UINavigationController custom navigation bar

MyAppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.

    // Create a new window and assign directly to provided iVar
    _window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    
    // Implementation of new init method
    MyCustomNavigationBar *navigationBar = [[MyCustomNavigationBar alloc] initWithFrame:CGRectZero];
    UINavigationController *navigationController = [[UINavigationController alloc] initWithCustomNavigationBar:navigationBar];
    [navigationBar release];
    
    [self.window setRootViewController:navigationController];
    [navigationController release];

    [self.window makeKeyAndVisible];
    return YES;
}

UINavigationController-CustomNavigationBar.h

#import <UIKit/UIKit.h>

@interface UINavigationController (MTCustomNavigationBar)

- (id)initWithCustomNavigationBar:(UINavigationBar *)navigationBar;

@end

UINavigationController-CustomNavigationBar.m

#import "UINavigationController-MTCustomNavigationBar.h"
#import <objc/runtime.h>

@implementation UINavigationController (MTCustomNavigationBar)

- (id)initWithCustomNavigationBar:(UINavigationBar *)navigationBar
{
    self = [self initWithNibName:nil bundle:nil];
    
    if (self)
    {
        // Init

        // Verify subclasses parent class is UINavigationBar
        if (navigationBar != nil && [navigationBar isKindOfClass:[UINavigationBar class]])
        {
            UINavigationBar *navigationBar__ = nil;
            
            // Get the unexposed ivar for navigation bar replacement
            Ivar ivar_navigationBar__ = object_getInstanceVariable(self, "_navigationBar", (void **)&navigationBar__);
            
            // Clean up memory if a navigation bar has already been assigned
            if (navigationBar__ != nil)
                [navigationBar__ release];
            
            // Assign the custom navigation bar to the retrieved ivar
            navigationBar__ = [navigationBar retain];
            object_setIvar(self, ivar_navigationBar__, navigationBar__);   
        }
    }
    
    return self;
}

@end