A simple category which adds a familiar method (UIAlertView) for showing a UIAlertController instance from anywhere in your iOS project.

UIAlertController+Show.h

#import <UIKit/UIKit.h>

@interface UIAlertController (Show)

-(void)show;

-(void)showWithCompletion:(void(^)())completion;

-(void)showWithCompletion:(void(^)())completion failure:(void(^)())failure;

@end

UIAlertController+Show.m

#import "UIAlertController+Show.h"

@implementation UIAlertController (Show)

-(void)show
{
	[self showWithCompletion:nil];
}

-(void)showWithCompletion:(void(^)())completion
{
	[self showWithCompletion:completion failure:nil];
}

-(void)showWithCompletion:(void(^)())completion failure:(void(^)())failure
{
	UIViewController *viewController = [self topMostViewController];
	
	if (viewController)
	{
		[viewController presentViewController:self animated:YES completion:completion];
	}
	else
	{
		if (failure)
		{
			failure();
		}
		else
		{
			NSLog(@"ERROR: Could not find a viewController to present from!");
		}
	}
}

#pragma mark - Internal

-(UIViewController*)topMostViewController
{
	UIViewController *viewController = [[[UIApplication sharedApplication] keyWindow] rootViewController];
	
	if (viewController)
	{
		while (viewController.presentedViewController)
		{
			viewController = viewController.presentedViewController;
		}
	}
	
	if (viewController.isBeingDismissed || viewController.isBeingPresented || viewController.isMovingFromParentViewController || viewController.isMovingToParentViewController)
	{
		return nil;
	}
	
	return viewController;
}

@end