如何在Swift中的字符串中的特定索引处添加字符

也许Swift 4的这个扩展会有所帮助：

extension String {
  mutating func insert(string:String,ind:Int) {
    self.insert(contentsOf: string, at:self.index(self.startIndex, offsetBy: ind) )
  }
}

var phone ="+ 9945555555"

var indx = phone.index(phone.startIndex,offsetBy:4)

phone.insert(" - ",at:indx)

index = phone.index(phone.startIndex,offsetBy:7)

phone.insert(" - ",at:indx)

// + 994-55-55555

如果你宣布它NSMutableString是可能的,你可以这样做:

let str: NSMutableString = "3022513240)"
str.insert("(", at: 0)
print(str)

输出是:

(3022513240)

编辑:

如果你想在开始时添加:

var str = "3022513240)"
str.insert("(", at: str.startIndex)

如果要在最后一个索引处添加字符:

str.insert("(", at: str.endIndex)

如果你想添加特定的索引:

str.insert("(", at: str.index(str.startIndex, offsetBy: 2))

斯威夫特3

使用本机Swift方法:

var welcome = "hello"

welcome.insert("!", at: welcome.endIndex) // prints hello!
welcome.insert("!", at: welcome.startIndex) // prints !hello
welcome.insert("!", at: welcome.index(before: welcome.endIndex)) // prints hell!o
welcome.insert("!", at: welcome.index(after: welcome.startIndex)) // prints h!ello
welcome.insert("!", at: welcome.index(welcome.startIndex, offsetBy: 3)) // prints hel!lo

如果您有兴趣了解有关字符串和性能的更多信息,请查看下面的@Thomas Deniau的答案.

var myString = "hell"
let index = 4
let character = "o" as Character

myString.insert(
    character, at:
    myString.index(myString.startIndex, offsetBy: index)
)

print(myString) // "hello"

小心:确保index大于或等于字符串的大小,否则你会崩溃.

将10位电话号码显示为美国号码格式（###）###-#### SWIFT 3

func arrangeUSFormat(strPhone : String)-> String {
    var strUpdated = strPhone
    if strPhone.characters.count == 10 {
        strUpdated.insert("(", at: strUpdated.startIndex)
        strUpdated.insert(")", at: strUpdated.index(strUpdated.startIndex, offsetBy: 4))
        strUpdated.insert(" ", at: strUpdated.index(strUpdated.startIndex, offsetBy: 5))
        strUpdated.insert("-", at: strUpdated.index(strUpdated.startIndex, offsetBy: 9))
    }
    return strUpdated
}