Android 101 - Getting to know the basics of Android for developers.

1. Climbing Mount Android
Dr. Rajesh Vasa, 2011
Twitter: @rvasa
http://www.rvasa.com
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2. Mobile Eco-System
Content Providers
(Music/Video/Books)
Ad Networks App.
Distribution
Platform
Billing
Telephone Handset Cloud
Networks OEMs Infrastructure
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3. Android Eco-System
Content Providers
(Music/Video/Books) Google, Amazon
App.
Ad Networks ** Distribution
Google, Double Click
Platform Google Checkout
Android Billing
Google, Amazon
Telephone Handset Cloud
Networks (OEMs) Infrastructure
Samsung, HTC, Motorola, Sony ...
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4. Focus of this talk...
Content Providers
(Music/Video/Books) Google, Amazon
App.
Ad Networks ** Distribution
Google, Double Click Android Google Checkout
Platform Billing
Google, Amazon
Telephone Handset Cloud
ThisNetworks
talk will present a(OEMs)
development perspective
Infrastructure
Samsung, HTC, Motorola, Sony ...
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5. Talk Overview
• Devices
• What is Android?
• Development Tools
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Activities
• Activity Life Cycle (the odd thing)
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6. Roadmap - Where are we?
• Devices
• What is Android?
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Activities
• Activity Life Cycle (the odd thing)
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7. Android Device User Interaction
Android devices have
three key buttons
Menu
Back Home
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8. Vendors can add additional buttons
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9. There are variations in physical form
But all phones have Home, Menu, & Back Buttons
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10. Home Button...
• Typically, this will take you back to the Home
Screen of the phone
• Default behaviour ~ iPhone / iPad button
Home
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11. Back Button
• This will take you back to the previous screen
• If app. has only one screen, this will exit app.
Personal Opinion:
Back iPhone / iPad should
borrow this button
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12. Menu Button
• Shows a contextual menu (if one is available)
• Developers can write their own menus
• to low discoverability)
Quite handy (but, causes Usability issues due
Menu (as open)
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13. Android for tablets is slightly different...
Action Bar
Where is the menu button?
Back, Home
(Buttons need not be physical in Android)
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14. Tablet Menu Icon Visibility is contextual
Menu
Sadly, menu position is not mandated (yuk?)
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15. Roadmap - Where are we?
• Devices
• What is Android?
• Development Tools
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Activities
• Activity Life Cycle (the odd thing)
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16. What is Android?
• Android is a platform
• Operating System (with primitive API)
• Frameworks (incl. components and libraries)
Applications
Frameworks
Android
API
Operating System
(Customised Linux Kernel)
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17. Android
Programming languages: Java, C/C++
Image Source: http://developer.android.com
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18. Android is a bi-lingual platform
C/C++ Java
Image Source: http://www.tbray.org
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19. Most Android Code is in Java (but...)
≠
Android Java is not 100% Sun Java
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20. Android Java is different
No RMI
No Bytecode
No AWT / Swing UI
Different 2D/3D libs
Different Class Load Mechanism
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21. Roadmap - Where are we?
• Devices
• What is Android?
• Development Tools
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Activities
• Activity Life Cycle (the odd thing)
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22. Development Tools
• Android SDK (Compiler and Emulator)
• Eclipse IDE + Android Plug-in
• Powerful debugger
• Visual UI Builder
• Ant (Build System)
Download from http://developer.android.com
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23. Eclipse IDE
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24. Eclipse IDE - Graphical UI Editor
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25. Android Emulator
Permits checking Portrait
and Landscape views
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26. Emulator is nice .. but phone is better
• The emulator runs the Android O/S (you can
run any version: 1.6 upwards -- incl. tablet)
• Emulates the phone hardware (like VM Ware)
• Emulator does not have sensors (e.g. GPS,
Gyro, Accelerometer, Cell phone etc.)
