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
我使用的简单方法是:
String(Array(str)[2...4])
其他回答
一些有用的扩展:
extension String {
func substring(from: Int, to: Int) -> String {
let start = index(startIndex, offsetBy: from)
let end = index(start, offsetBy: to - from)
return String(self[start ..< end])
}
func substring(range: NSRange) -> String {
return substring(from: range.lowerBound, to: range.upperBound)
}
}
如果你只是想获取一个特定字符的子字符串，你不需要先找到索引，你可以只使用prefix(while:)方法
let str = "Hello, playground"
let subString = str.prefix { $0 != "," } // "Hello" as a String.SubSequence
希望对大家有所帮助。
extension String {
func getSubString(_ char: Character) -> String {
var subString = ""
for eachChar in self {
if eachChar == char {
return subString
} else {
subString += String(eachChar)
}
}
return subString
}
}
let str: String = "Hello, playground"
print(str.getSubString(","))
Swift 5,4
使用
let text = "Hello world"
text[0] // H
text[...3] // "Hell"
text[6..<text.count] // world
text[NSRange(location: 6, length: 3)] // wor
Code
import Foundation
public extension String {
subscript(value: Int) -> Character {
self[index(at: value)]
}
}
public extension String {
subscript(value: NSRange) -> Substring {
self[value.lowerBound..<value.upperBound]
}
}
public extension String {
subscript(value: CountableClosedRange<Int>) -> Substring {
self[index(at: value.lowerBound)...index(at: value.upperBound)]
}
subscript(value: CountableRange<Int>) -> Substring {
self[index(at: value.lowerBound)..<index(at: value.upperBound)]
}
subscript(value: PartialRangeUpTo<Int>) -> Substring {
self[..<index(at: value.upperBound)]
}
subscript(value: PartialRangeThrough<Int>) -> Substring {
self[...index(at: value.upperBound)]
}
subscript(value: PartialRangeFrom<Int>) -> Substring {
self[index(at: value.lowerBound)...]
}
}
private extension String {
func index(at offset: Int) -> String.Index {
index(startIndex, offsetBy: offset)
}
}
使用Swift 4从字符串创建子字符串(前缀和后缀):
let str : String = "ilike"
for i in 0...str.count {
let index = str.index(str.startIndex, offsetBy: i) // String.Index
let prefix = str[..<index] // String.SubSequence
let suffix = str[index...] // String.SubSequence
print("prefix \(prefix), suffix : \(suffix)")
}
输出
prefix , suffix : ilike
prefix i, suffix : like
prefix il, suffix : ike
prefix ili, suffix : ke
prefix ilik, suffix : e
prefix ilike, suffix :
如果你想在两个索引之间生成一个子字符串，使用:
let substring1 = string[startIndex...endIndex] // including endIndex
let subString2 = string[startIndex..<endIndex] // excluding endIndex
