02 android architecture · Luca Bedogni -Programming with Android–System Architecture 6 Android...

Programming with Android: System Architecture

Luca BedogniDipartimento di Scienze dell’Informazione

Università di Bologna

Luca Bedogni - Programming with Android – System Architecture 2

Outline

Android Components: Content Providers

Android Components: Services

Android Components: Intents

Android Components: Activities

Android Java Virtual Machine

Android Architecture: An Overview

Android Application Distribution and Markets


Android … What?

vAndroid is a Linux-based platform for mobile devices …

§ Operating System§ Middleware§ Applications§ Software Development Kit (SDK)

v Which kind of mobile devices … (examples)

SMARTPHONES TABLETS EREADERS ANDROID TV GOOGLE GLASSES

?


Android … What?

SMARTPHONES TABLETS EREADERS ANDROID TV GOOGLE GLASSES

?SMART FRIDGE

ANDROID MICROWAVE


Android … When?

ØGoogle buys Android from the Android Inch

ØOpen Handset Alliance (OHA) created for open standards for mobile devices. Partners of OHA: Google, Motorola, Samsung, Vodafone, T-Mobile, etc

ØAndroid 1.0 Released

ØThe first Android smartphone: G1 HTC-Dream

ØAndroid 1.1 ReleasedØAndroid 1.5 (CupCake) Released

2005

2006

2007

2008

2009

Time


Android … When?

ØAndroid 1.6 (Donut) Released

ØAndroid 2.0 (Eclair) Released

ØAndroid 2.2 (Froyo) Released

ØAndroid 2.3 (Gingerbread) Released

ØAndroid 3.0 (Honeycomb) Released(First version for devices with larger screens such as tablets)

ØAndroid 4.0 (Ice-Cream Sandwich) Released. (It merges the 3.x tab centric design and the v2.x phone based design into a single version.)

2008

2009

2010

2011

2012

Time


Android … When?

ØAndroid 4.4 (Kitkat) Released

ØWireless printing capabilityØAbility for applications to use "immersive mode”ØPerformance optimization ØNew experimental runtime virtual machine, ART…

API Level 19 (Android 4.4):

Ø Support to new embedded sensors (e.g. STEP_DETECTOR)

Ø Adaptive video playback functionalitiesØ Read and write SMS and MMS messages

(managing default text messaging client)

2012

2013

Time

ANDROID 5.0

2014


Android … market share


Android … heterogeneityht

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Android … heterogeneity


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2015

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http://developer.android.com/about/dashboards/index.html


Android … When?

http://www.appbrain.com/stats/android-market-app-categories

ANDROID APP CATEGORIES

http://www.onlinemarketing-trends.com/2011/07/android-marketplace-top-5-statistics.html

ANDROID APP PRICE


The Android Architecture



Built on top of Linux kernelAdvantages:

Ø Portability (i.e. easy to compile on different hardware architectures)

Ø Security (e.g. secure multi-process environment)

Ø Power Management

Ø ART relies on the kernel for threads and memory management

Ø Manufacturers build on top of a reliable kernel

Luca Bedogni - Programming with Android – System Architecture

Kernel Security

vUser based permission modelvProcesses are isolatedvInter-process communication (IPC)vResources are protected from other processesvEach application has its own User ID (UID)vSandboxvVerified boot

23



HAL

Advantages:

Ø Shadows the real device

Ø Manages different devices of the same type

Ø Standard interfaces to expose lower level capabilities to higher level APIs


HAL

Ø Standard interface that manufacturers have to implement – Android is agnostic about lower level driver implementations

Ø Application developers rely on common APIsØ Depending on the hardware, appropriate libraries are loaded



Native Libraries (C/C++ code)

ØGraphics (Surface Manager)

ØMultimedia (Media Framework)

ØDatabase DBMS (SQLite)

ØFont Management (FreeType)

Ø WebKit

ØC libraries (Bionic)

Ø….


