Array empty when it should clearly contain elements - ios

Question

I keep getting a fatal error: Index out of range error. My array should clearly contain elements from the images below but it is empty. Been Trying to debug it for hours, I am not too sure what's causing. Please see the images and code below.
var topTest = [t2, t4, t8, t7, t2, t5, t8, t6 ]
for (index, point) in topTest.enumerate() {
spritesPath.append(point)
if index < topTest.count - 1 {
var previousArrayIndex = (index - 1)%topTest.count
if previousArrayIndex == -1 {
previousArrayIndex += topTest.count
}
var nextArrayIndex = (index + 1)%topTest.count
var firstIndex = topPositions.indexOf(point)
var secondIndex = topPositions.indexOf(topTest[nextArrayIndex])
var firstArray = top[firstIndex!]
var secondArray = top[secondIndex!]
var middleIndex1 = 0
var middleArray1 = [CGPoint]()
var middleRandomArrayLength1 : UInt32 = 0
var middleRandomPointIndex1 = 0
var middleIndex2 = 0
var middleArray2 = [CGPoint]()
var middleRandomArrayLength2 : UInt32 = 0
var middleRandomPointIndex2 = 0
if point.x > topTest[nextArrayIndex].x {
if point.x > topTest[previousArrayIndex].x {
let rightPositionsX = rightPositions.map({ $0.x })
middleArray1 = firstArray.filter({rightPositionsX.contains($0.x)})
middleRandomArrayLength1 = UInt32(middleArray1.count)
middleRandomPointIndex1 = Int(arc4random_uniform(middleRandomArrayLength1))
spritesPath.append(middleArray1[middleRandomPointIndex1])
middleIndex1 = rightPositions.indexOf(middleArray1[middleRandomPointIndex1])!
middleArray1 = right[middleIndex1]
let middleArray1X = middleArray1.map({ $0.x })
var midArray2 = secondArray.filter({middleArray1X.contains($0.x)})
midArray2 = midArray2.filter({element in point.x > element.x && topTest[nextArrayIndex].x < element.x })
middleRandomArrayLength2 = UInt32(midArray2.count)
middleRandomPointIndex2 = Int(arc4random_uniform(middleRandomArrayLength2))
spritesPath.append(middleArray2[middleRandomPointIndex2])
}
else{
let secondArrayX = secondArray.map({ $0.x })
middleArray1 = firstArray.filter({secondArrayX.contains($0.x)})
middleArray1 = middleArray1.filter({element in point.x > element.x && topTest[nextArrayIndex].x < element.x })
middleRandomArrayLength1 = UInt32(middleArray1.count)
middleRandomPointIndex1 = Int(arc4random_uniform(middleRandomArrayLength1))
spritesPath.append(middleArray1[middleRandomPointIndex1])
}
}
else
{
if point.x < topTest[previousArrayIndex].x {
let leftPositionsX = leftPositions.map({ $0.x })
middleArray1 = firstArray.filter({leftPositionsX.contains($0.x)})
middleRandomArrayLength1 = UInt32(middleArray1.count)
middleRandomPointIndex1 = Int(arc4random_uniform(middleRandomArrayLength1))
spritesPath.append(middleArray1[middleRandomPointIndex1])
middleIndex1 = leftPositions.indexOf(middleArray1[middleRandomPointIndex1])!
middleArray1 = left[middleIndex1]
let middleArray1X = middleArray1.map({ $0.x })
var midArray2 = secondArray.filter({middleArray1X.contains($0.x)})
midArray2 = midArray2.filter({element in point.x < element.x && topTest[nextArrayIndex].x > element.x })
middleRandomArrayLength2 = UInt32(midArray2.count)
middleRandomPointIndex2 = Int(arc4random_uniform(middleRandomArrayLength2))
spritesPath.append(midArray2[middleRandomPointIndex2])
}
else {
let secondArrayX = secondArray.map({ $0.x })
middleArray1 = firstArray.filter({secondArrayX.contains($0.x)})
middleArray1 = middleArray1.filter({element in point.x < element.x && topTest[nextArrayIndex].x > element.x })
middleRandomArrayLength1 = UInt32(middleArray1.count)
middleRandomPointIndex1 = Int(arc4random_uniform(middleRandomArrayLength1))
spritesPath.append(middleArray1[middleRandomPointIndex1])
}
}
}
}
The images below show that secondArray and middleArray contain similar elements and should not be empty

Answer 1

I think I can see an issue. The line that's crashing is:
spritesPath.append(middleArray2[middleRandomPointIndex2]) right?
So my theory is that if middleArray2 is empty then the index returned by arc4random_uniform is zero. But the array doesn't have a zeroeth element.
If so, check for this condition before getting the array element. Might be a good time to factor the random index code out into its own function, you're using it quite a bit and it would simplify your design.
Maybe:
func randomElement(fromArray array:[T]) -> T? {
let upperBound = UInt32(array.count)
guard upperBound > 0 else { return nil }
let index = Int(arc4random_uniform(upperBound))
return array[index]
}
let a = randomElement(fromArray: [1, 2, 3, 4, 5, 6, 7]) // 4
let b = randomElement(fromArray: ["red", "green", "blue"]) // "red"
let c = randomElement(fromArray: [Double]()) // nil
This function returns an optional because the array may not have any elements to return!