对于swift 3.0

import Foundation

var str = " Hear me calling"

extension String {
    var stringByRemovingWhitespaces: String {
        return components(separatedBy: .whitespaces).joined()
    }
}

str.stringByRemovingWhitespaces  // Hearmecalling

extension String {

    var removingWhitespaceAndNewLines: String {
        return removing(.whitespacesAndNewlines)
    }

    func removing(_ forbiddenCharacters: CharacterSet) -> String {
        return String(unicodeScalars.filter({ !forbiddenCharacters.contains($0) }))
    }
}

我会使用这个扩展，以灵活和模仿其他集合如何做到这一点:

extension String {
    func filter(pred: Character -> Bool) -> String {
        var res = String()
        for c in self.characters {
            if pred(c) {
                res.append(c)
            }
        }
        return res
    }
}

"this is a String".filter { $0 != Character(" ") } // "thisisaString"

另一个答案是，有时输入字符串在单词之间可以包含多个空格。如果你需要标准化，单词之间只有一个空格，试试这个(Swift 4/5)

let inputString = "  a very     strange   text !    "
let validInput = inputString.components(separatedBy:.whitespacesAndNewlines).filter { $0.count > 0 }.joined(separator: " ")

print(validInput) // "a very strange text !"

羽毛球猫的答案的Swift 3版本

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

    func removeWhitespace() -> String {
        return self.replace(" ", replacement: "")
    }
}

这个String扩展删除了字符串中的所有空格，而不仅仅是尾随空格…

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

    func removeWhitespace() -> String {
        return self.replace(string: " ", replacement: "")
    }
  }

例子:

let string = "The quick brown dog jumps over the foxy lady."
let result = string.removeWhitespace() // Thequickbrowndogjumpsoverthefoxylady.