• It offersevents methods to simulate some
sensor
primitive
• Interesting factoid: Youphonesend an it to
the emulator or make a
can
call to
SMS
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27. Emulators Vs Simulator
• iOS offers a simulator
• Android has gone down the emulator path
• Trade-offs (pros and cons),
• Simulators start-up faster, good enough
• Emulators allow closer to phone hardwareof
the O/S easily +
checking against rel. 2.1
• Emulators and Simulators cannot mimic real
CPU speed, disk speed, network speed etc.
(yet?)
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28. If your Java is rusty
Free e-Book: http://www.mindview.net/Books/TIJ/
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29. Roadmap - Where are we?
• Devices
• What is Android?
• Development Tools
•The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Activities
• Activity Life Cycle (the odd thing)
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30. The Android Way
Convention
Configuration
Development is organised around a few conventions
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31. Android Project Structure (convention)
•Source code (src)
•Generated code (gen)
•Resources (res)
•Images (drawable)
•Layout of app (layout)
•Constants/Strings (values)
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32. Needs Resources @Multiple Resolutions
Convention
High
Low
Medium
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33. Roadmap - Where are we?
• Devices
• What is Android?
• Development Tools
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Screens (Activities)
• Activity Life Cycle (interesting design choice)
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34. A Simple Android App.
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35. What is involved?
• Place UI controls (Text and Image)
• Layout the controls
• Centre text
• Make text large font
• Display Image to take up all space
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36. Each Screen is an Activity
• Android app. is made up of Activities
Activity
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37. Views are Android’s Key UI Building Block
• We need two views on the Activity
TextView
ImageView
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38. Views are Placed inside a View Group
• Different types of pre-defined layouts
• Linear, Relative, Table, Frame etc..
View Group
a.k.a Layout
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39. Android App. - Building Blocks
Activity Layout Views
(View Group)
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40. Separation of Concerns in Android
Presentation Functionality
Layout Definition Activity Class
(main.xml)
Event Handling, I/O ...
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41. UI (Layout) Definition
• Layout definition is generally in an XML file
• Hand coded or Visual Editor
• Can be also be done in Java Code (yuk!)
Layout Definition XML File
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42. Android Offers a number of UI Controls
• Offers all standard controls and lot more...
Progress
These are
a small
subset of
available
controls
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43. View Groups (Layouts for us mortals)
• Android offers the following View Groups,
• Linear Layout (Horizontal or Vertical)
• Absolute Layout (You set X, Y for each View)
• Table Layout (Rows and Columns)
• Relative Layout ( )
Position relative to other Views
• Frame Layout (Show only one view at a time)
• Scroll View (Permits scrolling of the screen)
•View Groups can be nested
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44. Generated Code, Layout & Resources
• How did Australia image get into the App.?
• How did we set the text to “Australia”?
• Conventions
• Layout Defined in /layout/main.xml
• Resources Placed in /res/drawable-*
• String values defined in/values/strings.xml
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45. Resources
Resources in “res”
Convention
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46. Resources are given a unique ID
A unique reference id
to resources is
generated by the
Android SDK tools
Convention
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47. Resources and Generated IDs
Generated Code
static final int australia=0x7f020000;
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48. A Reference to Layout also Generated
All References are Integers
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49. Identifiers are used to access resources
This is the Activity Class
Reference to the layout
(Android Runtime will Render this Layout)
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50. Layout is Referred to from Java Code
Activity Activity Class (Java)
View Group
(Layout)
Layout Definition
(main.xml)
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51. Who writes the Activity code?
This block of code is created by IDE/SDK
when we create new Android project
You can also write you own
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52. Activity Creation
Method called (by Application Launcher)
when App is first launched
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53. Activity Creation - Layout Rendering
Method call will pass the reference to the layout
that needs to be rendered on the screen
(“Rendering” is a two-pass process: measure and draw)
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54. What is the “root” Activity?
• How does Android know which Activity to
create first?
