Download Introduction to android

ANDROID
PROGRAMMING INTRODUCTION
Roberto Beraldi
Web resources (android)
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Code
https://developer.android.com/guide/index.html
http://www.vogella.com/tutorials/android.html
http://www.techotopia.com/index.php/Android_4_App_Develop
ment_Essentials
http://www.html.it/guide/guida-android/
https://github.com/aporter/coursera-android
Book and articles
https://androidgroup.googlecode.com/files/Unlocking%20Andro
id.pdf
http://anatomyofandroid.com/
http://css.csail.mit.edu/6.858/2015/readings/android.pdf
Blog of developers
http://stackoverflow.com/
Some fact about Android
• Android, Inc. was founded in Palo Alto, California in
October 2003
• In July 2005, Google acquired Android Inc.
• At Google, the team led by Andy Rubin developed a
mobile device platform powered by the Linux kernel
• Android is built on top of more than 100 open projects,
including Linux kernel
Some fact about Android
• Each application is associated to a Linux user (UID and
GUID) and runs inside a dedicated process
• Use a quite efficient and secure IPC mechanism (Binder)
• To facilitate resource access from isolated applications,
android exploits a permission-based security mechanism
• Each application needs permissions to access system resources
• A permission has a protection level and belongs to a group
• NormalDangerousSignedSystemOrSigned
• Permissions are granted at application installation time
• (at run time 6+)
Support libraries
• As new features are added (e.g., toolbar, actionbar,
fragments,…) support libraries are developed, so that
such features are also available to older android versions
• v4 support, v7 appcompat,etc.. (see documentation)
• Android API are very dynamic, so it can happen that some
method or widget are deprecated (always take a look at
the official documentation)
• Support for multiple languages
• For example:
• Symbolic name given to a string in the code
• Different values according to the nationality of the smartphone
• Support for different versions and screen resolutions
Google play services
• The Google Play services APK
contains the individual Google
services and runs as a background
service in the Android OS.
• The Google Play services APK is
delivered through the Google Play
Store, so updates to the services are
not dependent on carrier or OEM
system image updates.
Accessing Google Play Services
Android architecture
Android architecture (kernel)
The kernel provides preemptive multitasking ,low level core system services, like
Hardware Drivers
Security Settings
Network Stack
Power Management
…
Android architecture, interacting with OS
• The ADB tool (see SDK) allows to interact with the linux
OS via a shell
USB driver
ADB Client
Some example (processes)
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shell@w55n:/ $ ps | more
ps | more
USER PID PPID VSIZE RSS WCHAN PC
NAME
root
1 0 820 680 ffffffff 00000000 S /init
root
2 0 0
0 ffffffff 00000000 S kthreadd
root
3 2 0
0 ffffffff 00000000 S ksoftirqd/0
root
6 2 0
0 ffffffff 00000000 D kworker/u:0
root
7 2 0
0 ffffffff 00000000 D kworker/u:0H
root
8 2 0
0 ffffffff 00000000 S migration/0
root
13 2 0
0 ffffffff 00000000 S khelper
root
14 2 0
0 ffffffff 00000000 S netns
root
18 2 0
0 ffffffff 00000000 S modem_notifier
root
19 2 0
0 ffffffff 00000000 S smd_channel_clo
root
20 2 0
0 ffffffff 00000000 S smsm_cb_wq
root
21 2 0
0 ffffffff 00000000 S kworker/u:1
root
22 2 0
0 ffffffff 00000000 S rpm-smd
root
23 2 0
0 ffffffff 00000000 S kworker/u:1H
root
24 2 0
0 ffffffff 00000000 S mpm
root
25 2 0
0 ffffffff 00000000 S irq/47-cpr
root
55 2 0
0 ffffffff 00000000 S sync_supers
root
56 2 0
0 ffffffff 00000000 S bdi-default
root
57 2 0
0 ffffffff 00000000 S kblockd
root
58 2 0
0 ffffffff 00000000 S system
root
61 2 0
0 ffffffff 00000000 S irq/282-msm_iom
root
62 2 0
0 ffffffff 00000000 S irq/282-msm_iom
Example
• adb pull <f1><f2>
• adb push <f2><f1>
• adb backup
• adb restore <file>
• see adb help for more explanation
Quick guide to adb
• http://code.tutsplus.com/tutorials/android-adb-quick-guide-
-mobile-12456
Android architecture: Dalvik VM
• Designed for:
• Slow CPU
• Little RAM
• 64Mb total, ~10Mb available at runtime
• No swap space
• Limited battery life
• Use registers not stack (like the JVM does)
• It acts as a sandbox: each application runs inside a DVM
• Just In Time compilation
• Translate bytecode to native code just before its execution
• .dex format has footprint 50% smaller
• Replaced in Android 5.0 with Android Run Time (ART)
• Whole app compiled at installation time
See: https://source.android.com/devices/tech/dalvik/index.html
Core libraries
• Core Java classes
• android.*
• java.*, javax.*
• junit.*
• org.apache.*, org.json.*, org.xml.*
• Some of them are wrappers of ‘native libraries’
Native SW libraries (C/C++)
Surface Manager:
Rendering of Views
2D graphics
Open GL ES
2D and 3D graphics
For Embedded systems
Media Framework:
Manage different codec, e.g.
mp3,H.264,MPEG4,etc.
