MDAD 2 - Introduction to the Android Framework

1. Android System, platform and application types

2. Bibliography 1. Wallace Jackson, Android Apps for Absolute Beginners, Apress, 2017 2. Peter Späth, Learn Kotlin for Android Development, Apress 2019 3. Android Application Fundamentals, http://developer.android.com/guide/topics/f undamentals.html 2

3. Google Android Platform Developed by Google Based upon Linux Virtual Machine (Dalvik) & ART Open Source 3

4. Android Platform • Android – OS – Platform • Application types – Activities – Services – Content providers – Broadcast Revceivers 4

5. NOT only a OS • Radio Firmware – Phone system • GSM/CDMA / UMTS • Linux – Kernel 4.x and 5.x • Android 11 and newer – Optimised forARM • User Space Libraries – Bionic – SQLite – WebKit • Application platform 5

6. Android Schematics 6

7. Kernel • OS • Not visible • Extended Machine – Hardware abstraction • Contains drivers • Manages – Processor – Peripherals • Audio • Video • GPS • WiFi – Input/Output – Network stack 7

8. Kernel - Optimizations • Memory Management – No swap – On demand application closing system • Power management – WAIT_LOCK • Specific IPC – Binder • AIDL • Synchronous call between processes 8

9. User Space Libraries • Programming libraries – Link between the kernel and programs – Screen display • printf (…) • scanf (…) – Network access • socket (…) • Bionic – Libc for Android 9

10. User Space Libraries • SQlite • WebKit • Surfaces • FreeType • Media Framework • OpenGL|ES • SSL • … 10

11. Hardware Abstraction Layer • Drivers – hardware dependent – vendor dependent – have to be licensed as GPL • Drivers are abstracted by a service – the service is changed when hardware is changed 11

12. Dalvik - Android Runtime • Virtual Machine(Java) – Java 1.5 SE • Most of it • Missing – AWT / Swing – Imprimare – Alte componente speciale – Optimised for mobile • Small memory • Fast garbage collection – Different file format • .class -> .dex • JIT Compiler 12

13. Dalvik JIT 13

14. ART - Android Runtime • Environment for compiler and executer – Dalvik – Different file format • .dex -> .elf and odex • AOT • Includes a memory allocator 14 https://source.android.com/devices/tech/dalvik

15. Android ART 15

16. Android ART 16

17. Android ART 17 https://source.android.com/devices/tech/dalvik

18. ART Performance 18

19. Android Libraries • For Dalvik/ART – Not user space libraries! • Written in Java/Kotlin • Access to the device’s functions – Phone – Messages – Sensors • Services – Window Manager – Audio Manager 19

20. Android Schematics 20

21. Programming • Dalvik/ART (Application) – in Java/Kotlin – High speed – Access to many libraries • AJAX – In the browser (WebKit) – Slow – JavaScript • Native Development Kit (NDK) – C/C++ – Limited number of libraries – High speed – JNI Support – Not recommended for standard applications • C/C++ (services, used by vendors) 21

22. Application Security • Implemented in the kernel – Linux policy • Ext3 file system • SELinux • Users can write only in their folder – Every application runs with its own user • Determined by the digital signature! • Group permissions – May write in • /data/name.package.application / • /SDCard/ – Works for any application type • Dalvik / AJAX / NDK / C/C++ 22

23. Application Security • Implemented in the Android Libraries and Services – Permissions • Declared in the Manifest • Access device’s functions – Network – Phone / messages – Photo – GPS • Access to another application’s components – Permissions imposed by that application – User will be asked – at install (Android < 6) – at usage (Android >= 6) – Works only for Dalvik / ART applications – Native services have to check permissions themselves 23

24. Application & Services (Dalvik/ART) • There is no main() • Formed of components – Activities – Services – Content Providers – Broadcast Receivers • Components can run separately 24

25. Application Bundle (Dalvik/ART) • APK File – JAR uncompressed • Components – .dex File • Resources – Images – XML Files • Manifest – File with information – Digital signature • For development • For production – Authentic – Self signed 25

26. Task (UI Application) • Runs in one process – usually! – There are exceptions • Stack of activities • Root activity – Add • Display • push – Remove • Hide • pop – Activities from other applications 26

27. Task (UI Application) • Runs in one process – usually! – There are exceptions • Stack of activities • Root activity – Add • Display • push – Remove • Hide • pop – Activities from other applications 27

28. Activity 28

29. Important Functions • Class Activity – void onCreate (…); – void onStart (…); – void onRestart (…); – void onResume (…); – void onPause (…); – void onStop (…); – void onDestroy (…); • Must call parent functions – super.onCreate (…); – … 29

30. Activity • Window • Longer than the process – Serializing – Partially controlled by the programmer • Not for a lot of processing 30

31. Storing and loading of the status • Store – void onSaveInstanceState (Bundle state) • Load – void onLoadInstanceState (Bundle state) – void onCreate (Bundle savedInstance) 31

32. Services • Android Component • Specially for processing • Runs in background • process – Low priority – More stable (in time) 32

33. Service implementation • Extends class Service – Simple Service • void onCreate (); • void onStart (Intent intent, int startID); • void onDestroy (); – Using AIDL • void onBind (Intent intent); • void onUnbind(); 33

34. Content Providers / Broadcast Receivers • Content providers – Offer information – Link with SQLite – Based on URLs • Broadcast receivers – Observers – Public events • SCREEN_ON • SCREEN_OFF • BATTER_STATUS_CHANGED 34

35. Context • Context – any application component • Activities • Services • Content Providers – Generated by Dalvik/ART • at startup • provided as a parameter – Broadcast Receivers 35

36. Simulator vs. Real Phone • Simulator – Real • Boots Linux – Several versions – Runs separately • Real Phone – USB Debugging • Applications/Development • If you have an extra phone, use that one 36

37. Application template • AndroidManifest.xml • build.gradle • build (compiled files) • libs (libraries) • src (source files) • res – drawable – layout – values • assets (resources) • gen (Resources IDs (automatically generated)) • java • jni 37

38. Conclusions • Android Platform – Linux OS – Set of libraries for Android • Programming ways – Dalvik/ART – Java/Kotlin – AJAX – Web – NDK – C/C++ • Android Applications are a set of components – Activities – Services – Content Providers – Broadcast Receivers – There is no main() • Real emulator • Task – UI Applications – Set of Activities • Survive the process 38

39. Keywords • Operating System – Kernel – User Space Library • Linux – Process • Dalvik – Activity – Service – Content Provider – Broadcast Receiver • ART • Emulator • Security • Kernel (file system) • User Mode (Dalvik/ART) • Task – Activities Stack • Application State – Running – Paused – Stopped – Destroyed – Event • method call 39

40. Questions 40

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