Android: Architecture

Classical hierarchical architecture, structured into layers (growing complexity from bottom to top)

Layers:

❑ Linux kernel

❑ Libraries (native Linux)

+ Android runtime

(Dalvik VM + core

libraries)

❑ Application

Framework

❑ Applications


Android: Architecture

Kernel Layer❑Based on traditional Linux v3.x

kernel and evolutions❑ It introduces Hardware

Abstraction Layer (HAL)

Libraries❑ in native language (C/C++)

Android Runtime❑Execution environment for

applications, written in Java❑Based on Dalvik VM

Application Framework❑ It provides applications with

advanced services, encapsulated in Java objects,

Application❑Core Apps: provided by the

«initial» onboard system❑Developers’ written apps…

Development/Runtime Platforms – Mobile Systems M

Android:

Elements about Version Evolution

Ice Cream Sandwich 4.0.1 (October 2011)❑Linux kernel 3.0.1; customizable launcher; "Contacts" app fully integrated with main social network applications; Android Beam (data exchange via NFC); Wi-Fi Direct, etc. etc.


Android:


Jelly Bean 4.1.1 (July 2012)❑Linux kernel 3.1.10; new features for picture/video sharing via NFC; advanced voice recognition; official end of the support of Adobe Flash, etc. etc.

Kit Kat 4.4 (October 2013)Support for 3 new types of sensors (geomagnetic rotation vector, step detector and counter), added step counter feature; decreased battery consumption during audio playing; Android RunTime (ART) and new compiler, experimental in this version, that can be activated in Developers Options (not on all devices); optimized working on devices with limited RAM, …


Android:


Lollipop 5.0-5.1.1 (November 2014)Introduction of Google Fit for physical activity; new Linux 3.10.x. kernel;removal of Dalvik runtime, that is officially replaced by ART; native 64 bit support; Bluetooth 4.1; improvement of graphical performance thanks to OpenGL ES 3.1 support; improvement of camera support thanks to dedicated APIs; added multi-user features on smartphones; …

Marshmallow 6.0 (October 2015)Doze mode, with CPU speed reduction when display is switched off; native support to fingerprint readers; Direct Share for sharing among apps; request of post-install/run-time permissions; USB Type-C support; support to External storage to make it uniform to Internal Storage; MIDI support for music instruments; experimental multi-window feature


Android:


Nougat «N» 7.1.2 (August 2016) – API 25Ability to display multiple apps on-screen at once in a split-screen view; support for inline replies to notifications; OpenJDK-based Java environment; support for the Vulkan graphics rendering API; "seamless" system updates on supported devices; …

Oreo 8.0 (August 2017) – API 26Project Treble, i.e., modular architecture that makes it easier and faster for hardware makers to deliver Android updates; multi-display support

Pie 9.0 (August 2018) – API 28Experimental features (hidden within a menu called Feature Flags) such as automatic Bluetooth enabling while driving; DNS over TLS; Vulkan 1.1 -low-overhead, cross-platform 3D graphics and computing API


Android versions by term

54


Kernel Linux 3.x

Hardware Abstraction Layer (HAL)

❑ Memory management

❑ Process management

❑ Network stack

❑ Standard Linux power management

❑ …

55

Kernel extensions❑ Ashmem: shared memory manager;

reference counting and automatic deallocation by the kernel

❑ IPC binder: low overhead thanks to the usage of Ashmem (rigid access discipline via memory block descriptors)

❑ Advanced power management: exploitation of different energy management policies via WakeLocks

Android:

OS Kernel Layer

It is NOT a real complete Linux OS kernel. It lacks:❑ Native window manager system

❑ Complete support to GNU C library

❑ Complete support to standard Linux utilities


Power Management

and WakeLocks

Manifest example of cross-layering

Android apps (with permission to access Power Manager) can achieve control of energy consumption by enforcing the desired policy:

❑ Always active CPU, also with switched-off display

❑ Prioritary CPU with display that is at least backlit

❑ …

Via WakeLocks: access locks to the features of Power Manager (different types of WakeLock). For instance:

… @Override

protected void onCreate(Bundle savedInstanceState) {

PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);

wl = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK, "DoNotDimScreen"); }

@Override

protected void onPause() { super.onPause(); wl.release(); }


Native libraries for graphics and multimedia

Dalvik VM❑ designed for mobile devices: registry-based (exploiting the ARM

architecture). Instead, how is the traditional JVM organized?

