เวลาจะใช้ก็แค่เรียก [[DelegateHelper sharedInstance].delegate delegateHelperSomething]; จบข่าว

DelegateHelper.h

#import <Foundation/Foundation.h>

@class DelegateHelper;
@protocol DelegateHelperDelegate <NSObject>

- (void) delegateHelperSomething;

@end

@interface DelegateHelper : NSObject

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

+ (DelegateHelper*)sharedInstance;

@end

DelegateHelper.m

#import "DelegateHelper.h"

@implementation DelegateHelper

+ (DelegateHelper*)sharedInstance
{
    static dispatch_once_t pred = 0;
    __strong static id _sharedObject = nil;
    
    dispatch_once(&pred, ^{
        NSLog(@"DataService: dispatch op");
        _sharedObject = [[self alloc] init]; // or some other init method
        
    });
    return _sharedObject;
}

@end