1. EEC-492/693/793 iPhone Application Development
Lecture 3
Wenbing Zhao & Nigamanth Sridhar
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EEC492/693/793 - iPhone Application Development

2. EEC492/693/793 - iPhone Application Development
Outline
Objective-C Property
Model-View-Controller
A primer on Objective-Oriented Design
Building the Button_Fun app
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EEC492/693/793 - iPhone Application Development

3. EEC492/693/793 - iPhone Application Development
Declared Properties
A convenience notation used to replace the declaration and implementation of accessor methods
In class interface, declare properties
@property BOOL flag
Each property specifies a method with the same name as the property
Each writable property specifies an additional method of the form setPropertyName
In the class implementation, compiler directive to ask the compiler to generate methods
@synthesize flag;
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EEC492/693/793 - iPhone Application Development

4. Objective-C Properties
declaration (in the .h file) is the Objective-C way of declaring the getters and setters
@property attributes
retain: tells the compiler to send a retain message to any object that we assign to this property => do not garbage collect it
Nonatomic: tells the compiler don’t bother adding thread-safety protections
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EEC492/693/793 - iPhone Application Development

5. Objective-C Properties
Dot notation: convenient way to accessing a property
myVar = someObject.foo;
Is equivalent to: myVar = [someObject foo];
someObject.foo = myVar;
Is equivalent to: [someObject setFoo: myVar];
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EEC492/693/793 - iPhone Application Development

6. Model-View-Controller
Model-View-Controller (MVC) is a design pattern commonly used for GUI-based apps
Model: the classes that hold your app’s data
View: made up of the windows, controls, and other elements that the user can see and interact with
Controller: binds the model and view together and is the application logic that decides how to handle the user’s inputs
Goal in MVC: make the objects that implement these three types of code as distinct from one another as possible
MVC helps ensure maximum reusability
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7. EEC492/693/793 - iPhone Application Development
Model
Manages the app data and state
Not concerned with UI or presentation
Often persists somewhere
Same model should be reusable, unchanged in different interfaces
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8. EEC492/693/793 - iPhone Application Development
View
Present the Model to the user in an appropriate interface
Allows user to manipulate data
Does not store any data
Except to cache state
Easily reusable & configurable to display different data
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Controller
Intermediary between Model & View
Updates the view when the model changes
Updates the model when the user manipulates the view
Typically where the app logic lives
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EEC492/693/793 - iPhone Application Development

10. Model-View-Controller
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11. Model-View-Controller
outlets
actions
Model Object
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12. Object Oriented Programming
Objects
Classes
Inheritance
Polymorphism
Taken from
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13. EEC492/693/793 - iPhone Application Development
Objects
Objects are the central idea behind OOP
An object is a bundle of (instance) variables and related methods
The concept of object makes it easier to capture and simulate the states and activities of real word objects programmatically
A method is an operation which can modify an object’s behavior (by changing its variables)
In general, variables in an object should be modified by one of the object’s methods
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14. EEC492/693/793 - iPhone Application Development
Classes
A class is a blueprint (i.e. specification) for an object
A class does not represent an object; it represents all the information a typically object should have as well as all the methods it should have
Instantiation: an object is created based on the class specification
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15. EEC492/693/793 - iPhone Application Development
Inheritance
A class C2 can be defined to be the subclass of another class C1
C2 inherits C1, i.e., C2 will have everything C1 has (both data and behavior)
C2 can use, augment, or replace C2’s methods
To do: what UIControl generic behavior is defined?
Memory
management
NSObject
C1 (superclass)
Generic
behaviors
UIControl
C2 (subclass)
Specific
behaviors
UIButton
UITextField
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16. EEC492/693/793 - iPhone Application Development
Polymorphism
Polymorphism refers to the ability of objects belonging to different classes to respond to the same message, each one according to an appropriate type-specific behavior
The programmer does not have to know the exact type of the object in advance => the exact behavior is determined at run-time
Different objects involved only need to present a compatible interface to clients
Usually, objects types are often implemented as subclasses of the same superclass
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17. Inheritance with Polymorphism
If a Dog is commanded to speak(), it may emit a bark
If a Pig is asked to speak(), it may respond with an oink
Both Dog and Pig inherit speak() from Animal, but their subclass methods override the methods of the superclass
Inheritance combined with polymorphism allows class B to inherit from class A without having to retain all features of class A; it can do some of the things that class A does differently
Calling code can issue the same command (sending the same message) to their superclass and get different results
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18. EEC492/693/793 - iPhone Application Development
Benefits of OOP
Encapsulation: states (variables) are changed via appropriate methods rather than changed directly by calling code
This drastically helps with understanding of the code and eliminating potential bugs
Modularity: different programmers or teams can work on different independent objects
Inheritance & polymorphism
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19. EEC492/693/793 - iPhone Application Development
The Button Fun App
Creating the project
Choose view-based application, name it “Button Fun”
Creating the view controller
Outlets and actions
Adding actions and outlets to the view controller
Chapter 3
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20. EEC492/693/793 - iPhone Application Development
Xcode Generated Code
Our view controller
Button_FunViewController.h
Button_FunViewController.m
Content of the header file
Our view controller is a subclass of UIViewController, which is part of the UIKit
#import <UIKit/UIKit.h>
@interface Button_FunViewController : UIViewController { }
@end
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Outlets and Actions
In the button fun app, we will have two buttons and one label, which we will create in the IB. The question is: how do we interact with them programmatically?
The answer is: through outlets and actions
Outlet: a special kind of instance variable by which our controller class can refer to objects in the nib file
E.g., controller can read the text of a label or modify it
Action: interface objects in our nib file can be set up to trigger special methods (i.e., actions) in our controller class
E.g., when a user touches up (i.e., pulls a finger off the screen) within a button, a specific action method should be called
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EEC492/693/793 - iPhone Application Development

