swift 设计模式之-责任链模式

 

1. //每个对象持有对下一个对象的引用，这样就会形成一条链，请求在这条链上传递，直到某一对象决定处理该请求。但是发出者并不清楚到底最终那个对象会处理该请求，所以，责任链模式可以实现，在隐瞒客户端的情况下，对系统进行动态的调整。
2. 如下关于一个ATM取款机的例子，来告知是否可以取款到相应金额。
3. final class MoneyPil{
4.     let value : Int
5.     var quantity:Int
6.     var nextPile:MoneyPil?
7.     init(value:Int,quantitly:Int,nextpile:MoneyPil?) {
8.         self.value = value
9.         self.quantity = quantitly
10.         self.nextPile = nextpile
11.     }
12.  
13.     func canWithDraw(amount:Int) -> Bool {
14.         var amount = amount
15.         func canTakeSomeBill(want:Int)->Bool{
16.             return (want/self.value)>0}
17.         var quantity = self.quantity
18.         while canTakeSomeBill(want: amount) {
19.             if quantity == 0{break}
20.             amount -= self.value
21.             quantity -= 1
22.         }
23.             guard amount > 0 else{return true}
24.             if let next = self.nextPile{
25.                 return next.canWithDraw(amount:amount)
26.             }
27.             return false
28.     }
29. }
30. final class ATM {
31.     private var hundred:MoneyPil
32.     private var fifty:MoneyPil
33.     private var twenty:MoneyPil
34.     private var ten:MoneyPil
35.     private var startoile:MoneyPil{
36.         return self.hundred
37.     }
38.     init(hundred: MoneyPil,
39.            fifty: MoneyPil,
40.           twenty: MoneyPil,
41.              ten: MoneyPil) {
42.         self.hundred = hundred
43.         self.fifty   = fifty
44.         self.twenty  = twenty
45.         self.ten     = ten
46.     }
47.     func canWithDraw(amount:Int)->String{
48.         return "Can withdraw:\(self.startoile.canWithDraw(amount: amount))"
49.     }

1. }
2. let ten = MoneyPil(value:10, quantitly:6, nextpile: nil)
3. let twenty = MoneyPil(value: 20, quantitly: 2, nextpile: ten)
4. let fifty = MoneyPil(value: 50, quantitly: 2, nextpile: twenty)
5. let hundred = MoneyPil(value: 100, quantitly: 1, nextpile: fifty)

1. var atm = ATM(hundred: hundred, fifty: fifty, twenty: twenty, ten: ten)
2. atm.canWithDraw(amount: 100)
3. atm.canWithDraw(amount: 310)
4. atm.canWithDraw(amount: 165)
5. atm.canWithDraw(amount: 70)