Question

I am new to objective-c and pretty much confused with the way delegates are used. I came across this code and i would like to use it to clarify some of the doubts.

#import <Foundation/Foundation.h>

@protocol ProcessDataDelegate <NSObject>

@required
- (void) processSuccessful: (BOOL)success;

@end

@interface ClassWithProtocol : NSObject 
{
  id <ProcessDataDelegate> delegate;
}

@property (retain) id delegate;

 -(void)startSomeProcess;

@end

Here, there are 2 references to the word “delegate” can anyone explain what it means when used in context with “id angled bracket delegate angled-bracket-closed” ??

Again, there is a property with name delegate. Should it not cause any kind of conflict ??

Thanks in advance,

Answer 1

Nope, there is just one property, the one defined by @property (retain) id delegate; the other one is (sort of) private variable of the NSObject which is not a property in a objective-c sense… then, you have @synthetize keyword in your .m file, which expands the property.

The other notation, id<protocol> is telling, that delegate is expected to conform to a certain protocol.

You can access both from the class, but you can access only property from outside. Also, for a property, some other stuff is generated – in case of retain (when not using ARC), memory management routines.

To complete the (confusion?) lecture, there is a nice way to have class private properties, when you define them in .m file instead of .h in an anonymous category like:

@interface MyClass()

@property (nonatomic, retain) NSString privateString;

@end

@implementation
@synthetize privateString;

// ...

@end