Swift for loop not working - ios

Question

I'm baffled by this loop in my Swift code that won't work. Here's the entirety of the function--"pulseChar" is giving me the error "index out of range":
func openingSequence(){
let nodeList = [self.drum,self.piano,self.guitarBoard]
let offset = SKAction.waitForDuration(10)
let stOne = SKAction.runBlock { () -> Void in
for var i in 0...nodeList.count-1{
nodeList[i].runAction(SKAction.fadeAlphaTo(0.3, duration: 0.3))
i++
}
}
let firstLineWait = SKAction.waitForDuration(4)
let moveSprites = SKAction.runBlock { () -> Void in
moveScale(self.rheaBoard, duration: 0.5, to: CGPoint(x: 100, y: self.frame.height - 85), size: 0.4)
moveScale(self.guitarBoard, duration: 0.5, to: CGPoint(x: self.frame.midX - self.frame.midX/2, y: 65), size: 0.35)
for var i in 0...nodeList.count-1{
nodeList[i].runAction(fadeI)
i++
}
}
let fadeAudio = SKAction.runBlock { () -> Void in
fadeOtherTracksOut([9,8,4,2,1])
}
let moveFade = SKAction.group([moveSprites,fadeAudio])
let pulseChar = SKAction.runBlock { () -> Void in
for var i in 0...nodeList.count-1{
self.background.runAction(SKAction.runBlock({ () -> Void in
pulse(nodeList[i], startScale: 0.35, endScale: 0.4)
}))
i++
}
self.startInteaction = true
}
background.runAction(SKAction.sequence([offset,stOne,firstLineWait,moveFade,pulseChar]))
}
My compiler is telling me that i = 3 when it fails...but "i" should not get to three, as
nodeList.count = 3
and I use the range
for var i in 0...nodeList.count-1
Also, the identical loops before it work just fine...what's going on here? I'm new to programming so if this is a ridiculously simple fix you'll have to excuse me. But help would be greatly appreciated.
EDIT
It seems that the operator i++ needed to be inside the runBlock:
let pulseChar = SKAction.runBlock { () -> Void in
for var i in 0...nodeList.count-1{
self.background.runAction(SKAction.runBlock({ () -> Void in
pulse(nodeList[i], startScale: 0.35, endScale: 0.4)
i++
}))
}
This fixes the problem, but I would really appreciate it if someone wouldn't mind explaining why this is the case. It seems to me that if the operator i++ is within the loop it should never == 3.

Answer 1

Don't increment the index variable i "manually", the repeat loop does that automatically.
And you can use the half-open range operator to avoid the extra subtraction, for example
for i in 0..<nodeList.count {
nodeList[i].runAction(SKAction.fadeAlphaTo(0.3, duration: 0.3))
}
or
for node in nodeList {
node.runAction(SKAction.fadeAlphaTo(0.3, duration: 0.3))
}
if the numeric index is not needed.
Or even
nodeList.forEach{ $0.runAction(SKAction.fadeAlphaTo(0.3, duration: 0.3)) }

Answer 2

From swift programming guide provided by apple Check Here For More Details
Care Fully look at the following code and it's output.
for index in 1...5 {
print("\(index) times 5 is \(index * 5)")
}
// 1 times 5 is 5
// 2 times 5 is 10
// 3 times 5 is 15
// 4 times 5 is 20
// 5 times 5 is 25
In For in loop we do not require to increment the counter.
The increment part is handled by the loop it self
Try Following Updated code.
func openingSequence(){
let nodeList = [self.drum,self.piano,self.guitarBoard]
let offset = SKAction.waitForDuration(10)
let stOne = SKAction.runBlock { () -> Void in
for var i in 0..<nodeList.count{
nodeList[i].runAction(SKAction.fadeAlphaTo(0.3, duration: 0.3))
}
}
let firstLineWait = SKAction.waitForDuration(4)
let moveSprites = SKAction.runBlock { () -> Void in
moveScale(self.rheaBoard, duration: 0.5, to: CGPoint(x: 100, y: self.frame.height - 85), size: 0.4)
moveScale(self.guitarBoard, duration: 0.5, to: CGPoint(x: self.frame.midX - self.frame.midX/2, y: 65), size: 0.35)
for var i in 0..<nodeList.count{
nodeList[i].runAction(fadeI)
}
}
let fadeAudio = SKAction.runBlock { () -> Void in
fadeOtherTracksOut([9,8,4,2,1])
}
let moveFade = SKAction.group([moveSprites,fadeAudio])
let pulseChar = SKAction.runBlock { () -> Void in
for var i in 0..<nodeList.count{
self.background.runAction(SKAction.runBlock({ () -> Void in
pulse(nodeList[i], startScale: 0.35, endScale: 0.4)
}))
}
self.startInteaction = true
}
background.runAction(SKAction.sequence([offset,stOne,firstLineWait,moveFade,pulseChar]))
}