Swift 父类与子类的转化

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1.创建一个父类食物(Food),及子类苹果(Apple)与可乐(coke)

class Food {

var name = ""

init(footName: String) {

name = footName

}

func Nickname() {

print("I am an \(name)")

}

class Apple: Food {

var footType = ""

override func Nickname() {

print("I am an \(name),I tried \(footType) ")

}

class Coke: Food {

var footType = ""

override func Nickname() {

print("I am an \(name),I tried \(footType) ")

}

------------------------------------------------* 我是一条分割线 * ---------------------------------------------

overridefunc viewDidLoad() {

super.viewDidLoad()

// 1.子类对象转化为父类对象

let food_Apple:Food =Apple(footName:"Apple")

food_Apple.Nickname()

let food_Coke:Food =Coke(footName:"Coca-Cola")

food_Coke.Nickname()

// 2，父类对象转为子类对象 as! as?

//父类转化为子类需要使用 as!如果当前父类是由子类对象转化过来的，那么同样可以转化回去。

let apple = food_Appleas!Apple

apple.footType ="Green foot"

apple.Nickname()

let coke = food_Cokeas!Coke

coke.footType ="Junk food"

coke.Nickname()

//如果当前转化的子类的对象的父类，并不是有改子类转化成的父类，则会报错

//如果我们需要将当前父类对象转为子类对象但是并不确定当前对象是否为子类对象转化过来的，该如何处理？ Swift为我们提供一个方法 as?

iflet a = food_Appleas?Apple {

a.footType ="Green foot"

a.Nickname()

print("子类对象")

} else {

print("非子类对象")

}

if let a1 = food_Coke as?Coke {

a1.footType ="Junk food"

a1.Nickname()

print("子类对象")

} else {

print("非子类对象")

}

// 3 也可以通过is判读返回一个Bool值

print(food_AppleisApple)

}

代码：

class ClassViewController: UIViewController {    override func viewDidLoad() {        super.viewDidLoad()        // Do any additional setup after loading the view.        // 1.子类对象转化为父类对象        let food_Apple: Food = Apple(footName: "Apple")        food_Apple.Nickname()                let food_Coke: Food = Coke(footName: "Coca-Cola")        food_Coke.Nickname()                // 2，父类对象转为子类对象 as!   as?        // 父类对象转化为子类对象，父类转化为子类需要使用 as! 如果当前对象是父类对象，但是他如果是子类对象转化过来的，那么可以转化回去                let apple = food_Apple as! Apple        apple.footType = "Green foot"        apple.Nickname()                let coke = food_Coke as! Coke        coke.footType = "Junk food"        coke.Nickname()                // 如果当前转化的子类的对象的父类，并不是有改子类转化成的父类，则会报错                // 如果我们需要将当前父类对象转为子类对象但是并不确定 当前对象是否为子类对象转化过来的，该如何处理？ Swift为我们提供一个方法 as?        if let a = food_Apple as? Apple {            a.footType = "Green foot"            a.Nickname()            print("子类对象")        } else {            print("非子类对象")        }                if let a1 = food_Coke as? Coke {            a1.footType = "Junk food"            a1.Nickname()            print("子类对象")        } else {            print("非子类对象")        }                // 3 如何判断某一个对象是不是这个类的对象 可以 使用 对象 is 类 来判断        // 我们会发现判断子类对象是不是父类对象返回也是true        print(food_Apple is Apple)    }    override func didReceiveMemoryWarning() {        super.didReceiveMemoryWarning()    }}class Food {    var name = ""    init(footName: String) {        name = footName    }        func Nickname() {        print("I am an \(name)")    }}class Apple: Food {    var footType = ""    override func Nickname() {        print("I am an \(name),I tried \(footType) ")    }}class Coke: Food {    var footType = ""    override func Nickname() {        print("I am an \(name),I tried \(footType) ")    }}

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