What exactly are protocols and delegates and how are they used in IOS?

Question

I\'m really confused about the concept of delegates and protocols. Are they equivalent of interfaces and adapter classes in Java? How do they work? None of the resources I\

Answer 1

In it's simplest form a delegate is an object which receives messages from another object. And you do it all the time.

So say you had car object with an engine.

@interface car : NSObject

@property (nonatomic) id engine;

@end

So could forward a start message to the engine.

[_engine start];

The engine is acting as a delegate, you're just passing it a message.

Protocols make it more formal, and Xcode will check that you are conforming to the required or optional methods.

@property (nonatomic) id  engine;

says that the engine object MUST contain the function start because in the the protocol definition it asked for it.

@protocol engineDelegate 
 - (void) start;
@optional
 - (double) fuelLevel;
@end

Why are delegates and protocols so cool? Well because the engine could be any number of different engines which you could use at runtime, it could be a jet engine, a combustion engine, a phasing modulating engine it doesn't matter, as long as it conforms to the protocol. And you tell Xcode that it does conform by adding the delegate to the class interface.

@interface timeWarpDrive : NSObject