Rendering of
Font types
In process DB
Web engine
(Bionic)C standard library
Java Network Interface (JNI)
• Native libraries can be called from java code
• Java libraries wraps native code
• Developers can write native code (NDK)
• Critical portion of the application (assembly)
• Legacy software
Android architecture: application
framework
Application framework:
Set of services in the
form of managers.
Android frameworks (not complete list)
• Package Manager – The system by which applications are able to find out information about
other applications currently installed on the device.
• Telephony Manager – Provides information to the application about the telephony services
available on the device such as status and subscriber information.
• Location Manager – Provides access to the location services allowing an application to
receive updates about location changes.
• Activity Manager – Controls all aspects of the application lifecycle and activity stack.
• View System – An extensible set of views used to create application user interfaces.
• Content Providers – Allows applications to publish and share data with other applications.
• Resource Manager – Provides access to non-code embedded resources such as strings,
color settings and user interface layouts.
• Notifications Manager – Allows applications to display alerts and notifications to the user.
Android architecture: app layer
Application layer
Security
• Security goals
• Protect sensible data of users, like contact and e-mail
• Protect system resources
• Protect an application from other applications
• Security mechanisms
• Signed Boot Image
• Native mechanisms, at kernel level
• Sandboxing, each application runs inside a sandbox
• Limited access to system resources. Resources restricted via permissions
• Secure IPC
• Application signature via a certificate
• Application-defined and user-granted permissions
Sandbox and permission
Sandbox: Linux UID=1234
Application: UID 1234
DVM
Resources
<uses-permission> ….
android.permission.CAMERA
camera
http://source.android.com/devices/tech/security/#the-applicationsandbox
Sandbox and permission
• Sandbox provides access to a limited number of system
resources
• The access to a resosource is restricted using a
permission
• User should declare the use of the permission in the
manifest file and grant (all) permissions at installation time
• Starting from Android 6.0 this is no longer true
• Sandboxing prevents one app from being able to read
data or modify the code of other apps installed on the
system.
Sandbox and permission
• Different applications can run in the same
process.
• For this approach, one first must sign those
applications using the same private key and then
must assign to them the same Linux user ID
using the manifest file, by defining the manifest
attribute android:sharedUserId with the same
value/name.
Sandobox and permission
Sandbox: Linux UID=1234
Application: UID 1234
Resource
DVM
camera
Application: UID 1234
DVM
Defining a permission
Protection Level of a permission
• Normal
• The default value. A lower-risk permission that the system
automatically grants without asking for the user's explicit approval
• Dangerous
• A higher-risk permission that would give a requesting application
access to private user data. User has to accept the requesting
permission (so that the system will grant it)
• Signature
• A permission that the system grants only if the requesting
application is signed with the same certificate as the application
that declared the permission
Characteristics of android applications
• User interaction
• touch screen based UI interface
• Variable screen size
• From low, medium, high (smart TV)
• Resource
• usage is an issue
• …but..
• Sensors
• Position, orientation, magnetic field, light sensor, ..
• Portable
• Context-awareness based applications (what’s around me, where
are my friends, …)
Bird’s eye view to application architecture
User Interface
Computation
Data
• Activity
• Fragment
UI runs in a thread
Main thread  it should respond fast
 responsiveness
• Service
• Broadcast receiver
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Preference
File
SQLite
Network
Content provider
• Separate thread
• Need mechanism to interact with UI
• Implements the “business logic”
• Many ways to store data
What an application is composed of?
What an application is composed of?
• Software components
• Activity
• Fragment
• Service
• Broadcast receiver
• Content provider
• Intent
• Resources
• Pictures, video, audio file, etc.
• Accessed via an ID
• Accessed via a manager.
Android applications
• Every application runs in its own linux process (receivers
its own User ID)
• A process is created when a component of the application
needs to be run
• An unusual feature of Android is that an application
process’s lifetime is not directly controlled by the
application (more on this soon)
• For example, if the application is temporary not visible the system
may decide to kill the process
Questions?