What Does "Delegate" Mean in Xcode?

A delegate is a helper class in Cocoa.

You can use the Xcode integrated development environment from Apple to program iPhone, iPod touch and iPad apps in the Objective-C and Cocoa programming languages. Cocoa is the application programming interface, which lets you connect to iPhone, iPod touch and iPad services such as a map or camera. A delegate is a helper class in Cocoa that enables another object to notify it when certain events happen.

Role of Delegate

The delegate receives messages from a host object that contains a pointer reference to the delegate. The object sends messages to the delegate when it needs its input for a task.

Why Delegates Needed

The object needs the delegate because the object can only accomplish a generic task, so it needs the delegate to accomplish a more specific task.

How Delegation Works

The object notifies the delegate when the object needs its input for a particular task. The delegate provides specific behavior at various points in the task.

Delegation Design Pattern

Delegation is common in Cocoa. It is best practice to use delegation rather than subclassing a class.

References

• iPhone Developer Tips: The Basics of Protocols and Delegates
• How to create our own delegate for any class in iPhone?
• iPhone Dev SDK: Understanding Delegates
• Apple: Cocoa Design Patterns

Resources

• Apple: The Objective C Programming Language
• Apple: What is Cocoa?