iOS Swift中String的常用操作以及数据转化

一、String的常用操作

1、字符和字符串的定义

//常量字符串
let a = "james"
//变量字符串
var b = "wade"
b = "Paul"
//声明为nil的字符串
var c:String?
//空字符串(不提倡)
let d = String()
//空字符串，提倡用这样的字面量语法声明，类型可不指定，swift自动识别
var e = ""

2、判断字符串

//1、判断字符串是否为空
let e = "james"
let bl2:Bool = e.isEmpty
NSLog("The shoppingList firstItem %@", bl2 ? "YES" : "NO")

let e = "我是James的粉丝，还喜欢韦德"
//2、判断在字符串中包含某个字符（只能是一个）
if let index3 = e.characters.index(of: "韦"){
    //包含“韦”字符
    print("The value for index3 was \(index3).")
}
//3、判断在字符串中包含某个子字符串
if let range4 = e.range(of: "James"){
    //包含某个子字符串"James"
    print("The value for range4 was \(range4).")
}
//4、是否含有前缀
let bool1:Bool = e.hasPrefix("我是")  
//5、是否含有后缀
let bool2:Bool = e.hasSuffix("喜欢") 
print("The Prefix value for e was \(bool1).The Suffix value for e was \(bool2).")

3、 拼接和添加字符串

let str1 = "James，"
let str2 = "你好"
let str3 = "！"
//方法1:
var p_str1 = str1 + str2
//方法2:
var p_str2 = String(format:"%@ %@",str1,str2)
let p_str3 = String(format:"%@ %@ %@",str1,str2,str3)
//方法3:
let p_str4 = "霸气的 \(str1)\(str2)\(str3)"
print("The p_str1 value is \(p_str1);The p_str2 value is \(p_str2);The p_str3 value is\(p_str3);The p_str4 value is \(p_str4);")

//在后面添加字符／字符串
p_str1.append(str3)
//+=：用于在后面添加同类型的
p_str2 += str3
print("The new p_str1 value is \(p_str1);The new p_str2 value is \(p_str2);")

4、字符计数及字符串索引

//1、计算字符的个数
let wade = "holle wade"
let longth = wade.characters.count
print("The length of the str was \(longth).")
//2、字符串索引
//        wade.startIndex    //返回0
//        wade.endIndex      //最后一个字符串的下一个位置
print("wade startIndex was \(wade.startIndex).wade endIndex was \(wade.endIndex).")

//3、用字符串的字符数组的index(after:Index)或index(before:Index)引用Index后一个或前一个索引,来获取对应的元素
let after = wade[wade.characters.index(after: wade.startIndex)]  //b
let before = wade[wade.characters.index(before: wade.endIndex)]   //f
print("after was \(after).before was \(before).")

//4、索引3的元素
let index = wade.index(wade.startIndex,offsetBy:3)    //起始位置，偏移位
print("index was \(index).")
//5、确定index1的值是安全的，是否越界
let index1 = wade.index(wade.startIndex,offsetBy:3, limitedBy:wade.endIndex) //起始位置，偏移位，最后一个字符串的下一个位置
print("index was \(String(describing: index1)).")

5、插入字符或字符串

var StrinsertStr = "James很伟大"
//1、在开头插入一个字符，注意是字符不是字符串
StrinsertStr.insert("@", at: StrinsertStr.startIndex)
//2、在指定位置插入一个字符
StrinsertStr.insert("@", at: StrinsertStr.index(StrinsertStr.startIndex, offsetBy: 6))
print("insertStr was \(StrinsertStr)).")

//3、在开头字符的后面插入一个字符串
StrinsertStr.insert(contentsOf:"伟大的".characters, at: StrinsertStr.index(after: StrinsertStr.startIndex))    
//4、在结尾字符的前面插入一个字符串
StrinsertStr.insert(contentsOf:"，OK？".characters, at: StrinsertStr.index(before: StrinsertStr.endIndex)) 
//5、在指定位置插入一个字符串
var p_str5 = "interesting"
StrinsertStr.insert(contentsOf:p_str5.characters, at: StrinsertStr.endIndex)    
StrinsertStr.insert(contentsOf: ["~","~","~"], at: StrinsertStr.index(StrinsertStr.startIndex, offsetBy: 12))  
print("insertStr was \(StrinsertStr)).")

6、截取字符串

var ceptionStr = "勒布朗·詹姆斯一共获得了4个常规赛MVP"
//通过索引截取字符串
//从开头截取指定的长度
let preStr = String(ceptionStr.characters.prefix(3))
//从末尾截取指定的最大长度。
let sufStr = String(ceptionStr.characters.suffix(3))
//如果最大长度超过集合中元素的数目，则结果包含集合中的所有元素
let allStr = String(ceptionStr.characters.prefix(50))
print("preStr was \(preStr)。sufStr was \(sufStr)。allStr was \(allStr)")
//offsetBy:最大为endIndex  
let i = ceptionStr.index(ceptionStr.startIndex, offsetBy: 4)
let j = ceptionStr.index(ceptionStr.startIndex, offsetBy: 7)

//substring(to:)：从开头截取到指定的索引，不包含索引所在元素。
var ceptionStr1 = ceptionStr.substring(to: i)
print("ceptionStr1 was \(ceptionStr1)。")
//从指定的索引开始截取到末尾，包含索引所在元素。
ceptionStr1 = ceptionStr.substring(from: i)
print("ceptionStr2 was \(ceptionStr1)。")
//substring(with:)：包含指定的索引区间
ceptionStr1 = ceptionStr.substring(with: i..

