Swift错误:无法将“ArraySlice”类型的值转换为预期的参数类型

Question

我收到此错误，并且是 Swift 的新手。我想取数组的最后 5 个点

无法将“ArraySlice”类型的值转换为预期的参数类型“[CGPoint]”

if (self.points?.count >= 5) {
    let lastFivePoints = self.points![(self.points!.count-5)..<self.points!.count]
    let angle = VectorCalculator.angleWithArrayOfPoints(lastFivePoints)
}

Answer 1

我尝试使用数组（最后五点），但我得到错误

表达式的类型在没有更多上下文的情况下是模棱两可的

我最终做了：

let arr = lastFivePoints.map({ (x) -> T in
                            return x
                        })

其中T是这个例子的内容类CGPoint

Answer 2

您可以使用前缀(upTo end: Self)来代替范围运算符。Index)方法，该方法返回数组切片，从而使代码更短。方法的定义:该方法返回一个子序列，从集合的开始处一直到(但不包括)指定的位置(索引)。

if (self.points?.count >= 5) {
  let lastFivePoints = Array<CGPoint>(self.points?.prefix(upTo:5)) as [AnyObject]
  let angle = VectorCalculator.angleWithArrayOfPoints(lastFivePoints)
}

// You can also do this 

let lastFivePoints = Array<CGPoint>(self.points?[0...4]) 

Answer 3

您需要使用方法< code>Array(Slice)将< code>ArraySlice转换为< code>Array

if (self.points?.count >= 5) {
    let lastFivePoints = Array(self.points![(self.points!.count-5)..<self.points!.count])
    let angle = VectorCalculator.angleWithArrayOfPoints(lastFivePoints)
}