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Your First iOS ApplicationGeneral

2011-03-08



Apple Inc.

© 2011 Apple Inc.

All rights reserved.

No partof this publication maybe reproduced,

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Apple Inc., with the following exceptions: Any

person is hereby authorized to store

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documentation for personal use provided that

the documentation contains Apple’scopyright

notice.

The Apple logo is a trademark of Apple Inc.

No licenses, express or implied, are grantedwith respectto anyof thetechnology described

in this document. Apple retains all intellectual

property rights associated withthe technology

described in this document. This document is

intended to assist application developers to

develop applications only for Apple-labeled

computers.

Apple Inc.

1 Infinite Loop

Cupertino, CA 95014

408-996-1010

App Store is a service mark of Apple Inc.

Apple, the Apple logo, Cocoa, Cocoa Touch,Instruments, iPhone, Mac, Objective-C, and

Xcode are trademarks of Apple Inc., registered

in the United States and other countries.

iPad is a trademark of Apple Inc.

IOS is a trademark or registered trademark of

Ciscoin theU.S.and othercountriesand isused

under license.

Even though Apple has reviewed this document,APPLEMAKESNO WARRANTYOR REPRESENTATION,EITHER EXPRESS OR IMPLIED, WITH RESPECT TOTHIS DOCUMENT, ITS QUALITY, ACCURACY,MERCHANTABILITY, OR FITNESSFOR A PARTICULARPURPOSE. AS A RESULT, THIS DOCUMENT ISPROVIDED “AS IS,” ANDYOU,THE READER, AREASSUMING THEENTIRE RISK AS TO ITSQUALITYAND ACCURACY.

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Contents

Introduction Introduction 7

Organization of This Document 8

Chapter 1 Creating Your Project 11

Xcode 11

Application Bootstrapping 14

Recap 16

Chapter 2 Understanding Fundamental Design Patterns 17

Delegation 17

Model-View-Controller 17

Target-Action 18

Other Design Patterns 18

Chapter 3 Adding a View Controller 19

Adding a View Controller Class 19

Adding a View Controller Property 22

Creating the View Controller Instance 23

Setting Up the View 24

Housekeeping 25

Implementation Source Listing 26

Test the Application 27

Recap 28

Chapter 4 Inspecting the Nib File 29

A View Controller’s View Often Comes from a Nib File 29

File’s Owner 30

The View Outlet 31


Recap 34

Chapter 5 Configuring the View 35

Adding the User Interface Elements 35

Make Connections 39

Make the Text Field’s Delegate Connection 43

Testing 44

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Recap 45

Chapter 6 Implementing the View Controller 47

The User’s Name Property 47

The changeGreeting: Method 48

Configure the View Controller as the Text Field’s Delegate 49


Recap 51

Chapter 7 Troubleshooting 53

Code and Compiler Warnings 53

Check the Nib Files 53

Delegate Method Names 53

Chapter 8 Next Steps 55

Improve the User Interface 55

Create User Interface Elements Programmatically 55

Install the Application on a Device 56

Add More Functionality 56

Add Unit Tests 57

Appendix A Code Listings 59

HelloWorldAppDelegate 59

The header file: HelloWorldAppDelegate.h 59

The implementation file: HelloWorldAppDelegate.m 59

MyViewController 60

The header file: MyViewController.h 60

The implementation file: MyViewController.m 60

Document Revision History 63


CONTENTS



Figures

Chapter 3 Adding a View Controller 19

Figure 3-1 MyViewController 20

Figure 3-2 MyViewController 21





FIGURES



This tutorial shows how to create a simple iOS application. It has a text field, a label, and a button. You can

type your name into the text field and tap the button to say hello. The application updates the label’s text

to say “Hello, <Name>!”:

The goal is not to create a finely polished application, or on the other hand to get an application on screen

as quickly as possible, but to illustrate the Three T’s:

● Tools: How you create and manage a project using Xcode

● Technologies: How to make your application respondto user input usingstandarduser interface controls

● Techniques: The fundamental design patterns and techniques that underlie all Mac OS X development


INTRODUCTION

Introduction



A secondary goal is to point out other documents that you must also read to fully understand the iOS

development tools and techniques.

You should read this document if you are just starting development for iOS. You should use this tutorial to

get started even if you intend to develop solely for the iPad. Although the tutorial shows the iPhone user

interface, thetools and techniques you useare exactly thesame as those you useto developiPadapplications.

You must, though, already have some familiarity with the basics of computer programming in general and

the Objective-C language in particular. If you haven’t used Objective-C before, read through at least Learning

Objective-C: A Primer .

Important: To follow this tutorial, you must have installed the iPhone SDK and developer tools available

from the iOS Dev Center.

This document describes the tools that are available for iPhone SDK v4.3 and later—check that your version

of Xcode is at least 4.0.

To learn more about the technologies in Cocoa Touch, read iOS Technology Overview .

In this tutorial, little regard is given to the user interface. Presentation is, however, a critical component of a

successful iOS application. You should read the iOS Human Interface Guidelines to understand how the user

interface might be improved for a full-fledged application.

This tutorial does notdiscuss issuesbeyondbasic application development; in particular, it does notdescribe

how to submit applications to the App Store.

Organization of This Document

The tool you use to create Mac OS X applications is Xcode—Apple’s IDE (integrated development environment).

“Creating Your Project” (page 11) shows you how to create a new project and describes how an application

launches.

Whereas Xcode is the application you use to create and manage the project, Cocoa is the name given to the

collection of APIs that you use to develop programs for Mac OS X. You should typically use the highest level

of abstraction available to accomplish whatever task you want to perform. To create a desktop application,

you should use the Objective-C-based frameworks that provide the infrastructure you need to implement

graphical, event-driven applications.

To use the Objective-C frameworks effectively, you need to follow a number of conventions and design

patterns. Following the Model-View-Controller (or “MVC”) design pattern, the application uses a controller

object to mediate between the user interface (view objects) and the underlying representation of a track (a

model object).

● “Understanding Fundamental Design Patterns” (page 17) provides an overview of the design patterns

you’ll use.

● “Adding a View Controller” (page 19) shows you how to customize a view controller class and create an

instance of it.

You design the user interface graphically, using Xcode, rather than by writing code. The interface objects are

stored in an archive called a nib file.

8 Organization of This Document2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

INTRODUCTION

Introduction

http://developer.apple.com/iphone/index.action

http://developer.apple.com/iphone/index.action



Terminology: Although an interface document may have a “.xib” extension, historically the extension was

“.nib” (an acronym for “NextStep Interface Builder”) so they are referred to colloquially as “Nib files.”

