Swift String常用方法

       参考Java String类， 对Swift String用法做个总结。

基础篇：

1、 字符串长度： 3种方法。

let str = "12345678"
let len1 = strlen(str) //8
let len2 = str.count  //8
let len3 = (str as NSString).length  //8

2、字符串拼接:  使用加好或者append函数。

let str1 = "abc" + "cde"
var str = "abc"
str.append("cde")

3、字符串遍历：

let str = "abcdefg"
for char in str {
    print(char)
}

let str = "abcdefg"
for index in str.indices.indices {
    print(str[index])   //通过下标访问
}

或带下标

let str = "abcdefg"
for (index, value) in str.enumerated() {
    print("\(index) --- \(value)")
}

4、字符串全部大写或小写：

let str = "abcdefg"
print(str.lowercased())  //全部小写
print(str.uppercased())  //全部大写

5、多行字符串使用3个双引号。

let verse = """
    To be, or not to be - that is the question;
    Whether 'tis nobler in the mind to suffer
    The slings and arrows of outrageous fortune,
    Or to take arms against a sea of troubles,
"""

6、ascii码

let ascii = UnicodeScalar("a")?.value   //a的ascii码
print(ascii ?? "") //97

7、截取子字符串

let str = "abcdefg"
let indexD = str.index(of: "d")
let sub = str[indexD!...] //defg
let sub1 = str[indexD!..

或

let sub3 = (str as NSString).substring(to: 3)  //abc
let sub4 = (str as NSString).substring(with: NSMakeRange(2, 3))  //cde

8、判断是否含有字符(串）

let str = "abcdefg"
print(str.contains("cd"))   //true
print(str.contains("c"))    //true
print(str.contains("o"))    //false

9、字符串分割

//字符串拆分(以单个或多个字符为分隔符)
let str = "abcdefg$$aaaa$$bbbb$$ccc"
let des1 = (str as NSString).components(separatedBy: "$$")
let des2 = str.components(separatedBy: "$$")
print(des1)  //["abcdefg", "aaaa", "bbbb", "ccc"]
print(des2) //["abcdefg", "aaaa", "bbbb", "ccc"]

10、字符串替换：

let str = "abcdefg$$aaaa$$bbbb$$ccc"
let dest11 = str.replacingOccurrences(of: "$$", with: "**")
print(dest11)

进阶篇：
1、获取下标字符：

extension String {
    //获取下标对应的字符
    func charAt(pos: Int) -> Character? {
        if pos < 0 || pos >= count {
            return nil   //判断边界条件
        }
        let index = self.index(self.startIndex, offsetBy: pos)
        let str = self[index]
        return Character(String(str))
    }
}
let str = "abcdef"
print(str.charAt(pos: 1)!)  //b

2、找出字符串中最长的子串， 字符串中包含中文、特殊字符、字母、数字等等。 思路： 使用正则找出所有字符串， 然后按长度排序找到最长的。

//找出字符串中英文字母最长的一个
func LongestWord(_ sen: String) -> String {
    let regx = try? NSRegularExpression(pattern: "[a-zA-Z]+", options: .caseInsensitive)
    
    if let results = regx?.matches(in: sen, options: [], range: NSMakeRange(0, sen.count)) {
        var array: [String] = []
        for item in results {
            let cur = (sen as NSString).substring(with: item.range)
            array.append(cur)  //找出所有符合要求的字符串
        }
        array.sort(by: { a,b in
            if a.count > b.count {     //降序排列
                return true
            } else {
                return false
            }
        })
        
        return array[0]  //最长的字符串
    }
    
    return sen
}

let ret = LongestWord("this is a test demo.1234324234穿插着中文和特殊字母@#@#adfsdfsdf!@#@$adfsdf")
print(ret)  //adfsdfsdf

3、字符串首字母变成大写(考虑字符串中有标点符号)：

//首字母大写, 要求支持标点
func LetterCapitalize(_ str: String) -> String {
    
    var result = ""

    for i in 0..= UnicodeScalar("a")!.value && UnicodeScalar(String(pre!))!.value <= UnicodeScalar("z")!.value)
                || (UnicodeScalar(String(pre!))!.value >= UnicodeScalar("A")!.value && UnicodeScalar(String(pre!))!.value <= UnicodeScalar("Z")!.value){
                result.append(String(cur!))
            } else {
                result.append(String(cur!).uppercased())
            }
            
        }
    }
    
    return result
    
}
let ret = LetterCapitalize("this a test message")
print(ret)

4、获取UILable控件显示String需要的高度

extension String {
    /**
     * 查询lable高度
     * @param fontSize, 字体大小
     * @param width, lable宽度
     */
    func getLableHeightByWidth(_ fontSize: CGFloat,
                               width: CGFloat,
                               font: UIFont) -> CGFloat {
        let size = CGSize(width: width, height: CGFloat.greatestFiniteMagnitude)
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.lineBreakMode = .byWordWrapping
        let attributes = [NSFontAttributeName:font,
                          NSParagraphStyleAttributeName:paragraphStyle.copy()]
        
        let text = self as NSString
        let rect = text.boundingRect(with: size, options:.usesLineFragmentOrigin, attributes: attributes, context:nil)
        return rect.size.height
    }
    
}