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(","))

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]

转换子字符串(Swift 3)到字符串切片(Swift 4)

在Swift 3,4中:

let newStr = str.substring(to: index) // Swift 3
let newStr = String(str[..<index]) // Swift 4

let newStr = str.substring(from: index) // Swift 3
let newStr = String(str[index...]) // Swift 4 

let range = firstIndex..<secondIndex // If you have a range
let newStr = = str.substring(with: range) // Swift 3
let newStr = String(str[range])  // Swift 4

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(","))

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))

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。