ANDROID PROGRAMMING - INTRODUCTION. Roberto Beraldi

Transcription

1 ANDROID PROGRAMMING - INTRODUCTION Roberto Beraldi

2 Web resources (android) Code ment_essentials Book and articles id.pdf Blog of developers

3 Smartphone hw architecture A system-on-chip architecture with three primary components: An application processor executing the end-user s application software with assistance from a middleware and operating system (i.e., Android, IOs) A modem or baseband processor with its own operating system components responding to the baseband radio activities A number of peripheral devices for interacting with the end-user

4 Smartphone hw architecture source:

5 Role of application processor Application processor executes the user applications and the related OS services. Applications include audio/video codec and players, games, image processing, speech processing, internet browsing, text editing, etc. Application processor takes help from graphics accelerators as and when needed Most handheld applications are graphics-intensive Smartphones come with reasonably large amount of storage in the form of volatile SDRAM (1-2 GB) as well as non-volatile compact storage (10+ GB)

6 Role of modem processor Reception: The receiver hardware (part of the modem) senses incoming signals and generates interrupts for the radio interface logic of the operating system The radio interface and the operating system software run on a baseband or modem processor Once the reception begins (after a physical layer handshake), the incoming audio, video, and other data are processed by the modem processor The radio OS components talk to the peripheral device drivers to present the incoming data to the user through appropriate devices (display, speaker, etc.)

7 Role of modem processor Transmission: The data to be transmitted are collected by the radio OS components from memory regions populated by the device drivers. For example, audio data captured by the microphone driver or an image or a video captured by the camera or a position information captured by the GPS device A transmission is initiated by the radio interface logic through the modem transmitter hardware The subscriber identification module (SIM) plays an important role in reception and transmission For example it sends the user s authentication key

8 Specific hardware issue Overall, mobile device s hw architecture is similar to desktop one, with some specific difference. In particular System on Chip (SoC) All the hw components are integrated (GPU,Wi-fi,etc) Multicore with cores that can run at different speed, cores activated on demand Rich set of sensors Implemented as IC Mainly RISC architecture (ARM is predominant) One instruction at each clock cycle

9 Example of CPU Qualcom Snapdragon + GPU (Adreno) Different families with different cores (2,4) Nvidia 4i,K1 Intel First 64 bits CPU Mediatek 8 cores Samsung HiSilicon P8

10 HW: Sensors Most devices have built-in sensors that measure motion, orientation, and various environmental conditions. The Android platform supports three broad categories of sensors: Motion sensors. These sensors measure acceleration forces and rotational forces along three axes. This category includes accelerometers, gravity sensors, gyroscopes, and rotational vector sensors. Environmental sensors. These sensors measure various environmental parameters, such as ambient air temperature and pressure, illumination, and humidity. This category includes barometers, photometers, and thermometers. Position sensors. These sensors measure the physical position of a device. This category includes orientation sensors and magnetometers.

11 GPS Based on triangolaritazion 24+3 satellites Circular orbits on 6 circular planes at about 20 Km from the ground The receiver computes the distance from the satellites using synchronized clocks Computing the distance requires to know the delay (about 0,007 s) and start time of the received signal Satellite clocks are atomic clocks, while gps receiver clocks are not, but their values are adjusted when the intersection of the spheres is not unique

12 HW location Other location providers are based on cell-id and wi-fi Android uses these methods together (GPS, cell tower, Wi-Fi) to get an idea of where the device is, and make that available to apps via a "Location Services" API.

13 Communications LTE 4G Up to 326,4 Mbit/s dowload Up to 86,4 Mbit/s upload Wi-fi (with an Access Point) a (54 mbps),802.b (11), g (54),802.11n (300) Wi-fi Direct (p2p) Same standard as wi-fi Bluetooth Latest version 4.1(24Mbps) Make device discoverable...search for the device...enter passcode Set-up times about 6 s IEEE NFC

14 Communication: NFC Active device (reader): generate a magnetic field The reader emits a small electric current which creates a magnetic field that in turn bridges the physical space between the devices. Passive device: react to the field emitting data Like RFID NFC works in the 13.56MHz radiofrequency spectrum using less than 15mA of power to communicate data over distances that are usually far less than 10 cm. Tags typically store between 96 and 512 bytes of data and transfer data using at speeds of 106Kb/s, 212Kb/s or 424Kb/s

