我不断收到 fatal error: Index out of range 错误。我的数组应该清楚地包含下图中的元素，但它是空的。几个小时以来一直在尝试调试它，我不太确定是什么原因造成的。请参阅下面的图片和代码。
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])
}
}
}
}
下图显示 secondArray 和 middleArray 包含类似的元素，不应为空
最佳答案
我想我可以看到一个问题。崩溃的行是:
spritesPath.append(middleArray2[middleRandomPointIndex2]) 对吧？
所以我的理论是，如果 middleArray2 为空，则 arc4random_uniform 返回的索引为零。但是该数组没有第 0 个元素。
如果是这样，请在获取数组元素之前检查此条件。可能是将随机索引代码分解到它自己的函数中的好时机，您经常使用它并且它会简化您的设计。
也许:
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
这个函数返回一个可选的，因为数组可能没有任何要返回的元素!
关于ios - 数组在本应明确包含元素时为空，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39053471/