Android NDK

ØEnables C/C++ coding

ØUseful if you want to interact/extend with some native librariesØ PerformanceØ Reuse your C/C++ libraries

ØJAVA APIs are provided for most used libraries

ØNDK can be installed as an Android Studio plugin

public class myNDKActivity extends Activity {public native void doNothing():

}



APIs (Core Components of Android)

ØActivity Manager

ØPacket Manager

ØTelephony Manager

ØLocation Manager

ØContents Provider

ØNotification Manager

Ø….


Java APIs

ØView SystemØ Through which you build the APP UI

ØResource ManagerØ Through which you handle resources

ØNotification ManagerØ Through which you can access to different kind of notifications

ØActivity ManagerØ Which handles the Activity lifecycle

ØContent ProvidersØ To share data among APPs



Applications(Written in Java code)

ØAndroid Play Store

ØEntertainment

ØProductivity

ØPersonalization

ØEducation

ØGeo-communication

Ø….



ART (VM)

ØNovel Java Virtual Machine implementation (not using the Oracle JVM)

ØOptimized for memory-constrained devices

ØFaster than Oracle JVM

ØART optional from 4.4, mandatory from 5.0


ART

ØStarting from Android 5.0, ART is used instead of Dalvik

ØDesigned to run multiple VM on low end devices

ØRuns DEX bytecode

ØAhead-of-time (AOT) and Just-in-time (JIT) compilationØ AOT: At install time, ART compiles APPs using an on-device tool called dex2oatØ JIT: code profiling

ØOptimized Garbage collection


Android Applications Design

ØGUI Definition

ØEvents Management

ØApplication Data Management

ØBackground Operations

ØUser Notifications

APPLICATION DESIGN:


Android Applications Design

ØActivities & Fragments

Ø Intents

ØServices

ØContent Providers

Ø Broadcast Receivers

APPLICATION COMPONENTS



ØAn Activity corresponds to a single screen of the Application.

ØAn Application can be composed of multiples screens (Activities).

ØThe Home Activity is shown when the user launches an application.

ØDifferent activities can exhange information one with each other.

Hello World!

Android HelloWorld

Button1



ØEach activity is composed by a list of graphics components.ØSome of these components (also called Views) can interact

with the user by handling events (e.g. Buttons). ØTwo ways to build the graphic interface:

Example:

Button button=new Button (this);TextView text= new TextView();text.setText(“Hello world”);

PROGRAMMATIC APPROACH



ØEach activity is composed by a list of graphics components.ØSome of these components (also called Views) can interact

with the user by handling events (e.g. Buttons). ØTwo ways to build the graphic interface:

DECLARATIVE APPROACH

Example:

< TextView android.text=@string/hello” android:textcolor=@color/blue android:layout_width=“fill_parent” android:layout_height=“wrap_content” />< Button android.id=“@+id/Button01” android:textcolor=“@color/blue”android:layout_width=“fill_parent” android:layout_height=“wrap_content” />


- Build the application layout through XML files (like HTML)

- Define two different XML layoutsfor two different devices

- At runtime, Android detects the current device configuration and loads the appropriate resources for the application

- No need to recompile!- Just add a new XML file if you

need to support a new device

EXAMPLE

Device 1HIGH screen pixel density

Device 2LOW screen pixel density

XML Layout FileDevice 1

XML Layout FileDevice 2

Java App Code




ØAndroid applications typically use both the approaches!

DECLARATIVE APPROACH

PROGRAMMATIC APPROACH

Define the Application layouts and resources used by the Application (e.g. labels).

Manages the events, and handles the interaction with the user.

XML Code

Java Code



ØViews can generate events (caused by human interactions) that must be managed by the Android-developer.

public void onClick(View arg0) {if (arg0 == Button) {

// Manage Button events}

}

ESEMPIO

Butto

n

Text

Edit



ØThe Activity Manager is responsible for creating, destroying, managing activities.

ØActivities can be on different states: starting, running, stopped, destroyed, paused.

ØOnly one activity can be on the runningstate at a time.

ØActivities are organized on a stack, and have an event-driven life cycle (details later …)



ØMain difference between Android-programming and Java (Oracle) -programming:

ØMobile devices have constrained resource capabilities!

ØActivity lifetime depends on users’ choice (i.e. change of visibility) as well as on system contraints (i.e. memory shortage).

