Objective-c on the protocol defined a property protocol

Question

I read some code, I founded the @protocol have defined a @property's protocol.

For example

protocol1.h

@protocol protocol2;
@protocol protocol1

-(void)p1_method1;
-(void)p1_method2;

@property (readonly, nonatomic) id<protocol2>p2;

@end

protocol2.h

@protocol protocol2

-(void)p2_method1;
-(void)p2_method2;

@end

I don't know the protocol have a @property protocol mean. Have a simple example? Thanks.

You might be interested in this: http://stackoverflow.com/questions/11746986/ios-how-to-implement-a-protocols-property?lq=1 — mttrb, Dec 02 '13 at 10:42

score 1 · Answer 1 · answered Dec 02 '13 at 10:32

You have to add protocol above the interface you will be using.

@protocol MyViewControllerDelegate;

@interface MyViewController : UIViewController

@property (weak, nonatomic) id <MyViewControllerDelegate> delegate;
@property (copy, nonatomic) NSArray *viewControllers;
@end

@protocol MyViewControllerDelegate <NSObject>

@optional

//sth
@end

score 0 · Accepted Answer · answered Dec 02 '13 at 11:11

All you need to do is @synthesize p2 in a class that conforms to protocol1. Properties from protocols don't get automatically synthesised.

@interface Class1 : NSObject <protocol1>

@end

@implementation Class1

@synthesize p2;      // Synthesize p2, the property from protocol1

- (void)p1_method1 {
    // Do something    
}

- (void)p1_method2 {
    // Do something else
}

This will create the correct getter/setter for the property (in your example the property is readonly so only a getter). The @synthesize will also create the ivar, in this case p2.

Objective-c on the protocol defined a property protocol

2 Answers2