❑ It interprets and runs dex files, obtained via transformation of class files

(30% reduction of necessary instructions and improvement of runtime perf)

❑ optimized support to garbage collection

Android:

Native Libraries and Dalvik VM

Surface Manager + Media Framework

3D Surface3D Surface3D Surface3D Surface

2D Surface2D Surface2D Surface2D Surface

SurfaceSurfaceFlingerFlingerSurfaceSurfaceFlingerFlinger

FrameFrameBufferBufferFrameFrameBufferBuffer

Audio Flinger

Audio Audio FlingerFlinger

App App App App

CameraCamera

Camera

Service

Camera

Service

OpenCOREOpenCOREVorbisVorbis MIDIMIDI

Media Player Service


Media RecorderService


Media Server

CameraCamera

Camera

Service

Camera

Service






CameraCamera

Camera

Service

Camera

Service






Media Server


Activity❑ A single action that one user can accomplish via a window (itcorresponds usually to a single screen)❑ It is the fundamental Androidcomponent

➢ E.g., home activity

Intent❑ Maximum reusability of activity❑ Request to perform an operation (e.g., choice of a phone number)❑ Received by a component that has a compatibile Intent Filter

Service❑ Running in background (no interaction with user, differently from activity)❑ Usable by 1+ components❑ No dedicated process/thread in background

Broadcast Receiver❑ Responds to compatible Intents by executing the associated operations❑ Typically, notify actions (calls, sms transmissions, …)❑ Lifecycle is limited to the response❑Differently from activities and services, multiple receivers can be activated by a single intent

Android:

Application Framework


❑ Package and Activity ManagerManage the lifecycle of Activities and apps, included in Android Packages (APK). Each APK includes a descriptor (manifest), executable dex, and the associated «static» resources (xml, png, …), according to a predefined file structure

❑ Window Manager and View SystemOffer advanced graphics features that can be used directly in apps. View System is based on the View class, and consists of GUI components that interact with user and with event managers (no Java Swing, no AWT)

Applications

❑ Resource Manager and Content

ProviderResource manager for any resource (all files except for code) and shared access to local data (SQLite RDBMS and persistence through files)

❑ Telephony, Notification, and Location Manager

Allow to access functionality for telephony, notification, and positioning

Android: Application Framework


Core Applications

Real and regular apps (same execution model as for apps developed by

third parties and downloaded by users), pre-installed at default over an Android device

➢ Home application (and associated activity): manager app frm which it is possible to launch execution of other apps. Which threading model?

➢ Message management

➢ Client app for email

➢ Contact book

➢ Map management

➢ Web browser: WebKit browser engine

(open-source); used also in Safari and

Google Chrome

Only browser engine (HTML parser +

renderer + JavaScript engine)

Applications

Android: Core Applications


Lifecycle Management of

Android Activities

❑Activity is the component for user

interaction❑It extends the Activity Java class

❑In general, many activities are running

concurrently: the active one

(RUNNING) is only ONE. If visible but

not active, it is PAUSED, otherwise

STOPPED

❑For lifecycle management, it is

possible to redefine callback

methods OnCreate, OnStart,

OnResume,…

❑Activities use resources: an activity

may be deallocated due to resource

shortage → KILLED state

❑Android offers an info container

called Bundle, where to save the

state to be recovered at re-allocation

STOPPED

OnCreate()

OnStart()

OnResume()

RUNNING

a) New activityb) Back button

OnPause()

PAUSED

Activity is no more visible

OnStop()

OnDestroy()

INACTIVE

Activity comesback in foreground

Activity comesback in

foreground

OnRestart()

Resource shortage

INACTIVE

(KILLED)

Activity comesback in foreground

OnRestoreInstanceState(Bundle)

OnSaveInstanceState(Bundle)

Bundle


Conversation Concept:

Android TaskOne App may include several activities:

