Understanding the Navigation Stack

This morning I wrote about a bug in Corgi Corral that I’d been dealing with for a few months. The act of writing about it was apparently just what my brain needed in order to sort it out, and as it happens, it was a real rookie mistake! I’m hoping that by explaining the problem (and solution), I might help other beginners like me.

I started my previous post by explaining Corgi Corral’s navigation stack:

Main Menu –> Scene Selection –> GameViewController –> Score Summary

Basically, the game’s view controllers should always be in that order. From the main menu, you progress to a level selection screen, then to the game itself, and finally to a summary of your score. From there, you should only move backwards through the stack. In other words, the “retry level” button should pop the score summary off the stack and move back down to the game controller. The “choose a different level” button should pop two view controllers off the stack and go all the way back to the Scene Selection screen.

Here’s where I went wrong: in my Storyboard, on the Score Summary screen, I accidentally hooked up the “choose a different level” button to a “Show” segue instead of an “unwind” segue. This caused the following to happen:

Main Menu -> Scene Selection -> GameViewController -> Score Summary -> Scene Selection

In other words, a brand new “Scene Selection” controller was pushed onto the stack. The problem was compounded each time I selected a new level:

Main Menu -> Scene Selection -> GameViewController -> Score Summary -> Scene Selection -> GameViewController -> Score Summary -> Scene Selection -> GameViewController

You can see how after playing a few games, this got way out of hand. There were multiple GameViewControllers in existence that still had references to game scenes. The memory growth, however, was somehow still negligible despite all of these duplicates.

So how did I diagnose the problem? By using simple print debugging. In the viewWillAppear method of each view controller I printed out the entire navigation stack like so: print(navigationController.viewControllers). Then I watched the output as I played a few games. As soon as I saw new controllers being added to the stack, I knew I was in trouble.

The solution was to make sure I was using an unwind segue to move backwards through the stack after the user selected an option from the Score Summary screen.

I know, I know…dumbest mistake ever. But now at least I know that there will only ever be four view controllers in existence at one time in my app. I hope someone can learn from this!

January 25th – Progress Update

It’s been a week since I last blogged; here’s what I’ve been up to!


  1. I created some art assets for the second level/scene, which has an autumnal theme. The screenshot below shows a funny bug (now fixed) in which a sheep would spawn in the wheelbarrow and be unable to escape.

    Corgi Corral Level 2

  2. The corgi now blinks when idle and barks occasionally during the game.
  3. I created a struct called “LevelConfiguration” that reads information from a property list. The list contains information like how many animals should spawn, what the time limit should be, what sounds should be used, etc.
  4. For scene management, I decided to abandon the idea of a SpriteKit-only solution and ran back to something I’m more familiar with: UIKit and Storyboards. I set up bare-bones view controllers with simple UIButtons and UILabels that players can use to navigate to and from the main menu, options screen, etc. They’re not pretty, but they work, and now all I have to do is create art assets for them:

    Storyboard Layout

  5. After the timer for a level runs out, the game now waits 3 seconds and displays a score summary screen with options to retry the level, select a different level, or return to the main menu.

Under Consideration

Here are a couple of things I’m mulling over:

  • Whether to have the different levels/scenes progressively unlock, or to make them all available from the beginning.
  • Implementing a “medals” system similar to the one used in Flappy Bird with bronze, silver, and gold levels depending on how many critters you herd into the pen. And then maybe you’d need at least a bronze medal to unlock the next level? I don’t know. Still thinking about it.

What’s Next

Now that I have a very simple menu structure set up, it should be relatively painless for me to set up things like iAd, sharing a score via the share sheet, and adding an option to turn off the sound effects. My goal from now until the baby is born in March is to make it so that the only thing I have left to do is add the art, music, and remaining sound effects.

It looks like I started the Xcode project on November 20th, which means I’ve been working on this for a little over two months now (and sometimes only for a couple hours a week). With that in mind, and knowing that it’ll take me a long time to do graphics and music, I’m hoping it’s reasonable to expect the game to be ready to ship sometime before my birthday in July!