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String类中的API变化

1.大小写转换由原来的属性更改为方法

var string = "Hello, Swift"
//全部转换为大写
//swift2.2
//string = string.uppercaseString
//swift3.0
string = string.uppercased()
//全部转换为小写
//swift2.2
//string = string.lowercaseString
//swift3.0
string = string.lowercased()

2.String方法

var str = "http://baidu.com"
str.capitalized  // 首字母大写

/// 使用String的方法
str.contains("o, swi") // 是否包含指定内容
str.hasPrefix("Hell") // 是否以指定的字符串开头
str.hasSuffix("ft")  // 是否以指定的字符串结尾

/// 可以使用hasPrefix() 和 hasSuffix() 方法做简单的验证
if (str.hasPrefix("http://") || str.hasPrefix("https://")) && (str.hasSuffix(".com") || str.hasSuffix(".cn")) {
    print("这是一个网址")
}

3.使用farmat定义一个字符串

let ss = String(format: "Hello")

4.NSString和String简单对比(由于在Swift中String里面的Index不是Int 类型，因此在使用的时候需要注意。如果习惯了Swift的风格，那么使用Index是更人性化的设计)

// NSString
var s3: NSString = "one third is 0.33"
s3.substring(from: 4)
s3.substring(to: 3)
s3.substring(with: NSMakeRange(0, 4))

// String
var s4: String = "one third is 0.33"
s4.substring(from: s4.index(s4.startIndex, offsetBy: 4))
s4.substring(to: s4.index(after: s4.index(s4.startIndex, offsetBy: 3)))
let range: Range = s4.startIndex..<s4.index(s4.startIndex, offsetBy: 4)

s4.substring(with: range)

5.获取某个下标后一个下标对应的字符

var string = "Hello-Swift"
//swift2.2
//var char = string[startIndex.successor()]
//swift3.0
var char = string[string.index(after: string.startIndex)]
var char1 = string[string.index(string.startIndex, offsetBy: 1)]

6.获取某个下标前一个下标对应的字符

//swift2.2
//var char2 = string[endIndex.predecessor()]
//swift3.0
var char2 = string[string.index(before: string.endIndex)]
var char22 = string[string.index(string.endIndex, offsetBy: -1)]

7.获取指定范围内的子字符串

//swift2.2
//var subString = string[startIndex...startIndex.advancedBy(4)]
//swift3.0
var subString = string[string.startIndex...string.index(string.startIndex, offsetBy: 4)]

//swift2.2
//var subString2 = string[endIndex.advancedBy(-5)...endIndex.predecessor()]
//swift3.0
var subString2 = string[string.index(string.endIndex, offsetBy: -5)..<string.endIndex]
var subString3 = string.substring(with: string.startIndex..<string.index(string.startIndex, offsetBy: 5))
var subString4 = string.substring(with: string.startIndex..<string.index(string.index(after: string.startIndex), offsetBy: 4))

8.获取子字符串在某个长字符串里面的范围

//swift2.2
//var range =  string.rangeOfString("Hello")
//swift3.0
var range1 = string.range(of: "Hello")
var range2 = string.rangeOfCharacter(from: CharacterSet.init(charactersIn: "H"))
let startInt = range1?.lowerBound   ///   0
let endInt = range1?.upperBound   ///    5

9.末尾追加字符串

//swift2.2
//string.appendContentsOf(" Hello-World")
//swift3.0
string.append("Hello-World")

10.指定位置插入字符和字符串
String-func-insert-contentsof_at_

//swift2.2
//string.insert("~", atIndex: string.startIndex.advancedBy(12))
//swift3.0
string.insert("~", at: string.index(string.startIndex, offsetBy: 12))
string.insert("~", at: string.endIndex)
// 这里需要注意 Collection -> ["r", "d"] 数组里面只能包含一个字符
// Collection where S.Iterator.Element == Character>(contentsOf newElements: S
string.insert(contentsOf: ["h","h"], at: string.index(string.startIndex, offsetBy: 10))

11.使用字符串替换指定范围的子字符串

//swift2.2
//string.replaceRange(string.startIndex...string.startIndex.advancedBy(4), with: "Hi")
//swift3.0
string.replaceSubrange(string.startIndex...string.index(string.startIndex, offsetBy: 4), with: "Hi")
string.replaceSubrange(string.startIndex..<string.index(string.startIndex, offsetBy: 2), with: "Sheriff")

12.在指定位置删除字符

//swift2.2
//string.removeAtIndex(string.endIndex.predecessor())
//swift3.0
string.remove(at: string.index(after: string.startIndex))
string.remove(at: string.index(before: string.endIndex))

13.删除指定范围的子字符串

//swift2.2
//string.removeRange(string.startIndex...string.startIndex.advancedBy(2))
//swift3.0
string.removeSubrange(string.startIndex...string.index(string.startIndex, offsetBy: 8))
string.insert("t", at: string.endIndex)

[参考]
开源中国
Swift文档