强引用循环
两个引用类型实例之间相互引用。
解决方式
实例之间的：
- Weak 引用。适用于一方的引用可为
nil的情形。
class Person {
let name: String
init(name: String) { self.name = name }
var apartment: Apartment?
}
class Apartment {
let number: Int
init(number: Int) { self.number = number }
weak var tenant: Person?
}
-
Unowned 引用。适用于一方的引用不能为
nil的情形。class Customer { let name: String var card: CreditCard? init(name: String) { self.name = name } } class CreditCard { let number: UInt64 unowned let customer: Customer init(number: UInt64, customer: Customer) { self.number = number self.customer = customer } } -
Unowned 引用和隐式解包的可选属性。适用于双方的引用都不能为
nil的情形。class Country { let name: String let capitalCity: City! init(name: String, capitalName: String) { self.name = name self.capitalCity = City(name: capitalName, country: self) } } class City { let name: String unowned let country: Country init(name: String, country: Country) { self.name = name self.country = country } }
闭包的（Capture List）：
在定义闭包时，添加一个列表，用来捕获产生循环的引用。
lazy var someClosure: (Int, String) -> String = {
[unowned self, weak someInstance] (index: Int, stringToProcess: String) -> String in
// closure body goes here
}
