Swift 5和4.2

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

将字符串截断为特定长度

如果你已经输入了一段句子/文本，你想只保存指定长度的文本。将以下扩展添加到类中

extension String {

   func trunc(_ length: Int) -> String {
    if self.characters.count > length {
        return self.substring(to: self.characters.index(self.startIndex, offsetBy: length))
    } else {
        return self
    }
  }

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

}

Use

var str = "Lorem Ipsum is simply dummy text of the printing and typesetting industry."
//str is length 74
print(str)
//O/P:  Lorem Ipsum is simply dummy text of the printing and typesetting industry.

str = str.trunc(40)
print(str)
//O/P: Lorem Ipsum is simply dummy text of the 

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)

把这段代码放在你项目的一个文件中，比如Utils.swift:

extension String {   
    func trim() -> String {
        return self.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())
    }
}

所以你可以这样做:

let result = " abc ".trim()
// result == "abc"

Swift 3.0解决方案

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

所以你可以这样做:

let result = " Hello World ".trim()
// result = "HelloWorld"

下面介绍如何从字符串的开头和结尾删除所有空白。

(用Swift 2.0测试的示例。)

let myString = "  \t\t  Let's trim all the whitespace  \n \t  \n  "
let trimmedString = myString.stringByTrimmingCharactersInSet(
    NSCharacterSet.whitespaceAndNewlineCharacterSet()
)
// Returns "Let's trim all the whitespace"

(用Swift 3+测试的示例。)

let myString = "  \t\t  Let's trim all the whitespace  \n \t  \n  "
let trimmedString = myString.trimmingCharacters(in: .whitespacesAndNewlines)
// Returns "Let's trim all the whitespace"

**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"