Swift 4 (Xcode 9.1)

extension String {
    var capEachWord: String {
        return self.split(separator: " ").map { word in
            return String([word.startIndex]).uppercased() + word.lowercased().dropFirst()
        }.joined(separator: " ")
    }
}

下面是我一小步一小步完成的方法，类似于@Kirsteins。

func capitalizedPhrase(phrase:String) -> String {
    let firstCharIndex = advance(phrase.startIndex, 1)
    let firstChar = phrase.substringToIndex(firstCharIndex).uppercaseString
    let firstCharRange = phrase.startIndex..<firstCharIndex
    return phrase.stringByReplacingCharactersInRange(firstCharRange, withString: firstChar)
}

全部小写。小写()

首字母大写，其他字母小写，大写

全部大写。uppercase ()

字符串中的第一个字符大写

extension String {
    var capitalizeFirst: String {
        if self.characters.count == 0 {
            return self

        return String(self[self.startIndex]).capitalized + String(self.characters.dropFirst())
    }
}

Swift 3 (xcode 8.3.3)

大写字符串的所有首字符

let str = "your string"
let capStr = str.capitalized

//Your String

全部大写

let str = "your string"
let upStr = str.uppercased()

//YOUR STRING

字符串的第一个字符只能大写

 var str = "your string"
 let capStr = String(str.characters.prefix(1)).uppercased() + String(str.characters.dropFirst())

//Your string

我假设您想要将整个单词串的第一个单词大写。例如:“我的猫很胖，我的脂肪很松弛”应该返回“我的猫很胖，我的脂肪很松弛”。

Swift 5:

为此，您可以导入Foundation，然后使用大写的属性。例子:

import Foundation
var x = "my cat is fat, and my fat is flabby"
print(x.capitalized)  //prints "My Cat Is Fat, And My Fat Is Flabby"

如果你想成为一个纯粹主义者，不导入基础，那么你可以创建一个字符串扩展。

extension String {
    func capitalize() -> String {
        let arr = self.split(separator: " ").map{String($0)}
        var result = [String]()
        for element in arr {
            result.append(String(element.uppercased().first ?? " ") + element.suffix(element.count-1))
        }
        return result.joined(separator: " ")
    }
}

然后你可以这样使用:

var x = "my cat is fat, and my fat is flabby"
print(x.capitalize()) //prints "My Cat Is Fat, And My Fat Is Flabby"