xcode: Thread 1: Signal SIGABART in class AppDelegate: UIResponder, UIApplicationDelegate (game application) - ios

Question

Before marking as duplicate, please consider that I have searched the web and StackOverflow but I didn't find any solution for this specific problem (because all questions about this error are for apps, not games).
I am making a very basic Space Shooter game and I reached a stage where I want to make the hero (code below) shoot bullets; I created a function spawn_bullet to do this. After I wrote this function and called it in the function:
override func update(currentTime: CFTimeInterval),
I get the error: Thread 1: signal SIGABRT. Image is shown below
I believe that the error has something to do with the execution of the spawn_bullet function but I am not sure where it is, why it caused and how to fix it. Anyone has an idea to fix it and if possible to provide enough details for why it causes?
Thank you!
NOTE
English is not my first language (that's why it's bad)
Below I provide my code used in GameScene.swift:
import SpriteKit
class GameScene: SKScene {
var hero = SKSpriteNode(imageNamed: "hero")
var bullet = SKSpriteNode(imageNamed: "bullet")
var enemy = SKSpriteNode(imageNamed: "enemy")
var init_bullet_position = CGFloat(0)
var bullet_velocityY = CGFloat(5)
override func didMoveToView(view: SKView) {
/* Setup your scene here */
self.backgroundColor = UIColor(red: 0.7, green: 0.7, blue: 0.8, alpha: 1)
self.hero.anchorPoint = CGPointMake(0.5, 0)
self.hero.size.height = 50
self.hero.size.width = 30
self.hero.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMinX(self.frame) + self.hero.size.height)
self.bullet.anchorPoint = CGPointMake(0.5, 0)
self.bullet.size.height = 30
self.bullet.size.width = 15
self.bullet.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMinX(self.frame) + self.hero.size.height + self.hero.size.height / 4)
self.init_bullet_position = CGFloat(CGRectGetMinX(self.frame) + self.hero.size.height + self.hero.size.height / 4)
self.hero.zPosition = 1; //1 = front
self.addChild(bullet)
self.addChild(hero)
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
/* Called when a touch begins */
for touch: AnyObject in touches {
let location = touch.locationInNode!(self)
hero.position.x = location.x
if self.bullet.position.y == init_bullet_position{
self.bullet.position.x = location.x
}
}
}
override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
/* Called when a touch begins */
for touch: AnyObject in touches {
let location = touch.locationInNode!(self)
self.hero.position.x = location.x
if self.bullet.position.y == init_bullet_position{
self.bullet.position.x = location.x
}
}
}
func spawn_bullets(){
self.bullet.anchorPoint = CGPointMake(0.5, 0)
self.bullet.size.height = 30
self.bullet.size.width = 15
self.bullet.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMinX(self.frame) + self.hero.size.height + self.hero.size.height / 4)
self.addChild(bullet)
if self.bullet.position.y < self.frame.size.height{
self.bullet.position.y += self.bullet_velocityY
}
}
override func update(currentTime: CFTimeInterval) {
/* Called before each frame is rendered */
spawn_bullets()
}
}
Here is the exception message:
2016-07-14 23:07:54.564 Space shooter[14391:191912] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attemped to add a SKNode which already has a parent: <SKSpriteNode> name:'(null)' texture:[<SKTexture> 'bullet' (400 x 600)] position:{160, 62.5} scale:{1.00, 1.00} size:{15, 30} anchor:{0.5, 0} rotation:0.00'
*** First throw call stack:
(
0 CoreFoundation 0x000000010ec4fd85 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x0000000111299deb objc_exception_throw + 48
2 CoreFoundation 0x000000010ec4fcbd +[NSException raise:format:] + 205
3 SpriteKit 0x000000010fb74903 -[SKNode insertChild:atIndex:] + 162
4 SpriteKit 0x000000010fb74840 -[SKNode addChild:] + 68
5 Space shooter 0x000000010ea62d23 _TFC13Space_shooter9GameScene13spawn_bulletsfT_T_ + 995
6 Space shooter 0x000000010ea62ef4 _TFC13Space_shooter9GameScene6updatefSdT_ + 36
7 Space shooter 0x000000010ea62f2c _TToFC13Space_shooter9GameScene6updatefSdT_ + 44
8 SpriteKit 0x000000010fb48072 -[SKScene _update:] + 312
9 SpriteKit 0x000000010fb6503a -[SKView _update:] + 932
10 SpriteKit 0x000000010fb6221a __59-[SKView _renderSynchronouslyForTime:preRender:postRender:]_block_invoke + 170
11 SpriteKit 0x000000010fb620e8 -[SKView _renderSynchronouslyForTime:preRender:postRender:] + 235
12 SpriteKit 0x000000010fb64ac2 -[SKView layoutSubviews] + 85
13 UIKit 0x000000010fdd8980 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 703
14 QuartzCore 0x00000001151d7c00 -[CALayer layoutSublayers] + 146
15 QuartzCore 0x00000001151cc08e _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 366
16 QuartzCore 0x00000001151cbf0c _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
17 QuartzCore 0x00000001151c03c9 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 277
18 QuartzCore 0x00000001151ee086 _ZN2CA11Transaction6commitEv + 486
19 QuartzCore 0x00000001151ee7f8 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 92
20 CoreFoundation 0x000000010eb74c37 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
21 CoreFoundation 0x000000010eb74ba7 __CFRunLoopDoObservers + 391
22 CoreFoundation 0x000000010eb6a11c CFRunLoopRunSpecific + 524
23 UIKit 0x000000010fd18f21 -[UIApplication _run] + 402
24 UIKit 0x000000010fd1df09 UIApplicationMain + 171
25 Space shooter 0x000000010ea64e82 main + 114
26 libdyld.dylib 0x0000000111dc792d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

It occurs on this line:
self.addChild(bullet)
This is because bullet already has a parent.
To fix it, add this line before you add the child:
bullet.removeFromParent()

Answer 2

To answer the stated question:
Here's your error:
Attemped to add a SKNode which already has a parent
The problem is in your spawn_bullets() function. You're not actually instantiating new bullets in this function. You're just updating properties on self's instance of bullet, then trying to add it as a child of your scene. The second time this function is called, it crashes, because the bullet is already a child of the scene.
Instead, you should create new instances of your bullet node.
Regarding the underlying problem of creating unique bullets:
This is a whole separate topic in and of itself. I assume you only want to fire bullets at specific times, such as when you tap on something, so rather than spawning bullets from the update() function, which is called before each frame is rendered, I would call spawn_bullets() from a tap method, or other interaction. Secondly, you will want to create new instances of your bullet instead of updating a variable on your scene. These can be added, animated, and subsequently removed. Finally, take a look at the SKAction class for actually animating (and ultimately removing) the bullets. For example:
let newBullet = SKSpriteNode(imageNamed: "bullet")
newBullet.position = CGPoint(x: 10, y: 10)
self.addChild(newBullet)
let moveAction = SKAction.moveTo(CGPoint(x: 50, y: 10), duration: 0.4)
let removeAction = SKAction.removeFromParent()
newBullet.runAction(SKAction.sequence([moveAction, removeAction])) {
// Bullet is done and removed.
}
You can do a lot more with SKAction than is shown here. You can play audio files, follow paths, or even simply run a block.