The nib file doesn’t just describe the layout of user interface elements, it also defines non-user interface

elements and connections between elements. The controller object is represented in the nib file. At runtime,when a nib file is loaded the objects are unarchived and restored to the state they were in when you saved

the file—including all the connections between them.

● “Inspecting the Nib File” (page 29) introduces you to two important concepts: outlets, and the File’s

Owner proxy object

● “Configuring the View” (page 35) shows you how to add and configure the button and text fields.

● “Implementing the View Controller” (page 47) walks you through implementing the view controller,

including memory management, the changeGreeting:method, and ensuring that the keyboard is

dismissed when the user taps Done

● “Troubleshooting” (page 53) describes some approaches to solving common problems that you may

encounter.

● “Next Steps” (page 55) offers suggestions as to what directions you should take next in learning about

iOS development.

Organization of This Document 92011-03-08 | © 2011 Apple Inc. All Rights Reserved.

INTRODUCTION

Introduction



10 Organization of This Document2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

INTRODUCTION

Introduction



In this chapter, you create the project using Xcode and find out how an application launches.

Xcode

The main tool you use to create applications for iOS is Xcode—Apple’s IDE (integrated development

environment). You canalso use it to create a variety of other projecttypes, including Cocoa and command-line

utilities.

To create a new project . . .

1. Launch Xcode.

By default it’s in /Developer/Applications.

2. Create a new project by choosing File > New Project.

You should see a new window similar to this:

Xcode 112011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 1

Creating Your Project



3. In the left pane, choose iOS application.

4. Select Window-based Application then click Next.

5. In the Device popup menu, make sure iPhone is selected.

Do not select the option to use Core Data. The tutorial does not use Core Data.

Do not select the option to use unit tests. The tutorial doesn’t discuss how to set up unit tests; however,

you should consider using unit tests a best practice for Cocoa development.

6. Enter HelloWorld as the product name, and a suitable company identifier (if you don’t have one, use

edu.self).

Note: Theremainder of thetutorialassumes that you namedtheprojectHelloWorld, so theapplication

delegate class is called HelloWorldAppDelegate. If you name your project something else, then the

application delegate class will be called YourProjectNameAppDelegate.

7. Click Next.

A sheet appears to allow you to select where your project will be saved.

8. Select a suitable location for your project (such as the Desktop or a custom Projects directory), then click

Save.

You do not need to create a version control repository for this project, although in general you are

encouraged to do so.

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CHAPTER 1




You should see a new project window like this:

If you haven’t used Xcodebefore, take a moment to explore the application. You should read Xcode WorkspaceGuide to understand the organization of the project window and how to perform basic tasks like editing and

saving files. You can now build and run the application to see what Simulator looks like.

To run your application in Simulator . . .

● Choose Product > Run (or click the Run button in the toolbar).

The iOS Simulator application should launch automatically, and when your application starts up you should

simply see a white screen:

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CHAPTER 1




To understand where the white screen came from, you need to understand how the application starts up.

For now, quit Simulator.

To quit Simulator . . .

● Choose Simulator > Quit.

Application Bootstrapping

Thetemplate project you created already sets up the basic application environment. It creates an application

object, connects to the window server, establishes the run loop, and so on. Most of the work is done by the

UIApplicationMain function.

The main function in main.m calls the UIApplicationMain function:

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CHAPTER 1




int retVal = UIApplicationMain(argc, argv, nil, nil);

This creates an instance of UIApplication. It also scans the application’s Info.plist property list file.

The Info.plist file is a dictionary that contains information about the application such as its name and

icon. It may contain the name of the nib file the application object should load, specified by the

NSMainNibFile key. Nib files contain an archive of user interface elements and other objects—you’ll learn

more about them later in the tutorial. In your project’s Info.plist file you should see:

ValueKey

MainWindowNSMainNibFile

This means that when the application launches, the MainWindow nib file is loaded.

To look at the main nib file . . .

● Click MainWindow.xib in the Resources group in the project window

The file has the extension “xib” but by convention it is referred to as a “nib file”. Xcode displays the file

in the editor area.

The nib file contains several items split into two groups by a dividing line. Above the line are placeholders:

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CHAPTER 1




● The File’s Owner proxy object (the pale yellow cube).

The File’s Owner object is actually the UIApplication instance—File’s Owner is discussed later, in

“File’s Owner” (page 30).

● A First Responder proxy object.

The First Responder is not used in this tutorial but you can learn more about it by reading “The

Event-Handling System” in iOS Application Programming Guide.

Below the line are actual objects:

● An instance of HelloWorldAppDelegate set to be the application’s delegate.

Delegation is explained in more detail in “Understanding Fundamental Design Patterns” (page 17).

● A window.

The window has its background set to white and is set to be visible at launch. It ’s this window that you

see when the application launches.

You use the application delegate to perform custom configuration for the application as a whole, including

displaying the window. It shouldn’t, though, manage any of the content on the screen beyond the window

itself—that’s the job of view controllers. A view controller is a special controller responsible for managing

a view—this adheresto themodel-view-controllerdesign pattern (explained in more detail in “Understanding

Fundamental Design Patterns” (page 17)).

When the application object has completed its setup, it sends its delegate an

application:didFinishLaunchingWithOptions:message. This gives the delegate an opportunity to

configure the user interface and perform other tasks before the application is displayed.

Recap

In this chapter you created a new project using Xcode and built and ran the default application. You also

looked at some of the basic pieces of a project and a nib file, and learned how the application starts up. In

the next chapter, you’ll learn about the design patterns you use when developing a Cocoa application.

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CHAPTER 1




In this chapter, you learn about the main design patterns you’ll use in Cocoa applications. There’s not much

practical to do in this chapter, but the concepts are fundamental, so allow some time to read and think about

it.

The main patterns you’re going to use in this tutorial are:

● Delegation

● Model-View-Controller

● Target-Action

Here’s a quick summary of these patterns and an indication of where they’ll be used in the application.

Delegation

Delegation is a pattern in which one object sends messages to another object specified as its delegate to

ask for input or to notify the delegate that an event is occurring. You typically use it as an alternative to class

inheritance for extending the functionality of reusable objects.

In this application, the application object tells its delegate that the main start-up routines have finished and

that the custom configuration can begin. For this application, you want the delegate to create an instance

of a controller to set up and manage the view. In addition, the text field will tell its delegate (which in this

case will be the same controller) when the user has tapped the Return key.

Delegate methods aretypically grouped together into a protocol.A protocol is basically just a list of methods.

If a class conforms to (or “adopts”) a protocol, it guarantees that it implements the required methods of a

protocol. (Protocols may also include optional methods.) The delegate protocol specifies all the messages

an object might send to its delegate. To learn more about protocols and the role they play in Objective-C,

see the “Protocols” chapter in The Objective-C Programming Language.

