Swift错误:无法将'ArraySlice‘类型的值转换为所需的参数类型

Question

我收到了这个错误，并且是Swift的新手。我想获取数组>= 5的最后5个点，并将这5个点作为数组参数传递给函数。我如何才能做到这一点并克服这个错误？

无法将'ArraySlice‘类型的值转换为所需的参数类型'CGPoint’

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

Answer 1

您需要使用Array(Slice<Type>)方法将ArraySlice转换为Array

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

Answer 2

您可以使用返回ArraySlice的前缀(upTo end: Self.Index)方法代替范围操作符，这会使代码更短。方法的定义:该方法返回从集合开始到(但不包括)指定位置(索引)的子序列。

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

我尝试使用Array(lastFivePoints)，但遇到错误

表达式的

类型在没有更多上下文的情况下不明确

​

​

我最终做了：

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

其中T是本例中的内容类CGPoint