【学习】重学Swift5-错误处理、三方库等

九、其他话题

1. 错误处理

   enum VendingMachineError: Error {
       case invalidSelection
       case insufficientFunds(coinsNeed: Int)
       case outOfStock
   }
   
   
   struct Item {
       var price: Int
       var count: Int
   }
   
   class VendingMachine {
       var inventory = [
           "Candy Bar": Item.init(price:12, count: 7),
           "Chips": Item.init(price: 20, count: 0),
           "Bread": Item.init(price:15, count:5)
       ]
       
       var coinsDecposited = 0
       
       func vend(itemName: String) throws {
           
           defer {
               print("推出清理")
           }
           print("开始售卖")
           
           guard let item = inventory[itemName] else {
               throw VendingMachineError.invalidSelection
           }
           
           guard item.count > 0 else {
               throw VendingMachineError.outOfStock
           }
           
           guard coinsDecposited >= item.price else {
               throw VendingMachineError.insufficientFunds(coinsNeed: item.price)
           }
           
           coinsDecposited -= item.price
           var newItem = item
           newItem.count -= 1
           inventory[itemName] = newItem
           print("售卖成功")
           
       }
   }
   
   
   var machine = VendingMachine()
   machine.coinsDecposited = 5
   
   do {
       try machine.vend(itemName: "Chips")
   } catch VendingMachineError.invalidSelection {
       print("没有当前商品")
   } catch VendingMachineError.insufficientFunds(let coinsNeeded) {
       print("你需要投\(coinsNeeded)币")
   } catch VendingMachineError.outOfStock {
       print("已售空")
   } catch {
       print("未知错误")
   }
   
   // throw 抛出异常 do-catch处理异常 defer
   

2. 权限控制

   // open  public internal  fileprivate  private
   /*
   1.类成员的访问级别不能高于类的访问级别；
   2.常量、变量、属性、下标脚本访问级别低于其所声明的类型级别，并且如果不是默认访问级别（internal）要明确声明访问级别。
   3.在不违反1、2的情况下，setter的访问级别可以抵御getter的访问级别。
   4.必要构造方法（required修饰）的访问级别必须和类访问级别相同，狗狗剃的默认逐一构造函数的访问级别不高于其成员的访问级别，其他方法的访问级别遵循规则1
   */
   

3. 不透明类型

4. 自动引用计数

   // 循环引用
   // 弱引用weak(对生命周期中引用会变为nil的实例，只能声明变量类型)  无主引用unowned(对初始化赋值之后引用再也不会赋值为nil的实例，无主引用默认始终有值，只能定义为非可选类型) 
   
   // 闭包的循环引用
   lazy var someColisure = {
      [unowned self, weak delegate = self.delegate](index: Int, stringToProgress: String) -> String in
     // code 
   }
   

5. 内存安全

十、常见三方库

Alamofire  SwiftJSON  R.Swift  MonkeyKing  Kingfisher  SnnapKit  Dollar

十一、加餐

1.可选链、

2.KVC
· 继承自NSObject的类，标记@objc的属性可以使用setValue:(_ forKey:)
· 非继承自NSObject的类和结构体，使用索引+参数值
struct ValueType {
    var name: String
}

var object = ValueType.init(name: "Objective-c")

// set
object[keyPath: \ValueType.name] = "swift"
// get
let valueOfName = object[keyPath: \ValueType.name]
print(valueOfName)

3.KVO
// 只有NSObject才能支持KVO，且要观察的属性必须使用@objc dynamic修饰
// 方法一
class Person: NSObject {
    @objc dynamic var age = 0
}

class ViewController: UIViewController {

    let p = Person()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        p.addObserver(self, forKeyPath: "age", options: [.new, .old], context: nil)
        
        p.age = 33
        // Do any additional setup after loading the view.
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == "age" {
            print(change as Any)
        }
    }

}

// 方法二
class Person: NSObject {
    @objc dynamic var age = 0
}

class ViewController: UIViewController {

    @objc dynamic let p = Person()
    
    var ob: NSKeyValueObservation?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        self.ob = observe(\.p.age, options: [.new, .old], changeHandler: { (_ , change) in
            print(change as Any)
        })
        
        p.age = 33
        // Do any additional setup after loading the view.
    }

}