Example of how to add properties to categories (Thank you: http://www.davidhamrick.com/2012/02/12/Adding-Properties-to-an-Objective-C-Category.html)

gistfile1.m

//  THGridMenuItem+ProjectItem.h
#import "THGridMenuItem.h"
#import "Project.h"

@interface THGridMenuItem (ProjectItem)

@property (nonatomic, strong) Project *project;

-(Project *)project;
-(void)setProject:(Project *)project;

@end

//  THGridMenuItem+ProjectItem.m

#import "THGridMenuItem+ProjectItem.h"
#import <objc/runtime.h>

static char projectMenuItemKey;

@implementation THGridMenuItem (ProjectItem)

-(Project *)project {
    return objc_getAssociatedObject(self, &projectMenuItemKey);
}

-(void)setProject:(Project *)project {
    objc_setAssociatedObject(self, &projectMenuItemKey, project, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}



@end