How to fix "Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value" error in Swift?

Question

I'm currently taking an iOS game development course on Make School. The first step in this course is to. make a game which is similar to flappy bird, with some of the basics like procedural generation and infinite scrolling, so on so forth. I am not familiar with Swift, so I can't really explain the mechanics of the game yet, but I'll link the course page below:

Make School - iOS Game Development - Obstacles

In this section, the course focuses on procedurally generating obstacles from a source obstacle. Here's the code:

import SpriteKit
import GameplayKit

class GameScene: SKScene {

    var hero: SKSpriteNode!
    var scrollLayer: SKNode!
    var sinceTouch : CFTimeInterval = 0
    var spawnTimer: CFTimeInterval = 0
    let fixedDelta: CFTimeInterval = 1.0 / 60.0 /* 60 FPS */
    let scrollSpeed: CGFloat = 100
    var obstacleSource: SKNode!
    var obstacleLayer: SKNode!

    override func didMove(to view: SKView) {
        /* Setup your scene here */

        /* Recursive node search for 'hero' (child of referenced node) */
        hero = (self.childNode(withName: "//hero") as! SKSpriteNode)

        /* Set reference to scroll layer node */
        scrollLayer = self.childNode(withName: "scrollLayer")

        /* Set reference to obstacle layer node */
        obstacleLayer = self.childNode(withName: "obstacleLayer")

        /* allows the hero to animate when it's in the GameScene */
        hero.isPaused = false

        /* Set reference to obstacle Source node */
        obstacleSource = self.childNode(withName: "obstacle")
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        /* Called when a touch begins */

        /* Apply vertical impulse */
        hero.physicsBody?.applyImpulse(CGVector(dx: 0, dy: 300))

         /* Apply subtle rotation */
         hero.physicsBody?.applyAngularImpulse(1)

         /* Reset touch timer */
         sinceTouch = 0
    }

    override func update(_ currentTime: TimeInterval) {
        /* Called before each frame is rendered */

        /* Grab current velocity */
        let velocityY = hero.physicsBody?.velocity.dy ?? 0

        /* Check and cap vertical velocity */
        if velocityY > 400 {
          hero.physicsBody?.velocity.dy = 400
        }

        /* Apply falling rotation */
        if sinceTouch > 0.2 {
            let impulse = -20000 * fixedDelta
            hero.physicsBody?.applyAngularImpulse(CGFloat(impulse))
        }

        /* Clamp rotation */
        hero.zRotation.clamp(v1: CGFloat(-90).degreesToRadians(), CGFloat(30).degreesToRadians())
        hero.physicsBody?.angularVelocity.clamp(v1: -1, 3)

        /* Update last touch timer */
        sinceTouch += fixedDelta

        /* Process world scrolling */
        scrollWorld()

        /* Process obstacle scrolling*/
        updateObstacles()

        spawnTimer+=fixedDelta
    }

    func scrollWorld() {
        /* Scroll World */
        scrollLayer.position.x -= scrollSpeed * CGFloat(fixedDelta)

        /* Loop through scroll layer nodes */
        for ground in scrollLayer.children as! [SKSpriteNode] {

            /* Get ground node position, convert node position to scene space */
            let groundPosition = scrollLayer.convert(ground.position, to: self)

            /* Check if ground sprite has left the scene */
            if groundPosition.x <= -ground.size.width / 2 {

                    /* Reposition ground sprite to the second starting position */
                    let newPosition = CGPoint(x: (self.size.width / 2) + ground.size.width, y: groundPosition.y)

                    /* Convert new node position back to scroll layer space */
                    ground.position = self.convert(newPosition, to: scrollLayer)
            }
        }
    }

    func updateObstacles() {
      /* Update Obstacles */

      obstacleLayer.position.x -= scrollSpeed * CGFloat(fixedDelta)

      /* Loop through obstacle layer nodes */
      for obstacle in obstacleLayer.children as! [SKReferenceNode] {

          /* Get obstacle node position, convert node position to scene space */
          let obstaclePosition = obstacleLayer.convert(obstacle.position, to: self)

          /* Check if obstacle has left the scene */
          if obstaclePosition.x <= -26 {
          // 26 is one half the width of an obstacle

              /* Remove obstacle node from obstacle layer */
              obstacle.removeFromParent()
          }

      }

        /* Time to add a new obstacle? */
        if spawnTimer >= 1.5 {

            /* Create a new obstacle by copying the source obstacle */
            let newObstacle = obstacleSource.copy() as! SKNode
            obstacleLayer.addChild(newObstacle)

            /* Generate new obstacle position, start just outside screen and with a random y value */
            let randomPosition =  CGPoint(x: 347, y: CGFloat.random(in: 234...382))

            /* Convert new node position back to obstacle layer space */
            newObstacle.position = self.convert(randomPosition, to: obstacleLayer)

            // Reset spawn timer
            spawnTimer = 0
        }
    }
}

When I run this code in Xcode, the problem shows up in the line let newObstacle = obstacleSource.copy() as! SKNode

I checked the code a few times and even copy-pasted from the course-page, yet I still can't figure out the problem

Edit 1: Added screenshot of error, and hierarchy.

Edit 2: Added extra resources.

Here's a link to a screen recording

Here's a link to the whole file

Answer 1

Check for the nil

let newObstacle = obstacleSource.copy() as! SKNode

->

if let newObstacle = obstacleSource.copy() as? SKNode {
    //newObstacle is SKNode
}

Answer 2

This error (Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value) could be happening for a whole lot of reasons when you're trying to access/unwrap a value that is nil.

In your case, this is happening because obstacleSource variable is nil.

Which in turns makes your app crash when you try to access it via obstacleSource.copy() as? SKNode.

Since you initialize your obstacleSource variable like so:

obstacleSource = self.childNode(withName: "obstacle")

It means that the child node with the name "obstacle" can't be found in your scene, so you should simply check your GameScene.sks file and make sure your node is properly named ("obstacle").

And it would work as expected.

Now let's say that for any reasons you're not sure that your node obstacle actually exist, then in that case instead of declaring your node as an implicitly unwrapped optional:

var obstacleSource: SKNode!

You should initialize it as an optional like so:

var obstacleSource: SKNode?

In that case, because it's declared as an optional, your app won't crash and you can make sure your variable actually holds a value by using optional binding:

if let obstacleSource = self.obstacleSource {
   // Access your node here
} else {
   // The node 'obstacle' could not be found
}

Edit: Thanks for adding a screenshot in your question! The reason why the app crashes is because your node name doesn't match. You should simply rename the referencing node "obstacle" since that's how you're accessing it in your code, and it should work just fine!