Model-View-Controller

The Model-View-Controller (or “MVC”) design pattern sets out three roles for objects in an application.

Model objects represent data such as SpaceShips and Weapons in a game, ToDo items and Contacts in a

productivity application, or Circles and Squares in a drawing application.

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CHAPTER 2

Understanding Fundamental Design Patterns



In this application, the model is very simple—just a string—and it’s not actually used outside of a single

method, so from a practical perspective in this application it’s not even necessary. It’s the principle that’s

important here, though. In other applications the model will be more complicated and accessed from a

variety of locations.

View objects know how to display data (model objects) and may allow the user to edit the data.

In this application, you need a main view to contain several other views—a text field to capture information

from the user, a second text field to display text based on the user’s input, and a button to let the user tell

us that the secondary text should be updated.

Controller objects mediate between models and views.

In this application, the controller object takes the data from the input text field, stores it in a string, and

updates a second text field appropriately. The update is initiated as a result of an action sent by the button.

Target-Action

The target-action mechanism enables a view object that presents a control—that is, an object such as a

button or slider—in response to a user event (such as a click or a tap) to send a message (the action) to

another object (the target) that caninterpret themessage andhandle it as an application-specific instruction.

In this application, when it’s tapped, the button tells the controller to update its model and view based on

the user’s input.

Other Design Patterns

Cocoa makes pervasive use of a number of design patterns beyond those described above. The design

patterns chapter in Cocoa Fundamentals Guide provides a comprehensive overview of all the design patterns

you use in Cocoa application development—you should consider it to be essential reading. Understanding,

andusing, the patterns will make it easier for you to usethe various technologies Cocoa provides, andtransfer

skills you’ve learned in one are to another. Following the patterns also means that your code will work better

with Cocoa.

18 Target-Action2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 2

Understanding Fundamental Design Patterns



In this application you’ll need two classes. Xcode’s application template provided an application delegate

class and an instance is created in the nib file. You need to implement a view controller class and create an

instance of it.

Adding a View Controller Class

View controller objects play a central role in most iOS applications. As the name implies, they’re responsible

for managing a view, but on iOS they also help with navigation and memory management. You’re not going

to use the latter features here, but it’s important to be aware of them for future development. UIKit providesa special class—UIViewController—that encapsulates most of the default behavior you want from a view

controller. You have to create a subclass to customize the behavior for your application.

To add a custom view controller class . . .

1. In Xcode, in the project organizer select either the project (HelloWorld at the top of the Groups and

Files list) or the HelloWorld group folder.

The new files will be added to the current selection.

2. Choose File > New File and in the New File window.

You should see a sheet like this:

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CHAPTER 3

Adding a View Controller



3. Select the Cocoa Touch Classes group, then select UIViewController subclass.

4. Click Next.


Figure 3-1 MyViewController

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CHAPTER 3




5. Using the combo box, choose to create a subclass of UIViewController.

6. Using thecheckboxes,make sure that Targeted for iPad is not selected,and that With XIB for user interface

is selected.

7. Click Next.


Figure 3-2 MyViewController

Make sure the Add to targets check box is selected.

8. Give the file a new name such as MyViewController.

By convention, class names begin with a capital letter.

9. Click Save.

Make sure that the files were added to your project.

If you look at the new source files, you’ll see that stub implementations of various methods are already givento you. These are all you need for the moment; the next task is to create an instance of the class.

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CHAPTER 3




Adding a View Controller Property

You want to make sure that the view controller lasts for the lifetime of the application, so it makes sense to

add it as a property of the application delegate (which will also last for the lifetime of the application). (To

understand why, consult Memory Management Programming Guide.)

Perform thefollowingtasks in theheader filefor theapplication delegate class (HelloWorldAppDelegate.h).

To add a view controller property . . .

1. Add a forward declaration for the MyViewController class.

Before the interface declaration for HelloWorldAppDelegate, add:

@class MyViewController;

The property will be an instance of the MyViewController class. The compiler will generate an error,

though, if you declare the variable but you don’t tell it about the MyViewController class. You could

import the header file, but typically in Cocoa you instead provide a forward declaration—a promise to

the compiler that MyViewControllerwill be defined somewhere else and that it needn’t waste time

checking for it now. (Doing this also avoids circularities if two classes need to refer to each other and

would otherwise include each other’s header files.) Later, you will import the header file itself in the

implementation file.

2. Add a declaration for the view controller property. After the closing brace but before @end, add:

@property (nonatomic, retain) MyViewController *myViewController;

Important: Like C, Objective-C is case-sensitive.MyViewController refers to a class; myViewController

is a variable that here contains an instance of MyViewController. A common programming error in Cocoa

is to misspell a symbol name, frequently by using a letter of an inappropriate case (for example, “tableview”

instead of “tableView”). This tutorial deliberately uses MyViewController and myViewController to

encourage you to look at the name carefully. When writing code, make sure you use the appropriate symbol.

Properties are described in the “Declared Properties” chapter in The Objective-C Programming Language.

Basically, though, this declaration specifies that an instance of HelloWorldAppDelegate has a property

that you canaccess using thegetter and setter methods myViewControllerandsetMyViewController:

respectively, and that the instance retains the property (retaining is discussed in more detail later).

To make sure you’re on track, confirm that your HelloWorldAppDelegate class interface file

(HelloWorldAppDelegate.h) looks like this (comments are not shown):

#import <UIKit/UIKit.h>


@interface HelloWorldAppDelegate : NSObject <UIApplicationDelegate> {

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CHAPTER 3




}

@property (nonatomic, retain) IBOutlet UIWindow *window;


@end

You can now create an instance of the view controller.

Creating the View Controller Instance

Now that you’ve added the view controller property to the application delegate, you need to actually create

an instance of the view controller and set it as the value for the property. To make code-completion work

for your new class in Xcode, you also need to import the relevant header file for the view controller.

Perform the following tasks in the implementation file for the application delegate class

(HelloWorldAppDelegate.m).

To import the view controller’s header file . . .

● At the top of file, add:

#import "MyViewController.h"

To add a view controller instance . . .

● Add the following code as the first statements in the implementation of the

application:didFinishLaunchingWithOptions:method:

MyViewController *aViewController = [[MyViewController alloc]

initWithNibName:@"MyViewController" bundle:[NSBundle mainBundle]];

[self setMyViewController:aViewController];

[aViewController release];

There’s quite a lot in just these three lines. What they do is:

● Create and initialize an instance of the view controller class.

● Set the new view controller to be the value of the myViewController property using an accessor

method.