7、替换字符串

let ceptionIndex = ceptionStr.characters.index(of: "4")
let offsetIndex = ceptionStr.index(ceptionIndex!, offsetBy: 1)
ceptionStr.replaceSubrange(ceptionIndex! ..< offsetIndex, with: "3")
//方法1:
let ceptionIndex2 = ceptionStr.characters.index(of: "常")
let offsetIndex2 = ceptionStr.index(ceptionIndex2!, offsetBy: 1)
ceptionStr.replaceSubrange(ceptionIndex2! ..< offsetIndex2, with: "季后")

// //方法1:（简易写法）
let range3 = ceptionStr.range(of: "常")
ceptionStr.replaceSubrange(range3!, with: "季后")
print("ceptionStr was \(ceptionStr)。")

8、删除字符串

var deleteStr = "勒布朗·詹姆斯（LeBron James）美国职业篮球运动员，司职小前锋，绰号“小皇帝”，效力于NBA克利夫兰骑士队。"
let x = deleteStr.index(deleteStr.startIndex, offsetBy: 8)
//1、在指定位置删除一个字符
deleteStr.remove(at: x)
print("deleteStr1 was \(deleteStr)。")
deleteStr.remove(at: deleteStr.startIndex)
print("deleteStr2 was \(deleteStr)。")
deleteStr.remove(at: deleteStr.index(after: deleteStr.startIndex))
print("deleteStr3 was \(deleteStr)。")
deleteStr.remove(at: deleteStr.index(before: deleteStr.endIndex))
print("deleteStr4 was \(deleteStr)。")

var originalStr = "勒布朗·詹姆斯（LeBron James）是美国职业篮球运动员，司职小前锋，绰号“小皇帝”，效力于NBA克利夫兰骑士队。"
//2、删除指定范围的字符
let ran1 = originalStr.range(of: "（LeBron James）")
originalStr.removeSubrange(ran1!)
print("originalStr2 was \(originalStr)。")

9、遍历字符串

let str = "variable"
//方法1
for word in str.characters {
    print(word)
}
//方法2
str.characters.forEach{print($0)}
//方法3
for (index3,value) in str.characters.enumerated() {
    print("\(index3) \(value)")
}

10、字符串的比较

let compareStr1 = "bei jing"
let compareStr2 = "BEI JING"

// 判读两个字符串是否相等
let bl3:Bool = str1 == str2
print("bl3的值\(bl3)")
// 比较两个字符串
let result1 = compareStr1.compare(compareStr2)
print(result1)
// 忽略大小写比较
let result2 = compareStr1.caseInsensitiveCompare(compareStr2)
print(result2)

二、字符串的转换

1、大小写字母转换

//1、转换为大写
var capitalStr = "LeBron James"
capitalStr = capitalStr.uppercased()
print("capitalStr was \(capitalStr)。")
//2、转换为小写
capitalStr = capitalStr.lowercased()
print("capitalStr2 was \(capitalStr)。")

2、字符串与数组的转换

var strArray = ["hello", "LeBron James", "2017"]
//数组通过指定字符拼接
let array_str1 = strArray.joined(separator: "-")
print("array_str1 was \(array_str1)。")
//拆分为数组
strArray = array_str1.components(separatedBy: "-")
print("strArray was \(strArray)。")

3、NSString和String类型转换

let Str1 = "LeBron James"
//定义NSString，String->NSString
let Str2 = NSString(string: Str1)
print("Str1 was \(Str1)。Str2 was \(Str2)，Str2的类型\(type(of:Str2)),Str1的类型\(type(of:Str1))")

//定义NSString，NSString -> String
let Str3:NSString = Str1 as NSString
let Str4 = Str3 as String    //类型推导，:String可省略

print("Str3的类型\(type(of:Str3)),Str4的类型\(type(of:Str4))")

4、字符串转数值

let string = "30"
print(string)
let nStr = string as NSString // 借用NSString输出
print(nStr)

print("doubleValue:\(nStr.doubleValue)")
print("floatValue:\(nStr.floatValue)")
print("intValue:\(nStr.intValue)")
print("integerValue:\(nStr.integerValue)")
print("longLongValue:\(nStr.longLongValue)")
print("boolValue:\(nStr.boolValue)")

三、NSString和SwiftString的区别

1、String类型是值类型，NSString是引用类型
* NSString初始化了一个指针指向了这个字符串，但Swift的String是把字符串字面量赋值给变量。
*即：声明创建后的对象NSString获得的是指向NSString类型的地址，而string获得的是一个值。
2、Swift的String字符串之间的拼接比NSString方便
NSString需要用append或者stringWithFormat将两个字符串拼接；而Swift的String只需要用 “+” 即可
3、Swift的String 可以实现字符串遍历
4、Swift的String独有的字符串插入字符功能

NSString和SwiftString的区别可以参看这篇文章