ØDeveloper must implement lifecycle methods to account for state changes of each Activity …



public class MyApp extends Activity {

public void onCreate() { ... }public void onPause() { ... }public void onStop() { ... }public void onDestroy(){ ... }….

}

Called when the Activityis created the first time.

Called when the Activityis partially visible.

Called when the Activityis no longer visible.

Called when the Activityis dismissed.



Ø Intents: asynchronous messages to activate core Android components (e.g. Activities).

ØExplicit Intent à The component (e.g. Activity1) specifies the destination of the intent (e.g. Activity 2).

LOGIN

PASSWORD

Login

luca

**********

Welcome Luca!

Login Intent

Activ

ity1

Activ

ity2



Ø Intents: asynchronous messages to activate core Android components (e.g. Activities).

Ø Implicit Intent à The component (e.g. Activity1) specifies the type of the intent (e.g. “View a video”).

View

Implicit Intent

Activ

ity1

Activ

ity2

Activ

ity2

Multiple choicesmight be available

to the user! } Intent-Filters


Android Components: Services

ØServices: like Activities, but run in background and do not provide an user interface.

ØUsed for non-interactive tasks (e.g. networking).Ø Service life-time composed of 3 states:

Starting Destroyed

Running

(on background)

onCreate()onStart() onDestroy()


Android Components: Content Providers

ØEach Android application has its own private set of data (managed through files or through SQLite database).

ØContent Providers: Standard interface to access and share data among different applications.

DB

APPinsert()

update()

delete()

query()

ContentProvider

e.g. Photo Gallery


Android Components: Broadcast Receivers

ØPublish/Subscribeparadigm

ØBroadcast Receivers: An application can be signaled of external events.

ØNotification types: Call incoming, SMS delivery, Wifi network detected, etc


Android Components: Broadcast Receivers

class WifiReceiver extends BroadcastReceiver {public void onReceive(Context c, Intent intent) {

String s = new StringBuilder();wifiList = mainWifi.getScanResults();for(int i = 0; i < wifiList.size(); i++){

s.append(new Integer(i+1).toString() + ".");s.append((wifiList.get(i)).toString());s.append("\\n");

}mainText.setText(sb);

}}

BROADCAST RECEIVER example


Android Components: System API

ØUsing the components described so far, Android applications can then leverage the system API …

Ø Telephony Manager data access (call, SMS, etc)Ø Sensor management (GPS, accelerometer, etc)Ø Network connectivity (Wifi, bluetooth, NFC, etc)Ø Web surfing (HTTP client, WebView, etc)Ø Storage management (files, SQLite db, etc)Ø ….

SOME EXAMPLEs …


Android Components: Google API

Ø… or easily interface with other Google services:


ØEach Android application iscontained on a single APK file.

Ø Java Byte-code

Ø Resources (e.g. images. videos, XML layout files)

ØLibraries (optimal native C/C++ code)

APKFILE

XMLFiles

C

Android Application Distribution


Android Application Distribution

ØEach application must be signed through a key before being distributed.

ØApplications can be distributedvia Web or via Stores.

ØAndroid Play Store: application store run by Google … but several other application stores are available (they are just normal applications).


Android Application Security

ØAndroid applications run with a distinct system identity (Linux user ID and group ID), in an isolated way.

ØApplications must explicitly share resources and data. They do this by declaring the permissions they need for additional capabilities. ØApplications statically declare the permissions they require.ØUser must give his/her consensus during the installation.ØEverything changes starting from 6.0

<uses-permission android:name=“android.permission.ACCESS_FINE_LOCATION" />

<uses-permission android:name=“android.permission.INTERNET" />

ANDROIDMANIFEST.XML


Permissions from 6.0

Ø Android Marshmallow (6.0) introduces runtime permissionsØ Permissions are not requested at install-time, but when they are used

Ø Bad behavior: request everything on the first screen of the first launch of the app

Ø Good behavior: request permission only when neededØAPP should work (with limited functions) even if some

permissions are not granted

02 android architecture · Luca Bedogni -Programming with Android–System Architecture 6 Android...

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