CODEWITHSUNDEEP
objective-cprotocols
Rephisto
Rephisto

Reputation: 89

how to solve 2 protocols which both of them have a reference to other one

I am trying to create several protocols, and most of them have references to other ones. But I get error during the build process.

I give an example:

#import <Foundation/Foundation.h>

@protocol DataChildDelegate <NSObject>

@property(nonatomic) id<DataParentDelegate> parent;

@end

@protocol DataParentDelegate <NSObject>

@property(nonatomic) id<DataChildDelegate> firstChild;
@property(nonatomic) id<DataChildDelegate> lastChild;

@end

I tried to divide DataChildDelegate in two parts like this:

#import <Foundation/Foundation.h>

@protocol DataChildDelegate <NSObject>
@end

@protocol DataParentDelegate <NSObject>

@property(nonatomic) id<DataChildDelegate> firstChild;
@property(nonatomic) id<DataChildDelegate> lastChild;

@end

@protocol DataChildDelegate <NSObject>

@property(nonatomic) id<DataParentDelegate> parent;

@end

But this time I get a warning.

Is there any more suitable way to handle this problem?

Thanks

Upvotes: 1

Views: 61

Answers (1)

wmorrison365
wmorrison365

Reputation: 6318

You should use a forward declaration of the protocol DataChildDelegate prior to DataParentDelegate so that the compiler can trust that it exists.

For example:

#import <Foundation/Foundation.h>

@protocol DataChildDelegate;     /*Forward declaration of DataChildDelegate */

@protocol DataParentDelegate <NSObject>

@property(nonatomic) id<DataChildDelegate> firstChild;
@property(nonatomic) id<DataChildDelegate> lastChild;

@end

@protocol DataChildDelegate <NSObject>

@property(nonatomic) id<DataParentDelegate> parent;

@end

Upvotes: 2

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