@protocol Declaration <NSObject>
@optional
-(void)background;                                          // Создание делегата
@end
@property (nonatomic,weak) id <Declaration> delegate;

 if ([self.delegate respondsToSelector:@selector(background)]){
        [self.delegate background];                                 // Проверка "доставки делегата"
    }

 [self background];
    ViewController * maincon = [[ViewController alloc] init];
    maincon.delegate = self;
}
-(void)background {
    NSLog(@"Great");

}