4-4报错

//Protocol.h

#import <Foundation/Foundation.h>

@protocol MyDelegate;

@interface Protocol : NSObject

@property(nonatomic,weak) id<MyDelegate> delegate;

-(void)myPrint;

@end

@protocol MyDelegate <NSObject>

@optional

-(void)print;

@end

//Protocol.m

#import "Protocol.h"

@implementation Protocol

-(void)myPrint{

    if([self.delegate respondsToSelector:@selector(print)]){

        [self.delegate print];

    }

}

@end

//Delegate.h

#import <Foundation/Foundation.h>

#import "Protocol.h"

@interface Delegate : NSObject <MyDelegate>

-(void)testDelegate;

@end

//Delegate.m

#import "Delegate.h"

@implementation Delegate

-(void)testDelegate{

    Protocol *p = [[Protocol alloc]init];

    p.delegate = self;

    [p myPrint];

}

-(void)print{

    NSLog(@"你有一条消息，请查收");

}

@end

//main.m

#import <Foundation/Foundation.h>

#import "Delegate.h"

int main(int argc, const char * argv[]) {

    @autoreleasepool {

        Delegate *d = [[Delegate alloc]init];

        [d testDelegate];

    }

    return 0;

}