Remember that you didn’t separately declare setMyViewController:, it was implied as part of the

property declaration—see “Adding a View Controller Property” (page 22).

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CHAPTER 3




● Adhere to memory management rules by releasing the view controller.

You create the view controller object using alloc, then initialize it using initWithNibName:bundle:. The

init method specifies first the name of the nib file the controller should load and second the bundle in

which it should find it. A bundle is an abstraction of a location in the file system that groups code and

resourcesthatcan be usedin an application. Theadvantages of using bundles over locatingresourcesyourself in the file-system are that: bundles provide a convenient and simple API—the bundle object can locate a

resource just by name; and they take account of localization for you. To learn more about bundles, seeResource Programming Guide.

By convention, you own any objects you create using an alloc method (amongst others, see “Memory

Management Rules”). You should also:

● Relinquish ownership of any objects you create.

● Typically use accessor methods to set property values anywhere other than in an initializer method.

Thesecond line in the implementation uses an accessor method to set the property value, andthen thethirdline uses release to relinquish ownership.

There are other ways to implement the above. You could, for example, replace the three lines with just two:

MyViewController *aViewController = [[[MyViewController alloc]

initWithNibName:@"MyViewController" bundle:[NSBundle mainBundle]]

autorelease];


In this version, you use autorelease as a way to relinquish ownership of the new view controller but at

some point in the future. To understand this, read “Autorelease Pools” in the Memory Management

Programming Guide. In general, however, you should try to avoid using autorelease wherever possible

since it means memory may be reclaimed later than it would be if you used release.

You could also replace [self setMyViewController:aViewController]; with:

self.myViewController = aViewController;

The dot notation invokes exactly the same accessor method (setMyViewController:) as in the original

implementation. The dot notation simply provides a more compact syntax for accessor methods—especially

when you use nested expressions. Which syntax you choose is largely personal preference, although using

thedotsyntaxdoes have some additional benefitswhen used in conjunctionwith properties—see“Declared

Properties” in The Objective-C Programming Language. For more about the dot syntax, see “Dot Syntax” in

The Objective-C Programming Language in “Objects, Classes, and Messaging” in The Objective-C Programming

Language.

Setting Up the View

View controllers are responsible for configuring and managing each “screenful” you see in an application.

Each screenful should be managed by a view controller. To codify this principle, a window has a root view

controller—the viewcontroller responsible for configuringthe viewfirstdisplayed when the window appears.

To get your view controller’s content into the window, you set your view controller to be the window’s root

view controller.

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CHAPTER 3




To set your view controller as the window’s root view controller . . .

● Add the following line of code just before the call to makeKeyAndVisible.

self.window.rootViewController = self.myViewController;

Instead of using the dot syntax, you could also use square brackets:

[[self window] setRootViewController:[self myViewController]];

Both lines of code would compile to the same thing; again you can choose which you feel is more readable.

A further important point about this line, though, is that it uses the accessor method to retrieve

myViewController.

Tip In addition to using accessor methods to set property values (except in the implementation of aninit method), you should use accessor methods to get property values, even those of self (except in

the implementation of a dealloc method). This helps to preserve encapsulation, and in some cases

ensures that a property value is properly initialized before you try to use it. This is discussed in more

detail in “Housekeeping” (page 25).

The final line in the implementation of the application:didFinishLaunchingWithOptions:method

from the template:

[window makeKeyAndVisible];

causes the window—now complete with your view—to be displayed on screen.

Housekeeping

There are a couple of unfinished tasks to complete: You need to synthesize the accessor methods, and—to

conform to the rules of memory management—make sure the view controller is released in the dealloc

method.

You perform the following tasks in the @implementation block of the class (HelloWorldAppDelegate).

To synthesize the view controller property . . .

● Tell the compiler to synthesize the accessor methods for the view controller, and to use a custom name

for the corresponding instance variable.

@synthesize myViewController=_myViewController;

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This line of code tells the compiler to do several things:

● Create accessor methods for the myViewController property.

Strictly speaking, it means “create accessor methods, according to the property declaration, for which

the developer hasn’t provided an implementation.” Since you haven’t created custom implementations,

the compiler will generate a get and set accessor. (If the property were declared as readonly, thecompiler would only generate a get accessor.)

● Use _myViewController as the name of the instance variable for the myViewController property.

● Because you didn’t declare a _myViewController instance variable, it also tells the compiler to add

that to the class as well.

You use the “_” prefix for the instance variable to serve as a reminder that you shouldn’t access an instance

variable directly. From an academic perspective, this helps to preserve encapsulation, but there are two

important practical benefits in Cocoa:

● Some Cocoa technologies (notably key-value coding) depend on use of accessor methods, and in theappropriate naming of the accessor methods. If you don’t use accessor methods, your application may

be less able to take advantage of standard Cocoa features.

● Some property values are created on-demand. If you try to use the instance variable directly, you may

get nil or an uninitialized value. (A view controller’s view is a good example.)

To complete the implementation of the dealloc method . . .

● In the dealloc method, release the view controller as the first statement.

[_myViewController release];

Implementation Source Listing

To make sure you’re still on track, confirm that your HelloWorldAppDelegate class implementation

(HelloWorldAppDelegate.m) looks like this (the methods you didn’t edit are omitted):

#import "HelloWorldAppDelegate.h"


@implementation HelloWorldAppDelegate

@synthesize window=_window;


- (BOOL)application:(UIApplication *)application

didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

26 Implementation Source Listing2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 3




{

MyViewController *aViewController = [[MyViewController alloc]

initWithNibName:@"MyViewController" bundle:nil];

self.myViewController = aViewController;



[self.window makeKeyAndVisible];

return YES;

}

/* Other methods omitted from the listing. */

- (void)dealloc {


[_window release];

[super dealloc];

}

@end

Test the Application

You can now test your application.

To test the application . . .

● Compile and run the project.

Choose Product > Run (or click the Run button in Xcode’s toolbar).

Your application should compile without errors and you should again see a white screen in Simulator.

Test the Application 272011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 3




Recap

In this section you addeda new view controller class and itsaccompanying nibfile. In the application delegate,

you declared an instance variable and accessor methods for a view controller instance. You also synthesized

theaccessor methods andperformeda fewother housekeeping tasks.Most importantly, though, youcreated

an instance of theview controller andpassed its to thewindow as theroot view controller. In thenext chapter

you’ll configure the nib file the controller uses to load its view.


CHAPTER 3




This chapter introduces two important concepts: outlets and the File’s Owner proxy object.

A View Controller’s View Often Comes from a Nib File

As you learned earlier, a view controller is responsible for configuring and managing each “screenful” you

see in an application. Each screenful is defined by the view controller’s view; often you configure that view

in a nib file (a common exception is a table view). Typically you specify the name of the nib file to load as

the first argument to initWithNibName:bundle: (see “Creating the View Controller Instance” (page 23)).

