Create an array of SKShapeNodes - ios

Question

I'm new to Swift development and I'm trying to create a simple racing game. The road in the game has lane markers that animate from the top of the screen to the bottom then loop back up to the top. I am using SKShapeNodes for the lane line markers.
I have been able to get one lane marker to work and now I just need to create an array(I think?) of lane markers so that I can have 2 columns of lanes and enough to give the game the illusion of being a real road.
I'm able to create the array but I get a run-time error when I try to add a SKShapeNode to it. The error I get is:
Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP,subcode=0x0)
fatal error: Cannot index empty buffer
Here is the relevant source code:
class PlayScene: SKScene {
let road = SKSpriteNode(imageNamed: "road8")
let car = SKSpriteNode(imageNamed: "car")
let laneLineNode = SKShapeNode()
var laneLineNodeArray = [[SKShapeNode]]()
var groundSpeed = 25
}
override func didMoveToView(view: SKView) {
//draw a lane line
var path = CGPathCreateMutable();
var laneLineWidth = self.size.width / 85
var laneLineHeight = self.size.height / 11
var laneLine = CGRect(x: ((self.frame.size.width / 5) * 2), y:
(self.frame.size.height + laneLineHeight),
width: laneLineWidth, height: laneLineHeight)
laneLineNode.lineWidth = 0
laneLineNode.path = CGPathCreateWithRect(laneLine, nil)
laneLineNode.fillColor = SKColor.yellowColor()
laneLineNode.zPosition = 2
//THIS IS THE LINE I GET THE ERROR ON
laneLineNodeArray[0][0] = laneLineNode
self.addChild(self.road)
self.addChild(self.laneLineNode)
self.addChild(self.car)
}
override func update(currentTime: CFTimeInterval) {
//move the lane lines
scrollLaneLines(self.scene!)
}
}
Thanks for any help you can give me.

Answer 1

First of all... You are closing your class too soon with this code:
var groundSpeed = 25
} // <--
Second... Your are not initializing your array before using it. In my test, I got the error because of that.
You should use this syntax to initialize your Array or use append as #Arnab suggest.
let laneLineNode = SKShapeNode()
var laneLineNodeArray = [[laneLineNode]]

Answer 2

You have created an empty array so far. Use "append" to add data to the array before you access the elements by index.

Answer 3

Thank you! I was able to get it to work with this in Class PlayScene:
var laneLineNodeArray:[[SKShapeNode]] = []
and this in func didMoveToView:
//draw a lane line
var path = CGPathCreateMutable();
var laneLineWidth = self.size.width / 85
var laneLineHeight = self.size.height / 11
var laneLine = CGRect(x: 0, y: (self.frame.size.height + laneLineHeight),
width: laneLineWidth, height: laneLineHeight)
var laneLineRowNumber: Int
var laneLineY: CGFloat
for r in 0...6 {
var laneLineRow:[LaneLine] = []
laneLineRowNumber = r
for c in 0...1 {
let laneLineNode = LaneLine()
laneLineNode.lineWidth = 0
laneLineNode.path = CGPathCreateWithRect(laneLine, nil)
laneLineNode.fillColor = SKColor.yellowColor()
laneLineNode.zPosition = 2
//lanelineY determines the Y placement of the lane.
laneLineY = self.frame.size.height - (CGFloat((laneLineHeight) * 2)
* CGFloat(r))
if c == 0 {
laneLineNode.position = CGPointMake(laneWidth * 2, laneLineY)
}
else if c == 1 {
laneLineNode.position = CGPointMake(laneWidth * 3, laneLineY)
}
self.addChild(laneLineNode)
laneLineRow.append(laneLineNode)
}
laneLineNodeArray.append(laneLineRow)
}