In this tutorial, little regard is given to the user interface. Presentation is, however, a critical component of a
successful iPhone OS application. You should read the iPhone Human Interface Guidelines and explore the
sample code based on this tutorial (HelloWorld) to understand how the user interface might be improved
for a full-fledged application.
You’ll also start to gain an understanding of how view controllers work and how they fit into the architecture
of an iPhone OS application.
Design Patterns
If you haven’t already, you should make sure you read the design patterns chapter in Cocoa Fundamentals
Guide, however the main patterns you’re going to use 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 where one object periodically sends messages to another object specified as its
delegate to ask for input or to notify the delegate that an event is occurring. You 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 are typically grouped together into a protocol. A protocol is basically just a list of methods.
If a class conforms to 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 Rockets in a game, ToDo items and Contacts in a
productivity application, or Circles and Squares in a drawing application.
In this application, the model is very simple—just a string—and it’s not actually used outside of a single
method, so strictly speaking 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.
10
Design Patterns
2010-03-15 | © 2010 Apple Inc. All Rights Reserved.
CHAPTER 1
Tutorial Overview and Design Patterns
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