Swift之关联对象

在swift中，展不能添加存储属性，Swift中可以使用Objective-C的关联对象(Associated Objects)的方式添加属性，弥补这一痛点
1、objc_setAssociatedObject

2、objc_getAssociatedObject

3、objc_removeAssociatedObjects

需要注意的是：objc_removeAssociatedObjects会删除对象关联的所有属性，所以可能导致把一些非自己添加的关联属性也删除掉。如果要删除某属性，使用objc_setAssociatedObject将value设置为nil即可

extension User {
    private static var AGE_KEY:Bool = false
    private static var WEIGHT_KEY: Bool = false
    var newAge:Int {
        get{
            objc_getAssociatedObject(self, &Self.AGE_KEY) as? Int ?? 0
        }
        set(n){
            objc_setAssociatedObject(self, &Self.AGE_KEY, n, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
    var address: String {
        get{
            objc_getAssociatedObject(self, &Self.WEIGHT_KEY) as? String ?? "暂无地址"
        }
        set{
            objc_setAssociatedObject(self, &Self.WEIGHT_KEY, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
    
    func removeAll() {
        objc_removeAssociatedObjects(self)
    }
    
    func removeAge() {
        objc_setAssociatedObject(self, &Self.AGE_KEY, nil, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
    }
}

使用：

        let u = User()
        print(u.newAge)
        print(u.address)
        u.newAge = 10
        u.address = "address"
        print(u.newAge)
        print(u.address)
        
        u.removeAge()
        print(u.newAge)
        print(u.address)
        
        u.removeAll()
        print(u.newAge)
        print(u.address)

打印结果：

0
暂无地址
10
address
0
address
0
暂无地址