A view controller loads its nib file in its loadView method. (You can load nib files yourself using an instance

of NSBundle. You can learn more about loading nib files in Resource Programming Guide.) If you initialize a

view controller using initWithNibName:bundle: but you want to perform additional configuration after

the view is loaded, you override the controller’s viewDidLoad method.

The view controller’s nib file contains three objects, the File’s Owner proxy, the First Responder proxy, and

a view. You can see them by inspecting the nib file.

To inspect the nib file . . .

● In Xcode, click the view controller’s nib file (MyViewController.xib).

You should see the file displayed like this:

A View Controller’s View Often Comes from a Nib File 292011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 4

Inspecting the Nib File



The view is the main view for the view controller. The view controller is represented by the File’s Owner

proxy. It’s important to understand the role of File’s Owner, and how to create connections to and from both

File’s Owner and other objects.

File’s Owner

In a nib file, in contrast to the other objects you add to the interface, the File’s Owner object is not created

when the nib file is loaded. It represents the object set to be the owner in the method that loads the nib

file—inthiscase, loadNibNamed:owner:options: . This is discussed in more detail in Resource Programming

Guide. In your application, the File’s Owner will be the instance of MyViewController.

To allow you to make appropriate connections to and from the File’s Owner, Xcode has to know what sort

of object File’s Owner is. You tell Xcode the class of the object using the Identity Inspector. It was actually

set when you created the nib file together with the view controller classes, but it ’s useful to look at the

inspector now.

To show the inspector . . .

1. With the nib file selected, in Xcode display the Utilities view.

30 File’s Owner2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 4




2. In the Inspector pane, select the Identity inspector.

In the Classfield of the CustomClass section, you shouldsee MyViewController. It’s important to understand

that this is justa promise to InterfaceBuilder that the File’s Owner will bean instance of MyViewController.Setting the class doesn’t ensure that the File’s Owner will be an instance of that class. Remember, the File’s

Owner is simplywhatever object is passedas theowner argument to theloadNibNamed:owner:options:

method. If it’s an instance of a different class, the connections you make in the nib file will not be properly

established.

The View Outlet

You canlook at—andmake andbreak—anobject’s connections using theInspector pane,or in a connections

panel.

To look at the view controller’s connections . . .

1. In the Interface Builder editor window, click File’s Owner.

2. In the Inspector pane, select the Connections inspector.

This displays File’s Owner’s outlet connections in the utility area.

The View Outlet 312011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 4




3. In the Interface Builder editor window, Control-click File’s Owner.

This displays a translucent panel showing File’s Owner’s connections.

The utility area and the connections pane both show the same information. You can use whichever is more

convenient at any particular time.

The only connection at the moment is the view controller’s view outlet. An outlet is just a property that

happens to connect to an item in a nib file. The outlet connection means that when the nib file is loaded

and the UIView instance is unarchived, the view controller’s (strictly File’s Owner’s) view property is set to

that view.


To make sure your application’s workingcorrectly, youcould setthebackground color of theview to something

other than white and verify that the new color is displayed after the application launches.

To set the background color of the view controller’s view . . .

1. In Xcode, select the view controller’s nib file (MyViewController.xib).

32 Test the Application2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 4




2. In the utilities area, select the Attributes inspector.

3. In the editor area, select the view.

4. In theAttributes inspector for theview, click the frame of the Background color well to display theColors

panel.

5. In the Colors panel, select a different color.

6. Save the nib file.

7. Click the Run button in the toolbar to compile and run the project.

Your application should compile without errors and you should again see an appropriately-colored screen

in Simulator.

To restore the view’s background color . . .

1. In Xcode, using the attributes inspector, set the view’s background color to white.


Test the Application 332011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 4




Recap

In this section you inspected a nib file, learned about outlets, and set the background color of a view. You

also learned more about resource loading and how the view controller loads the nib file.

In the next chapter you will add controls to the view.


CHAPTER 4




Interface Builder provides a library of objects that you can add to a nib file. Some of these are user interface

elements such as buttons and text fields; others are controller objects such as view controllers. Your nib file

already contains a view—now you just need to add the button and text fields.

Adding the User Interface Elements

You add user interface elements by dragging them from the object library.

To add objects to the nib file and lay them out appropriately . . .

1. In Xcode, select the view controller’s nib file.

2. In the utilities area, display the object library.

3. Add a button (UIButton), a text field (UITextField), and a label (UILabel) to the view.

You can drag view items from the library and drop them onto the view just as you might in a drawing

application.

Adding the User Interface Elements 352011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5

Configuring the View



4. Lay out the elements appropriately.

You can then resize the items using resize handles where appropriate, and reposition them by dragging.

As you move items within the view, alignment guides are displayed as dashed blue lines.

36 Adding the User Interface Elements2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




5. Finalize the view.

● Add a placeholder string Your Name to the text field by entering it in the Text Field Attributes

inspector.

● Resize the label so that it extends for the width of the view.

● Delete the text (“Label”) from the label either using the Label Attributes inspector or by selecting

the text in the label itself (double-click to make a selection) and press Delete.

● Add a title to the button by double-clicking inside the button and typing Hello.

● Use the inspector to set the text alignment for the text field and label to centered.

Your view should look like this:

Adding the User Interface Elements 372011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




6. In the view section of the label’s Label Attributes inspector, select Clear Context Before Drawing.

This ensures that when you update the greeting the previous string is removed before the new one is

drawn. If you don’t do this, the strings are drawn on top of each other.

There are several other changes to make to the text field—it might be fairly obvious that the first change

applies to the text field, but the others are less obvious. First, you might want to ensure that names are

automatically capitalized. Second, you might want to make sure that the keyboard associated with the text

field is configured for entering names, and that the keyboard displays a Done button.

The guiding principle here is this: You know when you’re putting it on screen what a text field will contain.

You therefore design the text field to make sure that at runtime the keyboard can configure itself to best

suit the user’s task. You make all of these settings using text input traits.

To configure the text field . . .

1. Select the text field.

2. In the utilities area, display the attributes inspector.

3. Configure the text field using the Text Input Traits.

● In the Capitalize pop-up menu, select Words.

38 Adding the User Interface Elements2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




● In the Keyboard Type pop-up menu, select Default.

● In the Keyboard Return Key pop-up menu, select Done.


If you build and run your application in Xcode, when it launches you should see the user interface elements

as you positioned them. If you press the button, it should highlight, and if you tap inside the text field, the

keyboard should appear. At the moment, though, after the keyboard appears, there’s no way to dismiss it.

