iOS change previous button globally

UIViewController+BackButton.h

#import "UIViewController+BackButton.h"
#import <objc/runtime.h>

@implementation UIViewController (PMTBackButton)

+(void)load
{
	Method viewWillAppear = class_getInstanceMethod(self, @selector(customViewWillAppear:));

	Method customViewWillAppear = class_getInstanceMethod(self, @selector(viewWillAppear:));
	method_exchangeImplementations(viewWillAppear, customViewWillAppear);
}

-(void)customViewWillAppear:(BOOL)animated{
	[self customViewWillAppear:animated];
	if ([self.navigationController.viewControllers indexOfObject:self] != 0  && !self.navigationItem.hidesBackButton){

		UIBarButtonItem *previousBarButton = nil;

		UIButton* previousButton = [UIButton buttonWithType:UIButtonTypeCustom];
		[previousButton addTarget:self action:@selector(popViewControllerWithAnimation) forControlEvents:UIControlEventTouchUpInside];
		[previousButton setImage:[UIImage imageNamed:@"back_btn.png"] forState:UIControlStateNormal];
		previousButton.frame = CGRectMake(0, 0, 20, 20);
//		[cancelButton sizeButtonToFit];

		previousBarButton = [[UIBarButtonItem alloc] initWithCustomView:previousButton];

		NSMutableArray * leftButtons = [NSMutableArray arrayWithObject:previousBarButton];
		[leftButtons addObjectsFromArray:self.navigationItem.leftBarButtonItems];
		[self.navigationItem setLeftBarButtonItem:nil];
		[self.navigationItem setLeftBarButtonItems:leftButtons];
	}

	[self.navigationItem setHidesBackButton:YES];
}

-(void)popViewControllerWithAnimation{
	[self.navigationController popViewControllerAnimated:YES];
}
@endb