Answer: Application Manifest File
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55. Application Manifest File
Application Icon Reference
Activity Name Category
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56. Application Manifest File
Category indicates that it can be launched
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57. Application Manifest File
Main action indicates that it is the starting point
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58. Layouts and String Information
• How did we set the text to “Australia”
String constant
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59. Using Graphical Resources
• How did the Australia image get into layout?
Layout can refer to resources
@drawable is a special tag
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60. What is it with the @ tag?
• Constant Resources in Android can be
referred using the “@” tag in XML layout
• Example: @drawable, @string ...
@drawable/australia
@drawable/bots
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61. @ Tag and Multiple Screen Resolutions
• Dealing with multiple screen resolutions
@drawable/icon
Android Runtime decides best resource to use based on
hardware capabilities
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62. Significance of hdpi/ldpi/mdpi
Different resolution images
High-Res, 240 dpi screen
Low-Res, 120 dpi screen
Med-Res, 160 dpi screen
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63. Roadmap - Where are we?
• Devices
• What is Android?
• Development Tools
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Screens (Activities)
• Life Cycle & interesting design choices
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64. Building an App with Simple Interaction
• Temperature Conversion (C -> F)
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65. Views
TextView
EditText
Button
TextView
4 Views (UI components) using a Linear Layout
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66. Linear Layout (View Group)
main.xml
(Layout)
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67. View Identifiers
• We need a way to identify components that
we created in the layout
• E.g. To read input data from the field
@+id TAG creates new identifiers
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68. UI Interaction Handling Pattern
• Component.setOn......Listener ( handler )
• E.g. button.setOnClickListener
• Handler is an anonymous inner class
• On...Listener handler = new On....Listener() {}
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69. UI Interaction Handling Pattern
The View identifiers
are defined in XML
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70. Roadmap - Where are we?
• Devices
• What is Android?
• Development Tools
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Screens (Activities)
• Life Cycle & interesting design choices
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71. Wiring up Multiple Activities
Contact List Activity Contact Details
Select
Back
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72. Activities are Stacked in Android
• All current activities are placed on a Stack
• Newly started activities come into foreground
Foreground/Active
Contact Details
Back button will
Background/
pop top most starts
Paused
activity from stack Contact List
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73. Activities are like mini-processes
• Android activities have their own life cycle
• Asynchronous Messaging -- called “Intents”
Communication between Activities is done by
message
Contact List Contact Details
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74. Async. messaging called “Intents”
intent
Contact List Contact Details
Activities communicate with each other via Intents
Think of an Intent as a message -- like email!
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75. Async. messaging called “Intents”
Activity-X Photo Viewer
view photo
intent
You can send a general purpose message (intent), all
applications capable of handling that Intent will respond
Framework prescribes conventions for common intents
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76. Roadmap - Where are we?
• Devices
• What is Android?
• Development Tools
• The Android Way
• Anatomy of a Simple Android Application
• An Interactive Android Application
• Dealing with Multiple Screens (Activities)
•Life Cycle (& interesting design choices)
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77. Android Activities are Managed by O/S
Application
Activities have a
parent application
Activity-A
Activity-B
Activity-C
Activity has Life Cycle
Application is NOT managed
directly by the O/S
Life Cycle is Managed by Android Framework
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78. Android Activity Life Cycle
Activity is re-started when
orientation changes
Developers have to save
and retrieve state if
orientation changes
No, I am not kidding
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79. Security -- Android Devices
has
User UID (User ID)
also has determines
Android File System Access
Application Permissions
The UID is generated at install time based on
the signature and package name
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80. A Short Plug!!!
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81. Mobile Development @ Swinburne
• HIT8328(Lab work inDevelopment for Mobile
Devices
- Software
Android platform)
• HIT8329 - Creating Data Driven Mobile
Applications (iOS focused)
• Portfolio Based Assessment (no EXAM!)
• We do not focus only on API -- there is tostrong
conceptual foundation (preparing you
a
learn)
• Can study both subjects as single units
Follow @rvasa for updates
Swinburne University of Technology is in Melbourne, Australia
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