15 Communication: NFC NFC Card emulation mode: enables NFC-enabled devices such as smartphones to act like smart cards, allowing users to perform transactions such as payment or ticketing. NFC Reader/writer mode: enables NFC-enabled devices to read information stored on inexpensive NFC tags embedded in labels or smart posters. A tag contains a small amount of non-volatile memory (store text, web address, , vcard, Trigger, e..g. turn on wifi and lunch this app) NFC peer-to-peer mode: enables two NFC-enabled devices to communicate with each other to exchange information in an ad hoc fashion. Applications may use higher-layer, e.g., SSL to establish a secure channel For android see:

16 Typical usage contactless payments, marketing and advertising, security and access control, product identification, location identification, mobile phone task launcher apps.

17 Touch screen technologies Resistive touch screen Capacitive touch screen ( used in modern smartphones) Single touch / multi-touch (pointers)

18 Touch screen: gesture

19 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 To increase security, each application runs with a distinct system identity (Linux UID and GID) Application are isolated from each other Use a quite efficient IPC mechanism To facilitate resource access from isolated application, android exploit a permission-based security mechanism Each application needs permissions to access system resources Permissions are granted at application installation time There are 130 resources (android 4.2)

20 Global market Source: global-market-share-january-2015-increase-android/

21 Android versioning See also:

22 Android screen sizes

23 Some android feature As new features were added (e.g., toolbar, actionbar, fragments, ) support libraries were developed, so that such features were also available to older versions 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 of multiple languages For example: Symbolic name given to a string in the code Different values according to the nationality of the smartphone

24 Android architecture

25 Android architecture (kernel) The kernel provides preemptive multitasking,low level core system services, like Hardware Abstraction Hardware Drivers Security Settings Support for Shared Libraries Network Stack

26 Android architecture (kernel) Android-specific components Binder IPC Android shared memory Power management Alarm driver Kernel debugger & Logger

27 Android architecture, interacting with OS The ADB tool (see SDK) allows to interact with the linux OS via a shell USB driver ADB Client ADB Server Developer option s debug USB enabled RSA key sent to the device must be acknowledged

28 Some example (see file systems) C:\Users\roberto\android-sdks\platform-tools>adb shell $ df df Filesystem Size Used Free Blksize /dev M K M 4096 /sys/fs/cgroup M 12.00K M 4096 /mnt/asec M 0.00K M 4096 /mnt/obb M 0.00K M 4096 /system 1.44G 1.34G M 4096 /data 1.50G M M 4096 /persist 31.46M 4.02M 27.43M 4096 /cache M 4.04M M 4096 /persist-lg 7.83M 4.14M 3.70M 4096 /mpt 31.46M 11.95M 19.51M 4096 /sns 7.83M 4.02M 3.82M 4096 /firmware 63.95M 33.22M 30.73M /cust 49.18M 5.84M 43.33M 4096 /mnt/shell/emulated 1.50G M M 4096

29 Example adb pull <f1><f2> adb push <f2><f1> adb backup adb restore <file> see adb help for more explanation

30 Some example (processes) $ ps more ps more USER PID PPID VSIZE RSS WCHAN PC NAME root ffffffff S /init root ffffffff S kthreadd root ffffffff S ksoftirqd/0 root ffffffff D kworker/u:0 root ffffffff D kworker/u:0h root ffffffff S migration/0 root ffffffff S khelper root ffffffff S netns root ffffffff S modem_notifier root ffffffff S smd_channel_clo root ffffffff S smsm_cb_wq root ffffffff S kworker/u:1 root ffffffff S rpm-smd root ffffffff S kworker/u:1h root ffffffff S mpm root ffffffff S irq/47-cpr root ffffffff S sync_supers root ffffffff S bdi-default root ffffffff S kblockd root ffffffff S system root ffffffff S irq/282-msm_iom root ffffffff S irq/282-msm_iom