22. EEC492/693/793 - iPhone Application Development
Outlets
Outlets are declared using the keyword IBOutlet, as in the example:
@property (nonatomic, retain) IBOutlet UIButton *myButton;
Actions are methods in the controller class
(IBAction)doSomething:(id)sender;
An action method has to return IBAction type (equivalent to “void”)
If you want to know the control that triggered the action, you should provide the (id)sender argument
In our app, we will use the sender arg. Because we want to know which button was tapped
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EEC492/693/793 - iPhone Application Development

23. Add Actions and Outlets to View Controller (part1)
Add declaration to the header file to:
#import <UIKit/UIKit.h>
@interface Button_FunViewController : UIViewController {
UILabel *statusText; }
@property (nonatomic, retain) IBOutlet UILabel *statusText;
- (IBAction)buttonPressed:(id)sender;
@end
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EEC492/693/793 - iPhone Application Development

24. Add Actions and Outlets to View Controller (part 2)
Add implementation to Button_FunViewController.m
@synthesize statusText;
// tell the compiler to automatically create the accessor and mutator methods
for us
- (IBAction)buttonPressed:(id)sender {
NSString *title = [sender titleForState:UIControlStateNormal];
NSString *newText = [[NSString alloc] initWithFormat:
button pressed.", title];
statusText.text = newText;
[newText release]; }
Sender will point to the button that was tapped
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EEC492/693/793 - iPhone Application Development

25. Add Actions and Outlets to View Controller
Add implementation to Button_FunViewController.m
(void)viewDidUnload {
self.statusText = nil;
//you need to set any outlets your class has to nil
// in viewDidUnload. }
- (void)dealloc {
[statusText release]; //release the outlet
[super dealloc];
@end
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Creating the View in IB
Double-click Button_FunViewController.xib
Add a label towards the bottom of the view, and two buttons side-by-side in the middle of the view
Pay attention to the guidelines while placing the controls
Change the text alignment to centered at the inspector
Double-click the label and remove existing text
Add text “Left” to the left button, “Right” to the right button
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EEC492/693/793 - iPhone Application Development

27. Connecting Everything
Connecting outlets: control drag from File’s Owner to the control
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Specifying Actions
Bring up connections inspector by pressing ⌘2 (or Tools -> Connection Inspector)
For left button, under the heading Events, select “Touch Up Inside”
This is an event when the user’s finger lifts up from the screen and the last place it touched before lifting was inside the button
Associate the event with the action
Click the circle right of “Touch Up Inside” and drag over to the “File’s Owner” icon
When the gray menu pops up, select “buttonPressed:”
Repeat for right button
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29. EEC492/693/793 - iPhone Application Development
Trying It Out
Save your project
Select “Build and Run”
Play with the app in the simulator
Test on your device
Rebuild the app for your device
ssh the app folder to your device
Respring on your device, you will see your app
Tap on your app to start it
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EEC492/693/793 - iPhone Application Development