我有以下简单的代码写在Swift 3:
let str = "Hello, playground"
let index = str.index(of: ",")!
let newStr = str.substring(to: index)
在Xcode 9 beta 5中，我得到了以下警告:
'substring(to:)'已弃用:请使用带有'partial range from'操作符的字符串切片下标。
这个部分范围的切片下标如何在Swift 4中使用?
当前回答
Swift 4/5更短:
let string = "123456"
let firstThree = String(string.prefix(3)) //"123"
let lastThree = String(string.suffix(3)) //"456"
其他回答
用这个方法你可以得到字符串的特定范围。你需要传递起始索引和你想要的字符总数。
extension String{
func substring(fromIndex : Int,count : Int) -> String{
let startIndex = self.index(self.startIndex, offsetBy: fromIndex)
let endIndex = self.index(self.startIndex, offsetBy: fromIndex + count)
let range = startIndex..<endIndex
return String(self[range])
}
}
Swift5
(Java的子字符串方法):
extension String {
func subString(from: Int, to: Int) -> String {
let startIndex = self.index(self.startIndex, offsetBy: from)
let endIndex = self.index(self.startIndex, offsetBy: to)
return String(self[startIndex..<endIndex])
}
}
用法:
var str = "Hello, Nick Michaels"
print(str.subString(from:7,to:20))
// print Nick Michaels
substring(from: index)转换为[index…]
检查样品
let text = "1234567890"
let index = text.index(text.startIndex, offsetBy: 3)
text.substring(from: index) // "4567890" [Swift 3]
String(text[index...]) // "4567890" [Swift 4]
你的代码转换到Swift 4也可以这样做:
let str = "Hello, playground"
let index = str.index(of: ",")!
let substr = str.prefix(upTo: index)
你可以使用下面的代码来创建一个新的字符串:
let newString = String(str.prefix(upTo: index))
我写了一个字符串扩展替换' string: subString:'
extension String {
func sliceByCharacter(from: Character, to: Character) -> String? {
let fromIndex = self.index(self.index(of: from)!, offsetBy: 1)
let toIndex = self.index(self.index(of: to)!, offsetBy: -1)
return String(self[fromIndex...toIndex])
}
func sliceByString(from:String, to:String) -> String? {
//From - startIndex
var range = self.range(of: from)
let subString = String(self[range!.upperBound...])
//To - endIndex
range = subString.range(of: to)
return String(subString[..<range!.lowerBound])
}
}
用法:“日期(1511508780012+0530)”sliceByString(from: "("， to: "+") 示例结果:"1511508780012"
PS:可选选项被强制展开。如有需要，请添加类型安全检查。
