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]

编程时，我经常用简单的A-Za-z和0-9组成的字符串。不需要困难的索引操作。这个扩展是基于普通的老左/中/右函数。

extension String {

    // LEFT
    // Returns the specified number of chars from the left of the string
    // let str = "Hello"
    // print(str.left(3))         // Hel
    func left(_ to: Int) -> String {
        return "\(self[..<self.index(startIndex, offsetBy: to)])"
    }

    // RIGHT
    // Returns the specified number of chars from the right of the string
    // let str = "Hello"
    // print(str.left(3))         // llo
    func right(_ from: Int) -> String {
        return "\(self[self.index(startIndex, offsetBy: self.length-from)...])"
    }

    // MID
    // Returns the specified number of chars from the startpoint of the string
    // let str = "Hello"
    // print(str.left(2,amount: 2))         // ll
    func mid(_ from: Int, amount: Int) -> String {
        let x = "\(self[self.index(startIndex, offsetBy: from)...])"
        return x.left(amount)
    }
}

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)
  }
}

var str = "Hello, playground"
let indexcut = str.firstIndex(of: ",")
print(String(str[..<indexcut!]))
print(String(str[indexcut!...]))

你可以试着用这种方法，并会得到适当的结果。

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。