To remedy this, and add other functionality, you need to make appropriate connections to and from the

view controller. These are described in the next section.

Make Connections

You can create and connect outlets and actions in Xcode by dragging from a nib file to the appropriate

source file. Whereas this makes it easy to add code to support outlets and actions, it adds a conceptual level

of indirection. Although you’re dragging to the source file, the actual connections are made in the nib file

itself, to the object for which the header file is the declaration—in this case, the view controller represented

by File’s Owner.

You want to add an action method to the view controller; when the button is “activated” it should send a

changeGreeting: message to the view controller. For the button, you want to create an action called

changeGreeting::

To add an action for the button . . .


2. Display the Assistant editor.

3. Make sure Assistant displays the view controller’s header file (MyViewController.h).

4. Control drag from the button in the nib file to the method declaration area in the header file.

Make Connections 392011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




5. Configure the button’s connection as an action.

● Set the connection type to Action.

● Set the name to changeGreeting:.

● Set the type to id.

It doesn’t matter what sort of object sends the message.

● Set the event to touch up inside.

The message should be sent if the user lifts their finger inside the button—this corresponds to

UIControlEventTouchUpInside.

● Set the arguments to sender.

6. Click Connect.

You accomplished two things by adding an action for a button:

1. Added appropriate code to the view controller class.

You added the action method declaration to the header file:

- (IBAction)changeGreeting:(id)sender;

40 Make Connections2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




5. Configure the text field’s connection as an outlet.

Add an outlet from the view controller connected to the text field.

● Set the connection type to Outlet.

● Set the name to textField.

You can call the outlet whatever you want, but it makes your code more understandable if the name

bears some relationship with the thing it represents.

● Set the type to UITextField.

You want to make sure the outlet can only connect to a text field.

6. Click Connect.

You accomplished two things by adding an outlet for the text field:

1. You added appropriate code to the view controller class.

The property declaration to the header file:

@property (nonatomic, retain) IBOutlet UITextField *textField;

and other code the implementation file. It adds:

@synthesize textField;

to the top of the @implementation block;

[textField release];

to the dealloc method, and

[self setTextField:nil];

to the viewDidUnload method.

Property declarations and the synthesize keyword are explained in more detail in “The User’s Name

Property” (page 47).

IBOutlet is a special keyword that is used only to tell Interface Builder to treat a property as an outlet.

It’s actually defined as nothing so it has no effect at compile time.

2. You established a connection from the the view controller (as represented by the File’s Owner) to the

text field.

Establishing a connection from thethe view controller does theequivalent of invokingsetTextField:

on the view controller, passing the text field as the argument.

Now configure the label. Follow the same steps as for the text field, but with appropriate changes to the

configuration.

42 Make Connections2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




To add an outlet from the view controller to the label . . .

● Follow the same steps as for the text field.

In the connection configuration dialog:

● Set the connection type to Outlet.

● Set the name to label.

● Set the type to UILabel.

Make the Text Field’s Delegate Connection

The text field sends a message to its delegate when the user taps the Return button in the keyboard. You

can use this callback to dismiss the keyboard (see “Configure the View Controller as the Text Field’s

Delegate” (page 49)).

To set the text field’s delegate . . .


2. Control-click in the text field.

3. Using the translucent panel that appears, select the open circle after delegate and drag to the File’s

Owner.

Make the Text Field’s Delegate Connection 432011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




Testing

You can now test the application.

To test the application . . .

● Click Run.

Make sure that all the files are saved.

You should find that the button works (it highlights when you tap it). You should also find that if you touchin the text field, the keyboard appears and you enter text. There is, however, no way to dismiss the keyboard.

To do that, you have to implement the relevant delegate method. You’ll do that in the next chapter.

44 Testing2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5




Recap

You configured the nib file with appropriate connections; in doing so, you also updated the header and

implementation files to support the outlets and action.

There’s noneedto use the Xcode feature toaddthe source code at thesametime as establishing a connection;

you canadd thepropertyand method declarations to the header file yourself, and then make theconnections

like you did with the text field’s delegate. Typically, though, you make fewer mistakes (and have less typing

to do) if you let the tools do as much of the work as they can.

Recap 452011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 5





CHAPTER 5




There are several parts to implementing the view controller. You need to add a property for the user’s name

including memory management, implement the changeGreeting:method, and ensure that the keyboard

is dismissed when the user taps Done.

The User’s Name Property

You then need to add a property for the user’s name, which is a string. You add the property declaration to

the view controller’s header file (MyViewController.h).

To add a property declaration for the user’s name . . .

● Add a @property statement for a string called userName.

The property declaration looks like this.

@property (nonatomic, copy) NSString *userName;

Your interface file should look similar to this:


@interface MyViewController : UIViewController <UITextFieldDelegate> {

UITextField *textField;

UILabel *label;

NSString *userName;

}


@property (nonatomic, retain) IBOutlet UILabel *label;



@end

To complete the implementation, you also need to tell the compiler to synthesize the accessor methods, and

update the dealloc method. You add the implementation parts to the view controller’s implementation

file (MyViewController.m).

The User’s Name Property 472011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 6

Implementing the View Controller



To synthesize the accessor methods for user name property . . .

● Synthesize the userName property by adding the following after the @implementation

MyViewController line:

@synthesize userName;

This tells the compiler to synthesize accessor methods for these property according to the specification you

gave in the interface file. The declaration of the userName property is @property (nonatomic, copy)

NSString *userName;), so the compiler generates two accessor methods: - (NSString *)userName

and - (void)setUserName:(NSString *)newUserName. In the setUserName:method a copy is made

of the string that’s passed in. This is useful to ensure encapsulation (the passed-in string might be

mutable—you want to make sure that the controller maintains its own copy). For more about encapsulation,

see “Mechanisms Of Abstraction” in Object-Oriented Programming with Objective-C .

You must relinquish ownership in the dealloc method because the property declaration specifies that the

view controller owns the instance variables (retain and copy imply ownership; see “Memory Management

Rules” in Memory Management Programming Guide).

To correctly handle memory management for the user name property in dealloc . . .

● In the dealloc method, release userName by adding the following before the invocation of super:

[userName release];

The completed dealloc method to should look similar to this:

- (void)dealloc {


[label release];

[userName release];

[super dealloc];

}

The changeGreeting: Method

When a button is tapped, it sends a changeGreeting:message to the view controller. The view controller

then should retrieve the string from the text field and update the label appropriately. Thus, the

changeGreeting: method should:

1. Retrieve the text from the text field and set the controller’s userName property to the result.

2. Create a new string, based on the userName property, to display in the label.

48 The changeGreeting: Method2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 6




To implement the changeGreeting: method . . .

