AppDelegate accesible de forma global

AppDelegate.h

#import <UIKit/UIKit.h>

#define ApplicationDelegate ((QBKAppDelegate *)[UIApplication sharedApplication].delegate)

@interface QBKAppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;
@property (copy, nonatomic) NSString* unaCadena;

@end

otroArchivo.m

NSString* unString = ApplicationDelegate.unaCadena;