back swipe gesture in UINavigationController on iOS 7

// enable

    if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {

        self.navigationController.interactivePopGestureRecognizer.delegate = nil;

}

// disable

    if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {

        self.navigationController.interactivePopGestureRecognizer.enabled = NO;

}