不要忘记导入Foundation或UIKit。

import Foundation
let trimmedString = "   aaa  "".trimmingCharacters(in: .whitespaces)
print(trimmedString)

结果:

"aaa"

否则你会得到:

error: value of type 'String' has no member 'trimmingCharacters'
    return self.trimmingCharacters(in: .whitespaces)

**Swift 5**

extension String {

    func trimAllSpace() -> String {
         return components(separatedBy: .whitespacesAndNewlines).joined()
    }
    
    func trimSpace() -> String {
        return self.trimmingCharacters(in: .whitespacesAndNewlines)
    }
}

**Use:**
let result = " abc ".trimAllSpace()
// result == "abc"
let ex = " abc cd  ".trimSpace()
// ex == "abc cd"

//Swift 4.0删除空格和新行

extension String {
    func trim() -> String {
        return self.trimmingCharacters(in: .whitespacesAndNewlines)         
    }
}

Swift 5和4.2

let trimmedString = " abc ".trimmingCharacters(in: .whitespaces)
 //trimmedString == "abc"

另一种类似的方式:

extension String {
    var trimmed:String {
        return self.trimmingCharacters(in: CharacterSet.whitespaces)
    }
}

使用:

let trimmedString = "myString ".trimmed

是的，你可以这样做:

var str = "  this is the answer   "
str = str.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
print(srt) // "this is the answer"

CharacterSet实际上是一个非常强大的工具，用于创建修剪规则，比. whitespacesandnewlines等预定义集更灵活。

例如:

var str = " Hello World !"
let cs = CharacterSet.init(charactersIn: " !")
str = str.trimmingCharacters(in: cs)
print(str) // "Hello World"