❑ Independent and disjoint

❑ Associated the one with the other

Activities are different from forms

❑ They should be simple

❑ They should be usable and reusable

→ there is the need to structure activities to

compose a more complex conversation

with user (as for Web pages)

A task models a conversation

❑ It includes an activity stack, also of

different apps: on top the only active

activity in the task

❑ Activity start pushes it on top of the

stack; its closing discards the activity

from the stack

❑ It may be in foreground or in

background

MyFirstProject

it.mypackage

process

MyActivity

App Dialer

Dialer process

Contacts

Dialer

…

MyActivity

Contacts

TASK

root activity

top of the

stack


Intent and Intent Filter

Activation of a component is triggered by an Intent(usually to pass from an activity to the following one)

❑ explicit: component to activate is known at compile time; it needs the Class descriptor of the component

❑ implicit: component to activate is NOT known at compile time; it needs that the following data are specified

➢ action and category: they describe respectively action and type of the component to activate for execution

➢ url: it specifies data to be processed by the activated component

➢ mime type: it specifies the data type usedIntent intent = new Intent(Intent.ACTION_VIEW);

intent.setData(Uri.parse(“http://www.unibo.it”));

Component is selected based on applicable Intent Filters (description of which intents an activity can handle) that are declared in the manifest, according to an algorithm of Intent Resolution

Intent repository on www.openintents.org

http://www.openintents.org/


Intent and Intent Filter

protected void onCreate(Bundle savedInstanceState) {

...

Intent intent = new Intent(); intent.setAction(MY_ACTION);

intent.addCategory(Intent.CATEGORY_ALTERNATIVE);

intent.addCategory(Intent.CATEGORY_BROWSABLE);

Uri uri = Uri.parse("content://it.mypackage/items/");

intent.setData(uri);

intent.setType("vnd.android.cursor.item/vnd.mytype");

startActivity(intent); ... }

<activity android:name="IntentActivity">

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.

LAUNCHER" />

<category android:name="it.mypackage.intent.

category.CAT_NAME" />

<data android:mimeType="vnd.android.cursor.item/

vnd.mytype" />

</intent-filter>

</activity>

Example

of

manifest

file


Threading Model in Android

Each application has a single thread (at default) =>

simple single-threaded model (1 app: 1 thread)

❑ 1 app: 1 system thread “assigned” to the app: multiple activities

❑ Possibility to save the state in info bundle (not very different from

execution model of stateful session beans in J2EE)

❑ Each thread has a Looper for message queue management


Threading Model in Android

Two options: 1) to launch different apps in a single Dalvik VM (single

heavy process); 2) to have a single Dalvik VM (process) dedicated

to each single app

The default is the second option: any app is put in execution into a

separated VM (separated isolated process), also when triggered by

startActivity(intent) or startService(intent)

How is it possible? Which potential issues?

For instance, how to perform response return to the «invoking» activity?

startActivityForResult(Intent, int)

second parameter identifies the call

callback function onActivityResult(int, int, Intent)

If it is crucial to optimize system resource consumption, there is the need

to impose that different apps share the same userID

Android.sharedUserId=“PaoloBellavista” in manifest file

Which potential security issues?


Android Scheduling

1. Foreground

2. Visible

3. Service

4. Background

Process level:

App A

App A

Foreground Thread Group

Background Thread Group

App B

App B

> 90%

< 10%

Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);

67


Asynchronous Techniques

❑ Thread

❑ Executor

❑ HandlerThread

❑ AsyncTask

❑ Service (already partially discussed)

❑ IntentService

❑ AsyncQueryHandler

❑ Loader

68


Android Threads

❑ Act much like usual Java Threads

❑ Cannot work directly on external User Interface objects (throw the Exception CalledFromWrongThreadException: “Only the original thread that created a view hierarchy can touch its views”)

❑ Cannot be stopped by executing destroy() nor stop(). Use instead interrupt() or join() (by case)

❑ As usual, two main ways of having a Thread that executes application code:➢ Providing a new class that extends Thread and

overriding its run() method

➢ Providing a new Thread instance with a Runnable object during its creation.