31 Quick guide to adb -mobile-12456

32 Native SW libraries (C/C++) Surface Manager: Rendering of Views 2D graphics Media Framework: Manage different codec, e.g. mp3,h.264,mpeg4,etc. Rendering of Font types In process DB Open GL ES 2D and 3D graphics For Embedded systems Web engine (Bionic)C standard library Wrapped as Java libraries

33 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

34 JNI

35 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) Act 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) See:

36 Core libraries Core Java classes android.* java.*, javax.* junit.* org.apache.*, org.json.*, org.xml.* Doesn t include all standard Java SDK classes developer.android.com/reference/packages.html

37 Core libraries (some) android.app Provides access to the application model used by of all Android applications. android.content Contains classes for accessing and publishing data on the device (content sharing, Intent) Access to the package manager and resource manager. android.database Used to access data published by content providers and includes SQLite database management classes. android.graphics A low-level 2D graphics drawing API including colors, points, filters, rectangles and canvases. android.hardware Presents an API providing access to hardware such as the accelerometer and light sensor. android.opengl A Java interface to the OpenGL ES 3D graphics rendering API. android.os Provides basic operating system services, message passing, and inter-process communication on the device. android.media Provides classes to enable playback of audio and video. android.net A set of APIs providing access to the network stack. Includes android.net.wifi, which provides access to the device s wireless stack. android.provider A set of convenience classes that provide access to standard Android content provider databases such as those maintained by the calendar and contact applications. android.text Used to render and manipulate text on a device display. android.util A set of utility classes for performing tasks such as string and number conversion, XML handling and date and time manipulation. android.view The fundamental building blocks of application user interfaces. android.widget - A rich collection of pre-built user interface components such as buttons, labels, list views, layout managers, radio buttons etc. android.webkit A set of classes intended to allow web-browsing capabilities to be built into applications. See:

38 Android architecture: application framework Application framework: Set of services in the form of managers.

39 Android frameworks (not complete list) Activity Manager Controls all aspects of the application lifecycle and activity stack. 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. View System An extensible set of views used to create application user interfaces. 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.

40 Android architecture: app layer Application layer

41 Google play services

42 Layers.

43 Processes All of the default system functions of Android are provided as the server process type

44 Binder

45 System Services The System Services is a set of about services that provide the user applications with the information and capabilities necessary to work. All these services relay on the Binder framework to communicate and collaborate with each other. Also, applications can instantiate these services through Binder. Most are written in Java except for a couple of them, which are written in C/C++.

46 Booting sequence see:

47 How to program a mobile device Android applications are typically written in Java, using Eclipse or Android Studio (official IDE) Native Language in C/C++ Libraries for critical hw components Functions can be called from java Native application in C# Xamarin (commercial platform) Portability among OS JavaScript (running inside webkit engine) JS functions can call Android methods PhoneGap, Apache Cordova Set of js libraries, improves portability among OS Web applications jquery mobile

48 Interaction with cloud Mobile apps can interact with cloud to store data (photo, contacts, etc), and synchronize different devices Can call web-api to enrich the functionality of the application For example exploit open data

49 Security Security goals Protect sensible data of users, like contact and Protect system resources Protect an application from other applications Security mechanisms 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

50 Sandbox and permission Sandbox: Linux UID=1234 Application: UID 1234 DVM <uses-permission>. Resources android.permission.camera camera

51 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 Sandboxing prevents one app from being able to read data or modify the code of other apps installed on the system. This feature helps to contain malware and other security threats, so that even if a vulnerable app is cracked via an exploit (or a malicious app manages to get itself installed on a device), it can't be used to gain further access to other software or data stored on the device.

52 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.

53 Sandobox and permission Sandbox: Linux UID=1234 Application: UID 1234 Application: UID 1234 DVM DVM Resource camera

54 Defining a permission

55 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, )

56 Bird s eye view to application architecture User Interface Activity Fragment UI runs in a thread Main thread it should respond fast responsiveness Computation Service Broadcast receiver Separate thread Need mechanism to interact with UI Implements the business logic Data Preference File SQLite Network Content provider Many ways to store data

57 What an application is composed of?

58 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.

59 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

60 Questions?