去gayhub上瀏覽大佬的代碼
struct Landmark: Hashable, Codable, Identifiable {
...
}
此時萌新的表情是這樣的
0.jpeg
奧不對夕凝，是這樣的
1.jpeg
今天我們就仔細分析下這幾個秕硝。。往扔。是干啥用的
首先 - Hashable
You can use any type that conforms to the Hashable protocol in a set or as a dictionary key.
只有遵循了Hashable 協(xié)議 才能被添加到 Set 中 或者用作 Dictionary 的 key 值
舉個例子
// 假如我們有一個Person類
struct Person {
var name: String
var age: Int
}
// 假如我們有兩位同學 小明 和 小紅
let ming = Person(name: "ming", age: 10)
let hong = Person(name: "hong", age: 11)
// 現(xiàn)在我們有一個需求 1.把他加入到一個Set中 2. 用作Dictionary的key
// 我們這樣寫
var set: Set<Person> = [] //報錯 Type 'Person' does not conform to protocol 'Hashable'
set.insert(ming)
set.insert(hong)
print(set)
var dic: [Person: String] = [:] //報錯 Type 'Person' does not conform to protocol 'Hashable'
dic[ming] = ming.name //報錯 Referencing subscript 'subscript(_:)' on 'Dictionary' requires that 'Person' conform to 'Hashable'
dic[hong] = hong.name //報錯 Referencing subscript 'subscript(_:)' on 'Dictionary' requires that 'Person' conform to 'Hashable'
print(dic)
// 由于我們的Person并沒有遵循Hashable協(xié)議旋膳，所以以上代碼會報錯
// 接下來 我們修改Person
struct Person: Hashable {
var name: String
var age: Int
}
// 修改之后 澎语，以上報錯會消失
// 打印結(jié)果為 set ---- [Test0.Person(name: "hong", age: 11), Test0.Person(name: "ming", age: 10)]
// dic --- [Test0.Person(name: "ming", age: 10): "ming", Test0.Person(name: "hong", age: 11): "hong"]
- 拓展
// 假如我們的Person是一個Class而不是Struct，就必須要實現(xiàn)Hashable的協(xié)議方法
class Person: Hashable {
// Hashable 繼承自 Equatable, 此方法為Equatable的協(xié)議方法验懊， 用來比較兩個對象是否協(xié)議相等擅羞， 返回true的話 在Set或者Dictionary中都會被認為是同一個對象（在Set中會被去重， 在Dictionary中覆蓋之前的值）
static func == (lhs: Person, rhs: Person) -> Bool {
return lhs.name == rhs.name && lhs.age == rhs.age
}
func hash(into hasher: inout Hasher) {
hasher.combine(name)
hasher.combine(age)
}
init(name: String, age: Int) {
self.name = name
self.age = age
}
var name: String
var age: Int
}
舉個栗子
// 還是之前的小明和小紅
let ming = Person(name: "ming", age: 10)
let hong = Person(name: "hong", age: 11)
var set: Set<Person> = []
set.insert(ming)
set.insert(hong)
print(set) // [Test0.Person, Test0.Person]
var dic: [Person: String] = [:]
dic[ming] = ming.name
dic[hong] = hong.name
print(dic) // [Test0.Person: "hong", Test0.Person: "ming"]
// 因為ming1.name == ming.name && ming1.age == ming.age Person 的 static func == (lhs: Person, rhs: Person) -> Bool 方法成立 ming1 會覆蓋之前的 ming
let ming1 = Person(name: "ming", age: 10)
set.insert(ming1)
dic[ming1] = ming1.name
print(set) // [Test0.Person, Test0.Person]
print(dic) // [Test0.Person: "hong", Test0.Person: "ming"]
// // 因為ming2.name == ming1.name && ming2.age == ming1.age Person 的 static func == (lhs: Person, rhs: Person) -> Bool 方法不成立 ming2 不會會覆蓋之前的 1ming
let ming2 = Person(name: "ming", age: 20)
set.insert(ming2)
dic[ming2] = ming2.name
print(set) // [Test0.Person, Test0.Person, Test0.Person]
print(dic) // [Test0.Person: "hong", Test0.Person: "ming", Test0.Person: "ming"]
假如我們對Person進行修改 , 年齡相同就當做同一個人
class Person: Hashable {
static func == (lhs: Person, rhs: Person) -> Bool {
