UINavigationController+CompletionHandler.h

  //
//  UINavigationController+CompletionHandler.h
//  Entire
//
//  Created by ChristianEnevoldsen on 10/08/14.
//  Copyright (c) 2014 Reversebox. All rights reserved.
//
//  Forked by Dario Carlomagno on 03/10/14.
//  Copyright (c) 2014 Monksoftware. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UINavigationController (CompletionHandler)

- (void)pushViewController:(UIViewController *)viewController
                  animated:(BOOL)animated
                completion:(void (^)(void))completion;

- (void)popViewController:(UIViewController *)viewController
                 animated:(BOOL)animated
                completion:(void (^)(void))completion;

- (void)popToRootViewControllerAnimated:(BOOL)animated
                             completion:(void (^)(void))completion;

@end

UINavigationController+CompletionHandler.m

//
//  UINavigationController+CompletionHandler.m
//  Entire
//
//  Created by ChristianEnevoldsen on 10/08/14.
//  Copyright (c) 2014 Reversebox. All rights reserved.
//
//  Forked by Dario Carlomagno on 03/10/14.
//  Copyright (c) 2014 Monksoftware. All rights reserved.
//

#import "UINavigationController+CompletionHandler.h"
#import <QuartzCore/QuartzCore.h>

@implementation UINavigationController (CompletionHandler)
- (void)pushViewController:(UIViewController *)viewController
                  animated:(BOOL)animated
                completion:(void (^)(void))completion
{
    [CATransaction begin];
    [CATransaction setCompletionBlock:completion];
    [self pushViewController:viewController animated:animated];
    [CATransaction commit];
}

- (void)popViewController:(UIViewController *)viewController
                 animated:(BOOL)animated
               completion:(void (^)(void))completion
{
    [CATransaction begin];
    [CATransaction setCompletionBlock:completion];
    [self popViewController:[self backViewController] animated:animated];
    [CATransaction commit];
}

- (void)popToRootViewControllerAnimated:(BOOL)animated
                             completion:(void (^)(void))completion
    [CATransaction begin];
    [CATransaction setCompletionBlock:completion];
    [self popToRootViewControllerAnimated:animated];
    [CATransaction commit];
}

- (UIViewController *)backViewController
{
    NSInteger numberOfViewControllers = self.viewControllers.count;
    
    if (numberOfViewControllers < 2)
        return nil;
    else
        return [self.navigationController.viewControllers objectAtIndex:numberOfViewControllers - 2];
}

@end