Introduction to izOS Programming using a Hello World Example

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Software Development Community
Mobile Device Programming Subgroup
Hello World Series – Part I - IOS
Paul Hancock - 29 April 2012

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Agenda
 What do you need to get started?
 Objective C explained in 30 seconds
 Target Considerations: iPad vs. iPhone vs. Universal
 Hello World! … take I
 Adding graphical elements to the main window programmatically
 Hello World! … take II
 Building graphical elements to the main window using WYSIWYG “Interface Builder”
 Hello World! … take III
 Adding graphical elements onto subviews
 Not covered in this presentation:
 Design patterns and concepts required to create non-trivial applications (Delegation, Notifications, Core
Data, Storyboards, etc.)
 Getting your app on the AppStore and becoming rich

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What you’ll need to get started
 Intel-based Mac running OSX
 Development Environment
 Basic knowledge of object oriented programming
concepts
 Familiarity with event-driven programming models
 Can spell MVC (Model-View-Controller)
 15 minutes of spare time

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Development Environment
 IOS SDK / Xcode running on Mac OSX
 Available from the AppStore for Free
 Everything you need, including iPhone/iPad simulators
 Optional:
 IOS Devices
 Developer’s License ($99/year)
 Developer certificate allows signing applications
 Allows developer to download/test/debug apps on actual IOS
devices
 Provides access to developer resources (help, etc.)
 Allows developer to put app on appstore and get rich

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Model-View-Controller
 Every IOS application object should be one of these
 Model Object
 Contains data without any knowledge of the application logic or GUI
 View Object
 Interfaces to the user (buttons, scroll bars, etc.) without any knowledge of how
the data is organized
 Controller Object
 Manages the application logic. Has knowledge of the Model objects and the
View objects. Acts as the glue to keeps Model objects and View objects in
sync.
 Least reusable classes

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MVC Design Pattern
Sends Message Update Data
View Controller Model
Update the View Fetch Data needed by View
Controllers don’t tell Views what to display. Views ask Controllers for what they need

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Objective C in 30 seconds
 A very simple language, like C
 Superset of C
 Entry point is main();
 originally implemented as C preprocessor (as was C++)
 Objective C keywords begin with “@”, for example @synthesize
 Adds object-oriented paradigms
 Classes / Objects / Encapsulation / Inheritance / Polymorphism / etc.
 Allows only single inheritance (subclasses have exactly one superclass)
 All objects ultimately derived from NSObject (“NS” stands for Next Step)
 Cocoa Touch Framework (not part of Objective C)
 Rich set of frameworks/libraries to enable rapid and consistent development of IOS applications
 Further Reading:
 Programming in Objective-C (4th Edition) - Stephen G. Kochan
 Objective-C Programming: The Big Nerd Ranch Guide – Aaron Hillegass

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Objective C - Object/Method Notation
Object Method Definition within a Class Implementation
-(float)calculateAreaOfRectangleWithWidth:(float)x
andHeight:(float)y
{
return x*y;
}
Method Invocation by an object
…you might be expecting something like….
float area;
area = myObject->calculateAreaOfRectangle(23.7,12.0);

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Objective C - Object/Method Notation
Object Method Definition within a Class Implementation
-(float)calculateAreaOfRectangleWithWidth:(float)x
andHeight:(float)y
{
return x*y;
}
But no, you do it by sending a message to the object …I mean the receiver….
float area;
area = [myObject calculateAreaOfRectangleWithWidth:23.7
andHeight:12.0];
Arguments
Receiver Selector “calculateAreaOfRectangleWithWidth:andHeight:”

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Application Target Considerations
iPhone? iPhone Retna? iPad? The New iPad?
Device Screen Graphics
Resolution Resolution
iPhone 3Gs and earlier 320x480 pixels
320 x 480 points
iPhone 4 and 4s (Retna) 640x960 pixels
iPad and iPad 2 768x1024 pixels
768 x 1024 points
The New iPad (Retna) 1536x2048 pixels
 iPhone applications will run unmodified on iPads, but potentially with
degraded (pixelated) appearance (not recommended)
 CoreGraphics based on points, not pixels – vector graphics not impacted
 Xcode allows multiple images to be bundled as resources so that they appear
sharp on all displays

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Real Estate Considerations
 iPhone vs iPad
 Vastly different screen real estate calls for different approach
 iPhones use UINavigationController as the primary drill-down mechanism
 iPads can leverage greater real estate and use UISplitViewController
vs.
UINavigationController
UISplitViewController

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Additional Resources
 iOS Programming: The Big Nerd Ranch Guide (3rd Edition)
 Aaron Hillegass & Joe Conway
 Very structured and well written explanation of Cocoa architecture and
approach
 iPad iOS 5 Development Essentials or iPhone iOS 5 Development
Essentials
 Neil Smyth
 Best how-to guides from soup to nuts for getting an application onto the
AppStore
 iOS 5 Programming Pushing the Limits: Developing Extraordinary
Mobile Apps for Apple iPhone, iPad, and iPod Touch
 Rob Napier
 Not a beginner book

13. And Now….
Let’s fire up Xcode and write some apps!

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Hello World 1
Implementation Summary
 Programmatic approach (no WYSIWYG)
 Created “Empty” project
 AppDelegate Class
 Instantiates the window
 Added Application icons
 Modified AppDelegate to
 Change window background color
 Created a UIButton (declared in .h and initialized in .m)
 Set the size and position of the button
 Set the title to “Press Me”
 Set the action for pressing the button to call sayHello:

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Hello World 2
Implementation Summary
 Implement the main window graphically with Interface Builder
 Created “Empty” project
 AppDelegate Class
 Instantiates the window
 Added application icons
 Modified AppDelegate to
 Comment out the programmatic instantiation of the window
 Declare helloButton (using keyword IBOutlet), declare/implement sayHello action (using keyword IBAction)
 Created a new project file (IOS Interface->Window)
 Created MainWindow.xib
 Added object (cube icon), set class to HelloWorld2AppDelegate (acts as a placeholder until runtime)
 Changed background color, added button, set the title to “Press Me” with 46pt font
 Graphically make connections
 Set File’s Owner Class to UIApplication, set File’s Owner Delegate to HelloWorld2AppDelegate
 Connect helloButton (in AppDelegate) to graphical button object, connect touch up inside action to sayHello (in AppDelegate)
 Set Application Main Interface to MainWindow

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Hello World 3
Implementation Summary
 Implement graphical objects in a view, with a dedicated ViewController rather than
directly on window
 Created “Single View Application” project
 AppDelegate Class
 ViewController Class
 XIB
 Basic connections made for you
 Added application icons
 Modified ViewController to
 Declare helloButton (using keyword IBOutlet), declare/implement sayHello action (using
keyword IBAction)
 Edit xib
 Set background color, added button, set the title to “Press Me” with 46pt font
 Connect helloButton (in File’s Owner) to graphical button object, connect touch up inside
action to sayHello (in File’s Owner)