1. In Xcode, display MyViewController.m in the source editor.

2. Complete the implementation of the changeGreeting: method.

- (IBAction)changeGreeting:(id)sender {

self.userName = textField.text;

NSString *nameString = self.userName;

if ([nameString length] == 0) {

nameString = @"World";

}

NSString *greeting = [[NSString alloc] initWithFormat:@"Hello, %@!",

nameString];

label.text = greeting;

[greeting release];

}

There are several new pieces to this method:

● self.userName = textField.text; retrieves the text from the text field and sets the controller’s

userName property to the result.

In this case, you don’t actually use the user name anywhere else, but it ’s important to understand its

role. It’s the very simple model object that the view controller is managing. In general, the controller

should maintain informationabout applicationdata in its ownmodel objects—application datashouldn’t

be stored in user interface elements.

● @"World" is a string constant represented by an instance of NSString.

● The initWithFormat: method creates a new string that follows the format specified by the format

string, like the printf function.

%@ indicatesthat a string object shouldbe substituted. To learn more about strings, seeStringProgramming

Guide.

Configure the View Controller as the Text Field’s Delegate

If you build and run the application, you should findthat if you tap the button, the label shows “Hello, World!”

If you select the text field and start typing, though, you should find that you have no way to indicate that

you’ve finished entering text and dismiss the keyboard.

Configure the View Controller as the Text Field’s Delegate 492011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 6




In an iOS application, the keyboard is shown automatically when an element that allows text entry becomes

the first responder; it is dismissedautomatically when theelement loses first responder status. (You can learn

more about first responder by reading “The Event-Handling System” in iOS Application Programming Guide.)

There’s no way to directly message the keyboard; you can, however, make it appear or disappear as a

side-effect of toggling the first responder status of a text-entry element.

The UITextFieldDelegate protocol includes a method, textFieldShouldReturn:, that the text field

calls whenever the user taps the Return button (whatever text the button shows). Because you set the view

controller as the text field’s delegate, you can implement this method to force the text field to lose first

responder statusbysending it theresignFirstRespondermessage—which has the side-effect of dismissing

the keyboard.

Theview controller must adopt theUITextFieldDelegateprotocol. To specifythata class adopts a protocol,

in the interface add the name of the protocol in angle brackets (<>) after the name of the class from which

your class inherits.

To implement MyViewController as the text field’s delegate . . .

1. In the view controller’s header file (MyViewController.h), add <UITextFieldDelegate> after

UIViewController.

The interface declaration should look like this:


This declaration specifies that the view controller class adopts the UITextFieldDelegate protocol.

2. In the view controller’s implementation file (MyViewController.m), implement the

textFieldShouldReturn:method.

The method should tell the text field to resign first responder status. The implementation might look like this:

- (BOOL)textFieldShouldReturn:(UITextField *)theTextField {

if (theTextField == textField) {

[textField resignFirstResponder];

}

return YES;

}

In this application, it’s not really necessary to include the theTextField == textField test since

there’s only one text field. It’s worth pointing out the pattern, though, since there may be occasions

when your object is the delegate of more than one object of the same type and you may need to

differentiate between them.


Build and run the application; it should behave as you expect. (Tap Done to dismiss the keyboard when you

have entered your name, then tap the Hello button to display “Hello, <Your Name>!” in the label.)

50 Test the Application2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 6




If the application doesn’t behave as you expect, you need to troubleshoot (see “Troubleshooting” (page 53)).

Recap

You finished the implementation of the view controller and so completed your first iOS application.

Congratulations.

Take a moment to think about how the view controller fits into the overall application architecture. You will

use view controllers in all iOS applications you write.

Then take a break, and start to think about what you should do next.

Recap 512011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 6





CHAPTER 6




This section describes some approaches to solving common problems that you may encounter.

Code and Compiler Warnings

If things aren’t working as they should, first compare your code with the complete listings as given in “Code

Listings” (page 59).

Your code should compile without any warnings. Objective-C is a very flexible language, and so sometimes

the most you get from the compiler is a warning. Typically you should treat warnings as very likely to beerrors.

Check the Nib Files

As a developer, if things don’t work correctly, your natural instinct is to check your source for bugs. Cocoa

adds another dimension. Much of your application’s configuration may be “encoded” in the nib files. And if

you haven’t made the correct connections, then your application won’t behave as you expect.

● If your user interface doesn’t reflect changes you made to the nib file, make sure you saved the nib file

before you built the project.

● If the text doesn’t update when you tap the button, it might be that you didn’t connect the button’s

action to the view controller, or connect the view controller’s outlets to the text field or label.

● If the keyboard does not disappear when you tap Done, you may not have connected the text field’s

delegateor connected the view controller’s textFieldoutlet to the text field (see “Makethe Text Field’s

Delegate Connection” (page 43)). If you have connected the delegate, there may be a more subtle

problem (see “Delegate Method Names” (page 53)).

Delegate Method Names

A common mistake with delegates is to misspell the delegate method name. Even if you’ve set the delegate

object correctly, if the delegate doesn’t implement the method with exactly the right name, it won’t be

invoked. It ’s usually best to copy and paste delegate method declarations from the documentation.

Code and Compiler Warnings 532011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 7

Troubleshooting



This chapter suggests directions you might take next in learning about iOS development.

Improve the User Interface

In thistutorial, youcreated a verysimple iOS application. Cocoa Touchoffers a richdevelopment environment,

though, and you’ve only scratched the surface. From here, you should explore further. Start with this

application. As noted in the first chapter, the user interface is critical to a successful iOS application. Try to

improve the user interface. Add images and color to the elements. Add a background image and an icon for

the application. Look at the inspectors in Interface Builder to see how else you can configure elements.

Many iPhone applicationssupport multiple orientations; applications for iPad should support all orientations.

Make sure the view controller supports multiple orientations (see the

shouldAutorotateToInterfaceOrientation:method), then (in Interface Builder) adjust your user

interface to make sure that all the user interface elements are properly positioned if the view is rotated.

Create User Interface Elements Programmatically

In thetutorial, you created the user interface using InterfaceBuilder. InterfaceBuilder allows you to assemble

user interface components quickly and easily. Sometimes, however, you may want—or need—to create userinterface elements in code (for example, if you create a custom table view cell you typically create and lay

out the subviews programmatically).

First, open the MyViewController nib file and remove the text field from view.

If you want to create the entire view hierarchy for a view controller in code, you override loadView. In this

case, however, you want to load the nib file then perform additional configuration (add another view). You

therefore override viewDidLoad instead. (The viewDidLoad method gives you a common override point

you can use whether you load the main view using a nib file or by overriding loadView.)

