Question

I have a protocol like this:

#import <Foundation/Foundation.h>

@protocol Prot1 <NSObject>

@required
- (void)methodInProtocol;

@end

This is a protocol for a delegate I want to store in a class like this:

#import <Cocoa/Cocoa.h>

@class Prot1;

@interface Class1 : NSObject

@property (nonatomic, strong) Prot1 *delegate;

- (void)methodInClass;

@end

The implementation for this class is like this:

#import "Class1.h"
#import "Prot1.h"

@implementation Class1

@synthesize delegate;

- (void)methodInClass {
    [delegate methodInProt];
}

@end

When I build these pieces of code, I get the following error:

Receiver type 'Prot1' for instance message is a forward declaration

What is wrong here? I did understand that I have to do a forward declaration via @class for the protocol and I thought I only had to #import the protocol, in the class implementation… Isn’t that right?

Answer 1

As it isnt a class, you have to define it as what it is – a protocol 😉

Use forward declaration: @protocol Prot1;;

And use the property like that:
@property (nonatomic, strong) id<Prot1> delegate;