In both cases, start() method must be explicitly called to actually execute the new Thread

69


Android Handler

❑ Associated with a single thread and that thread's message queue

❑ Bound to the thread/message queue of the thread that has created it

❑ It delivers messages and runnables to that message queue

❑ It executes them as they come out of the message queue

Two main types of usage for a Handler:

➢ To schedule messages and runnables to be executed as some point in the future

➢ To add an action into a queue performed on a different thread

70


Handler Example

71


Android AsyncTask

❑ Created on the UI thread and can be executed only once

❑ Run on a background thread and result is published on the UI thread

❑ The three parameters of an AsyncTask are:➢ Params, the type of the parameters sent to the async task upon

execution

➢ Progress, the type of the progress units published during the background computation

➢ Result, the type of the result of the background computation

❑ Go through 4 steps:➢ onPreExecute(): invoked on the UI thread immediately after the

async task is started

➢ doInBackground(Param ...): invoked on the background thread immediately after onPreExecute() finishes executing

➢ onProgressUpdate(Progress...): invoked on the UI thread after a call to publishProgress(Progress...)

➢ onPostExecute(Result): invoked on the UI thread after background computation finishes

72


AsyncTask Example

73


❑ Violate the single thread model: the Android UI toolkit is not

thread-safe and must always be manipulated on the UI thread

❑ In this piece of code, ImageView is manipulated on a worker

thread, which can cause really weird problems. Tracking down

and fixing such bugs can be difficult and time-consuming

To Summarize: Pay Attention…

74


❑ Classes and methods also tend to make the code more complicated and more difficult to read

❑ It becomes even worse when implementing complex operations that require frequent UI updates


75



76


Example: Developing a Launcher

for Replacing the usual Home

A custom home can be created by:

1. Defining a new Activity

2. Declaring the launcher’s action MAIN in

the Intent Filter

3. Searching installed apps via Package

Manager

4. Selecting the only apps that have an Intent

Filter related to launch

5. Creating a selection View (Button) for each

suitable app

6. Defining the click event: Intent notification

7. Association of the event to the View

As already mentioned, home allows starting any app, serving as a launcher

Android as an open platform – “All Apps are created equal” → it is possible to

customize the system with our own home


// Step 1: definition of a new activity

public class CategoryTestActivity extends Activity {

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

LinearLayout activitiesList;

activitiesList = (LinearLayout)

findViewById(R.id.activitiesList);

// Steps 3 and 4: app search and selection based on IntentFilter

Intent intent = new Intent();

intent.setAction(Intent.ACTION_MAIN);

intent.addCategory(Intent.CATEGORY_LAUNCHER);

PackageManager pkgManager = getPackageManager();

List<ResolveInfo> activities =

pkgManager.queryIntentActivities(intent, 0);

…




…

for (ResolveInfo resolveInfo : activities) {

final ResolveInfo ri = resolveInfo;

Button button = new Button(this); //Step 5: one button per app

button.setText(resolveInfo.loadLabel(pkgManager));

// Step 7: event-view association

button.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

Intent intent = new Intent(); //Step 6: intent launch

ComponentName cn = new ComponentName(ri.

activityInfo.packageName, ri.activityInfo.name);

intent.setComponent(cn);

intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

intent.addFlags(Intent.FLAG_ACTIVITY_MULTIPLE_TASK);

startActivity(intent);}});

activitiesList.addView(button);}}}




<manifest xmlns:android=“...” package="it.mypackage">

<application android:label="@string/app_name">

<activity android:name=".HomeActivity"

android:label="@string/app_name">

<intent-filter> <!– Step 2 -->

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />


HOME"> </category>


DEFAULT"></category>

</intent-filter>

</activity>

</application>

</manifest>




Android Security

in a Single Slide

<manifest xmlns:android="http://schemas.android.com/apk/res/

android“ package="com.google.android.app.myapp" >

<uses-permission id="android.permission.RECEIVE_SMS" />

</manifest>

Typical guidelines for security in Linux

❑ At default any Android app runs in a dedicated Dalvik VM

and within its own separated process. Which UID/GID?

➢ Process and group identifiers are selected from an interval that is

defined system-level: FIRST_APPLICATION_UID, LAST_APPLICATION_UID

❑ Process-level permissions are assigned and controlled

depending on user ID & group ID assigned to

processes. Typically what do you expect?

