BaseNavigationController.h

@interface BaseNavigationController : UINavigationController

- (id)initWithRootViewController:(UIViewController *)rootViewController navigationBarBackgroundImage:(UIImage *)backgroundImage;

@end

BaseNavigationController.m

#import "BaseNavigationController.h"
#import <objc/runtime.h>
#import <objc/message.h>

static const void *kNavigationBarBackgroundImageAssociatedObjectKey = "kNavigationBarBackgroundImageAssociatedObjectKey";

@interface BaseNavigationBar : UINavigationBar
@end

@implementation BaseNavigationController

- (void)dealloc {
    [super dealloc];
}

- (id)initWithRootViewController:(UIViewController *)rootViewController {
    return [self initWithRootViewController:rootViewController navigationBarBackgroundImage:nil];
}

- (id)initWithRootViewController:(UIViewController *)rootViewController navigationBarBackgroundImage:(UIImage *)backgroundImage {
    self = [super initWithRootViewController:rootViewController];
    if (backgroundImage) {
        if ([self.navigationBar respondsToSelector:@selector(setBackgroundImage:forBarMetrics:)]) {
            [self.navigationBar setBackgroundImage:backgroundImage forBarMetrics:UIBarMetricsDefault];
        } else {
            object_setClass(self.navigationBar, [BaseNavigationBar class]);
            objc_setAssociatedObject(self.navigationBar, kNavigationBarBackgroundImageAssociatedObjectKey, backgroundImage, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        }
    }

    return self;
}

@end

@implementation BaseNavigationBar

- (void)dealloc {
    objc_removeAssociatedObjects(self);
    [super dealloc];
}

- (void)drawRect:(CGRect)rect {
    UIImage *backgroundImage = objc_getAssociatedObject(self, kNavigationBarBackgroundImageAssociatedObjectKey);
    if (backgroundImage) {
        [backgroundImage drawInRect:self.bounds];
    } else {
        [super drawRect:rect];
    }
}

@end

RootNavigationController.h

#import "BaseNavigationController.h"

@interface RootNavigationController : BaseNavigationController

@end

RootNavigationController.m

#import "RootNavigationController.h"

@implementation RootNavigationController

- (void)dealloc {    
    [super dealloc];
}

- (id)initWithRootViewController:(UIViewController *)rootViewController {
    return [super initWithRootViewController:rootViewController navigationBarBackgroundImage:[UIImage imageNamed:@"RootNavigationBarBackground.png"]];
}

@end