var str = "This is my string"
str = str.replacingOccurrences(of: " ", with: "+")
print(str)

Swift 3, Swift 4, Swift 5解决方案

let exampleString = "Example string"

//Solution suggested above in Swift 3.0
let stringToArray = exampleString.components(separatedBy: " ")
let stringFromArray = stringToArray.joined(separator: "+")

//Swiftiest solution
let swiftyString = exampleString.replacingOccurrences(of: " ", with: "+")

你可以用这个:

let s = "This is my string"
let modified = s.replace(" ", withString:"+")    

如果你在你的代码中添加这个扩展方法:

extension String
{
    func replace(target: String, withString: String) -> String
    {
       return self.stringByReplacingOccurrencesOfString(target, withString: withString, options: NSStringCompareOptions.LiteralSearch, range: nil)
    }
}

斯威夫特3:

extension String
{
    func replace(target: String, withString: String) -> String
    {
        return self.replacingOccurrences(of: target, with: withString, options: NSString.CompareOptions.literal, range: nil)
    }
}

很少发生在我身上，我只是想改变字符串中的(一个单词或字符)

所以我用了字典

  extension String{
    func replace(_ dictionary: [String: String]) -> String{
          var result = String()
          var i = -1
          for (of , with): (String, String)in dictionary{
              i += 1
              if i<1{
                  result = self.replacingOccurrences(of: of, with: with)
              }else{
                  result = result.replacingOccurrences(of: of, with: with)
              }
          }
        return result
     }
    }

使用

let mobile = "+1 (800) 444-9999"
let dictionary = ["+": "00", " ": "", "(": "", ")": "", "-": ""]
let mobileResult = mobile.replace(dictionary)
print(mobileResult) // 001800444999

下面是Swift 3的示例:

var stringToReplace = "This my string"
if let range = stringToReplace.range(of: "my") {
   stringToReplace?.replaceSubrange(range, with: "your")
} 

我认为Regex是最灵活和可靠的方法:

var str = "This is my string"
let regex = try! NSRegularExpression(pattern: " ", options: [])
let output = regex.stringByReplacingMatchesInString(
    str,
    options: [],
    range: NSRange(location: 0, length: str.characters.count),
    withTemplate: "+"
)
// output: "This+is+my+string"