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In CAPITALS

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Muhammad Rizwan Asghar

March 18, 2020

ANDROID APP MODEL

Lecture 8

COMPSCI 702

Security for Smart-Devices

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AN INSTANCE OF DALVIK VM PER APK

Init

Linux Kernel

Zygote

DalvikVM

APK2

DalvikVM

APK3

DalvikVM

APK1

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ANDROID APPLICATION PACKAGE

(APK)

APK is a packing format

Parts of an APK

– Classes.dex (Dalvik executable)

Android app components

– Application can contain native code

C/C++ shared libraries linked dynamically

– Resources and assets

E.g., images, string values, layout definitions, and

raw data

– META-INF

It includes the certificate and signature information

– Application manifest

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SIGNING YOUR APP

Android requires that all apps to be digitally

signed with a certificate

Android apps often use self-signed certificates

Android uses this certificate to identify the

developer of an app

Android follows the same origin policy– Android uses the same signing key pair to make sure that

updates are coming from the same developer

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APPLICATION MANIFEST

An XML format

Declares application metadata and components– Names, intent filters, and permissions

Main elements– Package information

Package name and version

– App information

Launcher icon

– Activity component

– …

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APPLICATION MANIFEST: A SAMPLE

<?xml version="1.0" encoding="utf-8"?>

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

android:versionCode="1"

android:versionName="1.0"

package="com.example.compsci702.helloworld"

platformBuildVersionCode="23"

platformBuildVersionName="6.0-2438415">

<uses-sdk android:minSdkVersion="15"

android:targetSdkVersion="23" />

<application android:theme="@style/AppTheme"

android:label="@string/app_name"

android:icon="@mipmap/ic_launcher"

android:allowBackup="true"

android:supportsRtl="true">

<activity android:theme="@style/AppTheme_NoActionBar"

android:label="@string/app_name"

android:name="com.example. compsci702.helloworld.MainActivity">

<intent-filter>

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

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

</intent-filter>

</activity>

</application>

</manifest>

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ANDROID APP COMPONENTS

Android app is a combination of loosely

coupled components

Each component can offer multiple entry points

– Activity

User interface

– Service

Background services

– Content provider

Database

– Broadcast receiver

Mailbox for broadcasted messages

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INTENT

Intents are named events

Represents the intent to do something

Examples– Launching an activity

– Starting a service or

– Broadcasting a message

Its payload and attributes describe the intended

action

It can be sent and received by an application

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INTENT TYPES

Explicit– Sets the target component name

– E.g., “com.example.app.MainActivity”

Implicit– Provides information including action, data, and type

– Resolved at runtime by the Package Manager

– Android framework will find a suitable receiver for this intent

– Example

Action=intent.ACTION_VIEW;

Data=www.youtube.com

It will open the app that can show youtube

It could be the default web browser or youtube app

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WHERE IS PACKAGE MANAGER?

Linux Kerne lDisplay Driver Camera Driver Bluetooth Driver

Shared Memory Driver Binder (IPC) Driver

Power ManagementUSB Driver Keypad Driver WiFi Driver

Audio Drivers

Appl icat ionsHome Dialer

Contacts

SMS/MMS

Email Calendar Media Player Albums

Appl icat ion Framework

IM Browser Camera

Clock

Calculator

…Voice Dial

Alarm

Android RuntimeCore Libraries

Dalvik Virtual Machine

View SystemContent Providers

Resource Manager …

Libc

Notification Manager

Location Manager

FreeType

SGL SSL

SQLite

WebKitOpenGL|ES

And r o id RuntimeCore Libraries

DalvikVirtual Machine

Libraries

FreeType

Surface Manager

OpenGL|ES

Media Framework

Activity Manager

Package Manager

Window Manager

Telephony Manager

Source: Android Anatomy and Physiology, Patrick Brady

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ACTIVITY

A main building block of Android GUI

applications

Activity is like a website– Multiple activities ~ multiple web pages

– Main activity ~ homepage

– Moving from one activity to another ~ navigation

E.g., in Contacts app, choosing to compose a message to

a contact by launching the Messaging app

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ACTIVITY LIFECYCLE

System calls component

as its state changes due

to user actions

If another activity is

started, the on-going

activity is paused

App process may be killed

A stopped activity may be

destroyed

Source: android.com

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ACTIVITY MANAGER

Activity Manager is responsible for creating, destroying, and

managing activities

When the user starts an application for the first time, the Activity

Manager will create its activity and put it onto the screen

Later, when the user switches screens, the Activity Manager will

move that previous activity to a holding place

This way, if the user wants to go back to an older activity, it can be

started more quickly

Older activities that the user has not used in a while will be

destroyed in order to free more space for the currently active one

This mechanism is designed to help improve the speed

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TO BE CONTINUED

See the next lecture

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15

Questions?

Thanks for your attention!