Categoryで擬似インスタンス変数を設定する

UIViewController+MyCategory.h

#import <UIKit/UIKit.h>

@interface UIViewController (MyCategory)

@property (nonatomic, strong) NSNumber *myProperty;

@end

UIViewController+MyCategory.m

#import "UIViewController+MyCategory.h"
#import <objc/runtime.h>

static char myPropertyKey;

@implementation UIViewController (MyCategory)

- (void)setMyProperty:(NSNumber *)myProperty
{
    objc_setAssociatedObject(self, &myPropertyKey, myProperty, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSNumber *)myProperty
{
    return objc_getAssociatedObject(self, &myPropertyKey);
}

@end