// return lhs.name == rhs.name && lhs.age == rhs.age
return lhs.age == rhs.age
}
func hash(into hasher: inout Hasher) {
// hasher.combine(name)
hasher.combine(age)
}
init(name: String, age: Int) {
self.name = name
self.age = age
}
var name: String
var age: Int
}
// 還是之前的小明和小紅
let ming = Person(name: "ming", age: 10)
let hong = Person(name: "hong", age: 11)
var set: Set<Person> = []
set.insert(ming)
set.insert(hong)
print(set) // [Test0.Person, Test0.Person]
var dic: [Person: String] = [:]
dic[ming] = ming.name
dic[hong] = hong.name
print(dic) // [Test0.Person: "hong", Test0.Person: "ming"]
// 因為ming1.age == ming.age Person 的 static func == (lhs: Person, rhs: Person) -> Bool 方法成立 ming1 會覆蓋之前的 ming
let ming1 = Person(name: "ming", age: 10)
set.insert(ming1)
dic[ming1] = ming1.name
print(set) // [Test0.Person, Test0.Person]
print(dic) // [Test0.Person: "hong", Test0.Person: "ming"]
// // 因為 ming2.age == ming1.age Person 的 static func == (lhs: Person, rhs: Person) -> Bool 方法成立 ming2 會覆蓋之前的 1ming
let ming2 = Person(name: "aming", age: 10)
set.insert(ming2)
dic[ming2] = ming2.name
print(set) // [Test0.Person, Test0.Person, Test0.Person]
print(dic) // [Test0.Person: "hong", Test0.Person: "aming"]
其次 - Codable
在swift4之前义图，swift中數(shù)據(jù)解析的方式大都采用OC的KVC機制减俏，swift4后可以采用Codable直接將json轉(zhuǎn)成對象
先看定義
public typealias Codable = Decodable & Encodable
json轉(zhuǎn)對象
struct Person: Codable {
var name: String
var age: Int
}
let jsonStr = "{\"name\" : \"ming\", \"age\" : 10}"
guard let jsonData = jsonStr.data(using: .utf8) else {
exit(0)
}
let decoder = JSONDecoder()
guard let obj = try? decoder.decode(Person.self, from: jsonData) else {
exit(0)
}
print(obj.name) // ming
print(obj.age) // 10
當json中的key值與我們定義的屬性名對應(yīng)時可以采用上述簡單的方法， 如果不對應(yīng)的話就需要借助CodingKeys來實現(xiàn)
// 修改Person
struct Person: Codable {
var name: String
var age: Int
enum CodingKeys: String, CodingKey {
case name = "a_name"
case age = "age" //如果前后一致的話 可以省略=以及后邊的部分 如 case age, 如果有需要忽略的key, 則不寫到此處便可
}
}
let decoder = JSONDecoder()
let jsonStr1 = "{\"a_name\" : \"ming\", \"age\" : 10}"
guard let jsonData1 = jsonStr1.data(using: .utf8) else {
exit(0)
}
guard let obj1 = try? decoder.decode(Person.self, from: jsonData1) else {
exit(0)
}
print(obj1.name) // ming
print(obj1.age) // 10
第三 - CaseIterable
swift4.2之后引進CaseIterable, 用于合成簡單枚舉類型的allCases靜態(tài)屬性
舉個栗子
enum Week: CaseIterable {
case Sun
case Mon
case Tue
case Wen
case Thu
case Fri
case Sat
}
print(Week.allCases) // [Test0.Week.Sun, Test0.Week.Mon, Test0.Week.Tue, Test0.Week.Wen, Test0.Week.Thu, Test0.Week.Fri, Test0.Week.Sat]
我們也可以重寫allCases方法 例如
enum Week: CaseIterable {
case Sun
case Mon
case Tue
case Wen
case Thu
case Fri
case Sat
static var allCases: [Week] {
return [.Mon, .Tue, .Wen, .Thu, .Fri, Sat, Sun]
}
}
print(Week.allCases) //[Test0.Week.Mon, Test0.Week.Tue, Test0.Week.Wen, Test0.Week.Thu, Test0.Week.Fri, Test0.Week.Sat, Test0.Week.Sun]
ming
至于 - Identifiable
1.jpeg
完全沒搞懂呀, 僅僅是遵循了這個協(xié)議之后就必須有一個名為id的屬性嗎碱工？然后呢娃承。。怕篷。
