swift中String基本使用

1、字符串截取，截取字符串从m到n位置的字符串

let index = self.titleString.startIndex

let staetIndex = self.titleString.index(index, offsetBy: m)

let endIndex = self.titleString.index(index, offsetBy: n)

self.titleLabel.text = String(self.titleString[staetIndex...endIndex])