Receiver type () for instance message is a forward declaration issue in ARC

Question

I have two protocols BaseDAO, and ICategoryDAO. ICategoryDAO adopt BaseDao. Class categoryDao adopt ICategoryDao.

The below code is the initializer method of serviceRepo class (sub class of NSObject). Here I perform the type check and etc.

 - (id)init {
        self = [super init];
        if (self) {
            self.dict  = [NSMutableDictionary new];
            [self.dict setValue:[CategoryDao description] forKey:[NSString stringWithFormat:@"%s",[@protocol(ICategoryDao) name]]];
        }
        return self;
    }

the problem is Xcode always pop the error Receiver type 'Protocol' for instance message is a forward declaration in this call -> [@protocol(ICategoryDao) name]. Im using ARC, it works fine on non ARC project. I couldn't find any solution in the internet, so finally Im here. How can I solve this issue, am I doing anything wrong here.

This is the structure of the protocols and classes;

BaseDao

#import <Foundation/Foundation.h>

@protocol BaseDao <NSObject>

ICategoryDAO

#import <Foundation/Foundation.h>
#import "BaseDao.h"

@protocol ICategoryDao <BaseDao>

CategoryDAO

#import <Foundation/Foundation.h>
#import "ICategoryDao.h"

@interface CategoryDao : NSObject <ICategoryDao>

ServiceRepo

#import <Foundation/Foundation.h>

@interface ServiceRepository : NSObject

ServiceRepo.m

#import "ServiceRepository.h"
#import "CategoryDao.h"
#import "BaseDao.h"

@implementation ServiceRepository

Usually an error like this means, that you need to import the .h file. So you could try importing the ICategoryDao.h directly in the SeviceRepo.m. Maybe that helps. — Tobi
Out of curiosity i've never seen sth. like [@protocol(ICategoryDao) name]. What does the @protocol() do here? — Tobi
[@protocol(ICategoryDao) name] name is the method of iCategoryDao protocol right? — Pandey_Laxman
i just want to store the name of the protocol as the key in the dictionary. @Pandey no it is not. name method return nsstring object used to uniquely identify the receiver . is there any other way, I can use to store the name of the protocol as key in the dict. — Clement Prem

Pandey_Laxman Pandey_Laxman · Accepted Answer · 2012-10-23T07:38:59

Please try below code that might help you.

[self.dict setValue:[CategoryDao description] forKey:[NSString stringWithFormat:@"%s",NSStringFromProtocol(@protocol(ICategoryDao))];

NSProtocolFromString Returns a the protocol with a given name.

Protocol *NSProtocolFromString (
   NSString *namestr
);

Parameters

namestr The name of a protocol.

Return Value

The protocol object named by namestr, or nil if no protocol by that name is currently loaded. If namestr is nil, returns nil.

Receiver type () for instance message is a forward declaration issue in ARC

1 Answers