1.存儲類型的屬性的初始化

• 存儲類型

struct YXRect {
    var origin:CGPoint
    var width:CGFloat
    var height:CGFloat
}

• 存儲類型的屬性的初始化,存儲類型的屬性，在結(jié)構(gòu)體或者對象創(chuàng)建的時候必須保證初始化一次
• 在初始化方法中初始化,在聲明的時候沒有初始化，那么在init函數(shù)中就是必須有的

//錯誤
//class YXRect {
//    var origin:CGPoint
//    var width:CGFloat
//    var height:CGFloat
//    init(width:CGFloat,height:CGFloat){
//        self.width = width
//        self.height = height
//    }
//}
class YXRect {
      var origin:CGPoint
      var width:CGFloat
      var height:CGFloat
      init(origin:CGPoint,width:CGFloat,height:CGFloat){
          self.origin = origin
          self.width = width
          self.height = height
      }
}

• 直接在聲明的時候初始化,在聲明的時候有初始化的，在init函數(shù)中就不是必須的了

class YXRect {
      var origin:CGPoint = CGPoint(x:1,y:1)
      var width:CGFloat
      var height:CGFloat
      init(width:CGFloat,height:CGFloat){
          self.width = width
          self.height = height
      }
  }

• optional屬性不強(qiáng)制初始化

//正確
class YXRect {
    var origin:CGPoint?
    var width:CGFloat
    var height:CGFloat
    init(width:CGFloat,height:CGFloat){
        self.width = width
        self.height = height
    }
}

• struct會默認(rèn)提供全部屬性的init函數(shù)，而class不會

struct YXRect {
    var origin:CGPoint
    var width:CGFloat
    var height:CGFloat
}
//錯誤
//class YXRect4 {
//    var origin:CGPoint
//    var width:CGFloat
//    var height:CGFloat
//
//}
class YXRect{
    var origin:CGPoint
    var width:CGFloat
    var height:CGFloat
    init(origin:CGPoint,width:CGFloat,height:CGFloat){
        self.origin = origin
        self.width = width
        self.height = height
    }
}

2.存儲類型屬性的監(jiān)聽

struct YXRect {
    var origin:CGPoint
    var width:CGFloat{
        willSet(newValue){
            print("will set \(newValue)")
        }
        didSet(newValue){
            print("did set \(newValue)")
            if(newValue>200){
                width = 200
            }
        }
    }
    var height:CGFloat
    init(origin:CGPoint,width:CGFloat,height:CGFloat){
        self.origin = origin
        self.width = width
        self.height = height
    }
}

3.計算類型的屬性

• 計算屬性的獲取

struct YXRect {
    var origin:CGPoint
    var width:CGFloat
    var height:CGFloat
    
    init(origin:CGPoint,width:CGFloat,height:CGFloat){
        self.origin = origin
        self.width = width
        self.height = height
        
    }
    //只有獲取的時候不需要加上get關(guān)鍵字
    var center : CGPoint  {
        print("獲取center")
        let x = self.origin.x + self.width*0.5
        let y = self.origin.y + self.height * 0.5
        return CGPoint(x:x,y:y)
    }
}

• 計算屬性的設(shè)置

struct YXRect {
    var origin:CGPoint
    var width:CGFloat
    var height:CGFloat
    
    init(origin:CGPoint,width:CGFloat,height:CGFloat){
        self.origin = origin
        self.width = width
        self.height = height
        
    }
    //有獲取，也有設(shè)置就需要加上get 和 set方法
    var center : CGPoint  {
        get{
            print("獲取center2")
            let x = self.origin.x + self.width*0.5
            let y = self.origin.y + self.height * 0.5
            return CGPoint(x:x,y:y)
        }
        set(newValue){
            print("設(shè)置center2")
            self.origin.x = newValue.x - self.width * 0.5
            self.origin.y = newValue.y - self.height * 0.5
        }   
    }
}

4.懶加載屬性

class Account{
    var name : String
    //懶加載屬性的self容易造成鏈循環(huán)，從而導(dǎo)致self不能釋放，此處應(yīng)使用unowned
    lazy var hellow :String = {[unowned self] in
        print("初始化拉")
        return "hellow \(self.name)"
        }()
    init(name:String){
        self.name = name
    }
}

var accout = Account(name:"aaa")
accout.hellow
accout.hellow
accout.hellow
//"初始化啦"只打印一次

5.類的靜態(tài)屬性

Swift中可以像java一樣在一個類中聲明一個靜態(tài)變量
而OC必須借助類方法才能達(dá)到這樣的效果

• Swift

class Person {
    static var type = "地球人"
}
//這樣就可以直接訪問
Person.type   //地球人

• OC

@interface Person : NSObject
 +(NSString *)type;
@end
@implementation Person
static NSString *type = @"地球人";
+(NSString *)type{
    return type;
}
@end
[Person type];

可見相比較而言還是Swift語法，更加簡練一些。