title: iOS: Is there currently a way to prevent two view controllers being pushed or popped at the same time?
body: <p>The only solution I have seen was an answer to a stackoverflow question. I posted the link below. The answer I am referring is the 5th one.  It seems that some users have some problems with the solution however. I don't know if there is another category to prevent two controllers from being pushed at the same time. Any tips or suggestions are appreciated.</p>
  
  <pre><code>#import "UINavigationController+Consistent.h"
  #import &lt;objc/runtime.h&gt;
  /// This char is used to add storage for the isPushingViewController property.
   static char const * const ObjectTagKey = "ObjectTag";
  
   @interface UINavigationController ()
   @property (readwrite,getter = isViewTransitionInProgress) BOOL viewTransitionInProgress;
  
   @end
  
  @implementation UINavigationController (Consistent)
  
  - (void)setViewTransitionInProgress:(BOOL)property {
  NSNumber *number = [NSNumber numberWithBool:property];
  objc_setAssociatedObject(self, ObjectTagKey, number , OBJC_ASSOCIATION_RETAIN);
  }
  
  
  - (BOOL)isViewTransitionInProgress {
  NSNumber *number = objc_getAssociatedObject(self, ObjectTagKey);
  
  return [number boolValue];
  }
  
  
   #pragma mark - Intercept Pop, Push, PopToRootVC
   /// @name Intercept Pop, Push, PopToRootVC
  
   - (NSArray *)safePopToRootViewControllerAnimated:(BOOL)animated {
  if (self.viewTransitionInProgress) return nil;
  if (animated) {
      self.viewTransitionInProgress = YES;
  }
  //-- This is not a recursion, due to method swizzling the call below calls the original  method.
  return [self safePopToRootViewControllerAnimated:animated];
  
   }
  
  
    - (NSArray *)safePopToViewController:(UIViewController *)viewController animated:(BOOL)animated {
  if (self.viewTransitionInProgress) return nil;
  if (animated) {
      self.viewTransitionInProgress = YES;
     }
  //-- This is not a recursion, due to method swizzling the call below calls the original  method.
  return [self safePopToViewController:viewController animated:animated];
     }
  
  
   - (UIViewController *)safePopViewControllerAnimated:(BOOL)animated {
  if (self.viewTransitionInProgress) return nil;
  if (animated) {
      self.viewTransitionInProgress = YES;
  }
  //-- This is not a recursion, due to method swizzling the call below calls the original  method.
  return [self safePopViewControllerAnimated:animated];
   }
  
  
  
    - (void)safePushViewController:(UIViewController *)viewController animated:(BOOL)animated {
  self.delegate = self;
  //-- If we are already pushing a view controller, we dont push another one.
  if (self.isViewTransitionInProgress == NO) {
      //-- This is not a recursion, due to method swizzling the call below calls the original  method.
      [self safePushViewController:viewController animated:animated];
      if (animated) {
          self.viewTransitionInProgress = YES;
      }
      }
      }
  
  
  // This is confirmed to be App Store safe.
  // If you feel uncomfortable to use Private API, you could also use the delegate method navigationController:didShowViewController:animated:.
  - (void)safeDidShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
  //-- This is not a recursion. Due to method swizzling this is calling the original method.
  [self safeDidShowViewController:viewController animated:animated];
  self.viewTransitionInProgress = NO;
   }
  
  
  // If the user doesnt complete the swipe-to-go-back gesture, we need to intercept it and set the flag to NO again.
   - (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
  id&lt;UIViewControllerTransitionCoordinator&gt; tc = navigationController.topViewController.transitionCoordinator;
  [tc notifyWhenInteractionEndsUsingBlock:^(id&lt;UIViewControllerTransitionCoordinatorContext&gt; context) {
      self.viewTransitionInProgress = NO;
      //--Reenable swipe back gesture.
      self.interactivePopGestureRecognizer.delegate = (id&lt;UIGestureRecognizerDelegate&gt;)viewController;
      [self.interactivePopGestureRecognizer setEnabled:YES];
  }];
  //-- Method swizzling wont work in the case of a delegate so:
  //-- forward this method to the original delegate if there is one different than ourselves.
  if (navigationController.delegate != self) {
      [navigationController.delegate navigationController:navigationController
                                   willShowViewController:viewController
                                                 animated:animated];
  }
  }
  
  
    + (void)load {
  //-- Exchange the original implementation with our custom one.
  method_exchangeImplementations(class_getInstanceMethod(self,  @selector(pushViewController:animated:)), class_getInstanceMethod(self, @selector(safePushViewController:animated:)));
  method_exchangeImplementations(class_getInstanceMethod(self, @selector(didShowViewController:animated:)), class_getInstanceMethod(self, @selector(safeDidShowViewController:animated:)));
  method_exchangeImplementations(class_getInstanceMethod(self, @selector(popViewControllerAnimated:)), class_getInstanceMethod(self, @selector(safePopViewControllerAnimated:)));
  method_exchangeImplementations(class_getInstanceMethod(self, @selector(popToRootViewControllerAnimated:)), class_getInstanceMethod(self, @selector(safePopToRootViewControllerAnimated:)));
  method_exchangeImplementations(class_getInstanceMethod(self, @selector(popToViewController:animated:)), class_getInstanceMethod(self, @selector(safePopToViewController:animated:)));
   }
  
   @end
  </code></pre>
  
  <p><a href="https://stackoverflow.com/questions/19560198/ios-app-error-cant-add-self-as-subview">iOS app error - Can&#39;t add self as subview</a></p>