❑ Finer-grained permissions are assigned (and revocable) even for a

single operation via manifest file


Exercise on Android

To design and develop a simple context-dependentAndroid app (for example, able to play different audio/video files

depending on current user location), by employing the APIs of the Media Framework library (native) and the APIs of the Location Manager (Java-based, application framework level)

Suggestion to use, but free personal choice ☺:

❑ Android Studio and SDK toolshttps://developer.android.com/studio/index.html

It could be the initial starting seed for a possible project activity…

As additional examples of Android usage and project activities, please see alsohttp://lia.disi.unibo.it/Courses/sm1415-info/esercizi.html

https://developer.android.com/studio/index.html

http://lia.disi.unibo.it/Courses/sm1415-info/esercizi.html


Many and Many Available Sources

for Additional InfoMany good (not only good ) books on Android:

❑ E. Hellman, “Android Programming: Pushing the Limits”, Wiley,

Nov. 2013

❑ Z. Mednieks, L. Dornin, “Programming Android: Java Programming

for the New Generation of Mobile Devices”, O’Reilly, Ott. 2012

❑ R. Meier, “Professional Android 4 Application Dev.”, Wrox, 2012

❑ F. Ableson, R. Sen, “Android in Action”, Manning, Feb. 2011

Android SDK has good manuals and how-tos, e.g., description of

available APIs, presentation of examples of apps, …

❑ http://developer.android.com/sdk/index.html

Further info and documents are available at the Android Studio Web site:

❑ https://developer.android.com/studio/index.html

http://developer.android.com/sdk/index.html

https://developer.android.com/studio/index.html


iOS (or iPhoneOS):

a Very Rapid OverviewApproach is very similar to Android from many perspectives and

in terms of realization of a wide support ecosystem, i.e.,

development model + support API:

❑ iOS exploits a variant of the XNU kernel, which is at the basis of

MacOSX

❑ Chain of development tools is similarly based on Xcode

SDK includes APIs at different layers to support:

SDK also includes iPhone Simulator, i.e., a tool to emulate iPhone look&feel

over developer desktop. It is not a real emulator: it runs code that is actually

generated for another target (x86)

SDK requires a Mac OS X Leopard host (or more recent)

➢Events and multi-touch controls

➢Accelerometer

➢Localization (i18n)

➢Camera and media in general (audio

mixing&recording, video playback, several image

file formats, OpenGL ES …)

➢Networking

➢Embedded SQLite database

➢Core Location (GPS, Skyhook WiFi, …)

➢Thread

➢Power management

➢File system

➢Security


iOS (or iPhoneOS):

Rules Rules Rules…

❑ 3.3.1 — Applications may only use Documented APIs in the manner

prescribed by Apple and must not use or call any private APIs.

Applications must be originally written in Objective-C, C, C++, or

JavaScript as executed by the iOS WebKit engine, and only code written in

C, C++, and Objective-C may compile and directly link against the

Documented APIs

❑ 3.3.2 — An Application may not itself install or launch other executable

code by any means, including without limitation through the use of a plug-in

architecture, calling other frameworks, other APIs or otherwise. No

interpreted code may be downloaded or used in an Application except for

code that is interpreted and run by Apple’s Documented APIs and built-in

interpreter(s)

Even the SDK can be downloaded for free but calls for registration to

iPhone Developer Program if developers are willing to release some

software (paying a fee + subject to Apple’s approval)

Apple has not announced any plan for supporting Java over iPhones;

initially some partial support instead for J2ME over iOS


How to Develop in iOS:

First Steps

To start:

❑ http://developer.apple.com/iphone/

❑ Download the iOS SDK, which includes:

➢ Xcode

➢ iPhone emulation tools

➢ Monitoring tools

➢ Interface builder

Please note that apps are subject to Apple’s approval (included in the

signed agreement for SDK download), with the idea of performing

reliability tests and other investigations…

Apps may be rejected if evaluated as of "limited utility"

http://developer.apple.com/iphone/


Alternative Possibilities for

iOS Development

Primary option: exploitation of Xcode and Objective C,

exactly same way as in traditional MacOSX

Alternatively:

❑ Web applications that employ AJAX/Javascripttechnologies; HTML5 set of solutions; possibility to access via Safari

❑ Also (but rare) usage of Java

➢ AlcheMo for iPhone

➢ Xmlvm

➢ Java installation over “unlocked” and “jailbroken” iPhone

By the way, do you know what the terms “unlocking” and “jailbreaking” mean?


