string - 无法使用类型为 'Range' 的参数列表调用类型为 '(start: String.Index, end: String.Index)' 的初始值设定项

Question

let greenHex = hex.substring(with: Range<String.Index>(start: hex.index(hex.startIndex, offsetBy: 2), end: hex.index(hex.startIndex, offsetBy: 4)))

这是Swift3.0，hex是一个字符串，但是这段代码会报错:

Cannot invoke initializer for type 'Range' with an argument list of type '(start: String.Index, end: String.Index)'

Answer 1

Range.init(start:end:)构造函数在 Swift 3.0 中被移除，所以你可以像下面这样初始化一个范围:

let range = hex.index(hex.startIndex, offsetBy: 2)..<hex.index(hex.startIndex, offsetBy: 4)

它返回类型为 <String.Index> 的半开范围.然后，您可以执行以下操作:

hex.substring(with: range)