In MyViewController.m, add the following implementation of viewDidLoad:

- (void)viewDidLoad {

CGRect frame = CGRectMake(20.0, 68.0, 280.0, 31.0);

UITextField *aTextField = [[UITextField alloc] initWithFrame:frame];

self.textField = aTextField;

[aTextField release];

textField.textAlignment = UITextAlignmentCenter;

textField.borderStyle = UITextBorderStyleRoundedRect;

textField.autocapitalizationType = UITextAutocapitalizationTypeWords;

Improve the User Interface 552011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 8

Next Steps



textField.keyboardType = UIKeyboardTypeDefault;

textField.returnKeyType = UIReturnKeyDone;

textField.delegate = self;

[self.view addSubview:textField];

}

Notice that there’s quite a lot of code compared with how easy it was to create and configure the text fieldin Xcode.

In the application delegate, create the view controller instance using alloc and init instead of alloc and

initWithNibName:bundle:

Build and run the application. Make sure it behaves as it did before.

Install the Application on a Device

If you have a suitable device connected to your computer via its 30-pin USB cable, and you have a validcertificate from the iOS Developer Program, set the active SDK for your project to “iPhone Device” (instead

of “iOS Simulator”) and build and run the project. Assuming your code compiles successfully, Xcode then

automatically uploads your application to your device. For more details, see iOS Development Guide.

Add More Functionality

Next you can try expanding on the functionality. There are many directions in which you can go:

● Write a custom view. Rather than using a view as a canvas on which to drop prebuilt user interface

controls, you might try writing a custom view that draws its own content or responds to touch events.

For inspiration, look at examples such as MoveMe and Metronome.

● Use a table view. Although you used Xcode to layout the user interface for this application, many

applications actually use table views to lay out the interface. This makes it easy to create an interface

that extends beyond the bounds of the screen—allowing the user to easily scroll to reveal additional

elements. You should first investigate how to create a simple list using a table view. There are several

sample code projects that you can look at—including TableViewSuite—then you can create your own.

● Use a navigation controller. Navigation controllers and tab bar controllers provide an architecture that

allow you to create drill-down style interfaces and let the user select different views in your application.

Navigation controllers often work in conjunction with table views, but both navigation controllers and

tab bar controllers work together with view controllers. Have a look at some of the sample

applications—such as SimpleDrillDown—that use navigation controllers and expand on them to create

your own applications.

● Localize your app. You can often increase the size of your potential marketplace by localizing your

application. Internationalization is the process of making your application localizable. To learn more

about internationalization, read Internationalization Programming Topics.

● Optimize your code. Performance is critical to good user experience on iOS. You should learn to use

the various performance tools provided with Mac OS X—in particular Instruments—to tune your

application so that it minimizes its resource requirements.

56 Install the Application on a Device2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 8

Next Steps

http://developer.apple.com/iphone/

http://developer.apple.com/iphone/



The most important thing is to try out new ideas and to experiment—there are many code samples you can

look at for inspiration, and the documentation will help you to understand concepts and programming

interfaces.

Add Unit Tests

When you created the project, you didn’t select the option to add support for unit tests. Testing, however,

is an important aspect of best practices for Cocoa development. In some respects you can understand it as

the counterpart of the design principle of encapsulation—it ensures that if the implementation of a method

changes, it still works as advertised. Consider now adding suppor for unit testing. You can either create a

new version of the tutorial that sets up unit testing, or using the current project in Xcode choose File > New

> New Target then select Other > Cocoa Unit Testing Bundle. Look to see what Xcode adds to the project.

To learn about unit testing, see “Unit Testing Applications”.

Add Unit Tests 572011-03-08 | © 2011 Apple Inc. All Rights Reserved.

CHAPTER 8

Next Steps



This appendix provides listings for the two classes you define. The listings don’t show comments and other

method implementations from the file templates.

HelloWorldAppDelegate

The header file: HelloWorldAppDelegate.h



@interface HelloWorldAppDelegate : NSObject <UIApplicationDelegate> {

}

@property (nonatomic, retain) IBOutlet UIWindow *window;


@end

The implementation file: HelloWorldAppDelegate.m#import "MyViewController.h"

#import "HelloWorldAppDelegate.h"

@implementation HelloWorldAppDelegate

@synthesize window=_window;


- (BOOL)application:(UIApplication *)application

didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

MyViewController *aViewController = [[MyViewController alloc]initWithNibName:@"MyViewController" bundle:[NSBundle mainBundle]];




[self.window makeKeyAndVisible];

return YES;

}

HelloWorldAppDelegate 592011-03-08 | © 2011 Apple Inc. All Rights Reserved.

APPENDIX A

Code Listings



// Other methods from the template omitted

- (void)dealloc {


[_window release];

[super dealloc];}

@end

MyViewController

The header file: MyViewController.h



UITextField *textField;

UILabel *label;

NSString *userName;

}


@property (nonatomic, retain) IBOutlet UILabel *label;



@end

The implementation file: MyViewController.m


@implementation MyViewController

@synthesize textField;

@synthesize label;

@synthesize userName;

- (BOOL)textFieldShouldReturn:(UITextField *)theTextField {

if (theTextField == textField) {

[textField resignFirstResponder];

}

return YES;

}

- (void)dealloc {


[label release];

60 MyViewController2011-03-08 | © 2011 Apple Inc. All Rights Reserved.

APPENDIX A

Code Listings



[userName release];

[super dealloc];

}

- (IBAction)changeGreeting:(id)sender {

self.userName = textField.text;

NSString *nameString = self.userName;

if ([nameString length] == 0) {

nameString = @"World";

}

NSString *greeting = [[NSString alloc] initWithFormat:@"Hello, %@!",

nameString];

label.text = greeting;

[greeting release];

}

// Other methods from the template omitted.

@end

MyViewController 612011-03-08 | © 2011 Apple Inc. All Rights Reserved.

APPENDIX A

Code Listings



This table describes the changes to Your First iOS Application.

NotesDate

Updated for Xcode 4.2011-03-08

Corrected a bad link.2010-10-12

Updated for iOS 4.2010-07-01

Updated for iOS 3.2.2010-03-15

Emphasized need to connect text field in Interface Builder.2009-10-08

Removed a reference todotsyntax for an example that used an accessor method

directly.

2009-08-10

Updated for iOS 3.0.2009-06-15

Corrected typographical errors.2009-01-06

Clarified description of the target-action design pattern.2008-10-15

Minor corrections and clarifications.2008-09-09

New document that introduces application development for iPhone.2008-06-09


REVISION HISTORY

Document Revision History



REVISION HISTORY

Document Revision History

00-your first iphone os application

Documents