String

• Swift的字符串类型String,跟OC的NSString,在API设计上有很大差别.

         //空字符串
        var emptyStrin1 = ""
        var emptyStrin2 = String()
        
        var str = "123456"
        print(str.hasPrefix("123"))//true
        print(str.hasSuffix("456"))//true
        
        var string: String = "1"
        //拼接
        string.append("_2")//1_2
        //重载运算符 +
        string = string + "_3"//1_2_3
        //重载运算符 +=
        string += "_4"//1_2_3_4
        //\()字符串插值
        string = "\(string)_5"//1_2_3_4_5
        //长度:9,1_2_3_4_5
        print(string.count)

String的插入和删除

var str = "1_2"
        str.insert("_", at: str.endIndex)//1_2_
        str.insert(contentsOf: "3_4", at: str.endIndex)//1_2_3_4
        str.insert(contentsOf: "666", at: str.index(after: str.startIndex))//1666_2_3_4
        str.insert(contentsOf: "888", at: str.index(before: str.endIndex))//1666_2_3_8884
        str.insert(contentsOf: "hello", at: str.index(str.startIndex, offsetBy: 4))//1666hello_2_3_8884
        
        //@inlinable public func firstIndex(of element: Self.Element) -> Self.Index?
        //返回值为可选类型,字符串中没有"1",那么返回值为nil
        //这里确定肯定含有"1",所以强制解包
        //移除第一个"1"元素,如果字符串有多个"1",只移除第一个查找到的"1"
        str.remove(at: str.firstIndex(of: "1")!)
        print(str)//666hello_2_3_8884
        str.removeAll { (indexString) -> Bool in
            //如果该位置的字符为"6",那么返回true
            //该方法的作用移除str中所有"6"
            indexString == "6"
        }
        print(str)//hello_2_3_8884

        //等价写法
        str.removeAll {//字符串已经不包含"6"
            $0 == "6"
        }
        print(str)//hello_2_3_8884

        //hello_2_3_8884 长度为14 range = (14 - 4) ..< 14
        //10 ..< 14 ,从前面书第10个字符为_ 11: 8,12:8,13:8
        //所以移除的字符串为"_888"
        let range = str.index(str.endIndex, offsetBy: -4) ..< str.index(before: str.endIndex)
        str.removeSubrange(range)
        print(str)//hello_2_3_4

SubString

• string可以通过下标,prefix suffix等街区子串,子串类型不是String,而是Substring
• Substring和它的base共享字符串数据
• substring转为String时,会重新分配新的内存存储字符串数据

let str = "1_2_3_4_5"
        let sub1 = str.prefix(3)
        print(sub1)//1_2
        let sub2 = str.suffix(3)
        print(sub2)//4_5
        let range = str.startIndex ..< str.index(str.startIndex, offsetBy: 3)
        print(range)//Index(_rawBits: 1)..<Index(_rawBits: 196865)
        let sub3 = str[range]
        print(sub3)//1_2
        print(sub3.base)//1_2_3_4_5
        
        let str2 = String(sub3)
        print(str2)//1_2

String与Character

         for c in "jack" {//c 是Character类型
            print(c)
            print(type(of: c))//Character
        }

        let str = "jack"
        let c = str[str.startIndex]
        print(c)//j
        print(type(of: c))//Character
        

String的相关协议

• BidirectionalCollection 协议包含的部分内容
  1.startIndex endIndex属性,index方法
  2.String Array都遵守了这个协议
• RangeReplaceableCollection协议包含的部分内容
  1.append insert remove方法
  2.String Array都遵守了这个协议
• Dictionary Set也有实现上述协议中声明的一些方法,只是并没有遵守上述协议.

多行String

• 单引号修饰的多行字符串会报错,提示要使用"""

let str = "
        1
            "2"
        3
            '4'
        "

image.png

 override func viewDidLoad() {
        let str = """
        1
            "2"
        3
            '4'
        """
        print(str)
    } 
//打印结果:
1
    "2"
3
    '4'

• 如果要显示3引号,至少转义1个引号

override func viewDidLoad() {
        let str = """
        1 \"""
            "2" \"\""
        3 \"\"\"
            '4'
        """
        print(str)  
    } 
//打印结果:
1 """
    "2" """
3 """
    '4'

• 缩进以结尾的3引号为对齐线
  如下写法会报错.以结尾的3引号为对齐线之前的都报错.

  
  image.png
  

  修复后

class HomeViewController: UIViewController {
    override func viewDidLoad() {
        let str = """
        1
        2
        3
            4
        """
        print(str)
    } 
}
//打印结果
1
2
3
    4

• 以下字符串是等价的

let str1 = "111111111111"
        
        let str = """
        111111111111
        """
        print(str == str1)//true

String与NSString

• String与NSString之间可以随时的桥接转换
• 比较字符串内容是否等价
  1.String使用==运算符
  2.NSString使用isEqual方法,也可以使用 ==运算符.本质还是调用了isEqual方法

        let str1: String = "jack"
        let str2: NSString = "rose"
        print(str1)
        print(str2)
        let str3 = str1 as NSString
        let str4 = str2 as String
        print(str3)
        print(str4)
        
        //ja
        let str5 = str3.substring(with: NSRange(location: 0, length: 2))
        print(str5)

        let str1: String = "jack"
        let str2: NSString = "jack"
       
        print(str2 as String == str1)//true
        print(str1 == str2 as String)//true
        print(str2.isEqual(to: str1))//true
        print(str2.isEqual(str1))//true
        print(str1.isEqual(str2))//true

Swift OC桥接转换表

String	<-->	NSString
String	<--	NSMutableString
Array	<-->	NSArray
Array	<--	NSMutableArray
Dictionary	<-->	NSDictionary
Dictionary	<--	NSMutableDictionary
Set	<-->	NSSet
Set	<--	NSMutableSet