Unlocking & Jailbreaking

To be precise, unlocking and jailbreaking identify two different procedures

❑ Unlocking is the process through which a device is made compatible with telco networks for which it was not specifically licensed (overcoming the locking with a given dedicated telco operator)

❑ Jailbreaking is the process through which a developer exits her own “jail” in UNIX-like OS and/or breaks the imposed system of Digital Right Management (DRM). It is a specific form of growth of execution privilege

❑ In iOS, it allows a user to execute arbitrary code and apps, by bypassing the regular mechanism of distribution of Apple code (based on iTunes App Store and iTunes Application)

To enjoy yourself ☺ with experimentation, tools such as:

➢ PwnageTool, QuickPwn, Yellowsn0w http://blog.iphone-dev.org/

➢ Pusher - http://ripdev.com/pusher/

➢ Linux on iPhone - http://www.iphonelinux.org/index.php/Main_Page

➢ ZIPhone - http://www.ziphone.org/

http://blog.iphone-dev.org/

http://ripdev.com/pusher/

http://www.iphonelinux.org/index.php/Main_Page

http://www.ziphone.org/


Cross platform based on HTML5

89


Cross platform based on HTML5

90


Cross platform - Xamarin

91


Cross platform - Xamarin

92


iOS:

AJAX & JavaScript

AJAX (“maybe” Asynchronous JavaScript and XML): set of correlated

techniques for the development of highly interactive Web applications (rich Internet applications)

❑ Possibility of asynchronous data retrieval in background, with no interference on behavior and visualization of current page

➢ To some extent and from some perspectives, applets as AJAX precursors

❑ With Safari browser, possibility of highly interactive and “native looking” Web applications

Question: which pros in using Web applications in place of native apps?

❑ AJAX plugin per Eclipse (available also as a standalone version): http://www.aptana.com/

http://www.aptana.com/


Also proposals that succeeded in terms of standardization.

For example:

❑ Canvas element as third-party JavaScript extension that allows dynamic rendering of bitmap images

➢ Introduced by Apple for usage within Webkit component of MacOSX (forming the basis of Safari browser), then adopted by Mozilla and Firefox

➢ Standardized by WHATWG (see last slide) for the new specification proposals towards HTML5

➢ Canvas is a “drawable” area defined in the HTML code, with attributes for height and size. JavaScript code can use a wide set of drawing functions, by allowing to use dynamically generated graphics (drawings, animations, image compositions/elaborations, …)

➢ In competition with Macromedia Flash/FlashLite. For instance, see these two examples:

▪ http://www.damonkohler.com/2008/12/javascript-painting-with-canvas.html

▪ http://www.benjoffe.com/code/demos/canvascape/

iOS:

AJAX & JavaScript

http://www.damonkohler.com/2008/12/javascript-painting-with-canvas.html

http://www.benjoffe.com/code/demos/canvascape/


Web Applications:

HTML5 in a Single SlideAgain, the fundamental question is pros&cons of

Web applications vs. native apps

HTML5❑ Nothing of groundbreaking originality, it uses the traditional classical

model of Web applications with rich interactivity

❑ HTML5 = HTML + CSS + JavaScript

➢ W3C finalized it (at the end :-)!) in October 2014

By delving into finer details:

❑ New tags for AJAX and DHTML

❑ New tags for embedded management of audio and video files (e.g., <video> tag)

➢ To what extent are they currently supported? In a completely standard way?

❑ Better management of document structure

For example, see http://w3c.github.io/html/ (draft version 5.2 – April 18, 2017)

➢ http://slides.html5rocks.com/

http://w3c.github.io/html/

http://slides.html5rocks.com/

Documents

04 Development and Runtime Platforms: Overview, J2ME, iOS ...lia.disi.unibo.it/Courses/sm1819-info/lucidi/04-Platforms(1x).pdf · Development/Runtime Platforms –Mobile Systems M