Swift中的强引用和弱引用

6 回答

• 10

  默认情况下属性很强，但如果你想要一个弱属性，你可以：

  weak var tenant: Person?
  

  资料来源：https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/AutomaticReferenceCounting.html

  回复于 2024-04-18T22:41:23+08:00
• 3

  只是想让你知道默认情况下var是强的，但是通过在它前面添加“弱”你会使它变弱 . 以防你错过了它

  回复于 2024-04-18T22:41:23+08:00
• 61

  直接从Swift Language guide：

  class Person {
      let name: String
      init(name: String) { self.name = name }
      var apartment: Apartment?
      deinit { println("\(name) is being deinitialized") }
  }
  
  class Apartment {
      let number: Int
      init(number: Int) { self.number = number }
      weak var tenant: Person?
      deinit { println("Apartment #\(number) is being deinitialized") }
  }
  

  默认情况下属性很强 . 但是看看“公寓”这个类的租户属性，它被宣称为弱者 . 您还可以使用unowned关键字，该关键字转换为Objective-C中的unsafe_unretained

  https://itunes.apple.com/tr/book/swift-programming-language/id881256329?mt=11

  回复于 2024-04-18T22:41:23+08:00
• 0

  默认情况下，var很强 . 您可以在var之前添加weak关键字以使其变弱 .

  回复于 2024-04-18T22:41:23+08:00
• 4

  这是一个重要的评论，但我无法适应它 .

  如果你这样做

  weak let name : SomeClass
  

  它会给出以下错误：

  'weak'必须是一个可变变量，因为它可能在运行时发生变化

  你必须这样做

  weak var name : SomeClass
  

  'weak'变量应该有可选类型'SomeClass？'

  所以你必须这样做：

  weak var name : SomeClass?
  

  此外，在Swift中，所有弱引用都是非常量的Optionals（想想var与let），因为当没有任何东西持有强引用时，引用可以并且将被突变为nil . 见here

  由于这种强制性的可选化，您始终需要打开它以便可以访问其实际值 .

  回复于 2024-04-18T22:41:23+08:00
• 11

  详情

  xCode 9.1，Swift 4

  有关ARC使用的更多信息

  • Kaan Dedeoglu回答

  • ARC and Memory Management in Swift

  • "WEAK, STRONG, UNOWNED, OH MY!" - A GUIDE TO REFERENCES IN SWIFT

  • ARC Swift Tutorial

  完整样本

  import UIKit
  
  var str = "Hello, playground"
  
  class BasicClass: CustomStringConvertible {
      let text: String
      init(text: String) { self.text = text }
      deinit { print ("Object of the \"\(className)\" class deinited") }
  
      var className: String {
          return "\(type(of: self))"
      }
  
      var referenceCount: Int {
          return CFGetRetainCount(self)
      }
      var description: String {
          return "className: \(className), reference count: \(referenceCount)"
      }
  }
  
  class Class1: BasicClass {
      var objectWithStrongReference: Class2?
      override var description: String {
          return super.description + ", embed strong obj reference count: \(objectWithStrongReference?.referenceCount ?? 0)"
      }
  }
  
  class Class2: BasicClass {
      weak var objectWithWeakReference: Class1?
      override var description: String {
          return super.description + ", embed weak obj reference count: \(objectWithWeakReference?.referenceCount ?? 0)"
      }
  }
  
  var obj1: Class1? = Class1(text: "String 1")
  print(obj1 ?? "nil")
  var obj2: Class2? = Class2(text: "String 2")
  print(obj2 ?? "nil")
  
  print("=====================================")
  print("obj1.value = obj2, obj2.value = obj1")
  obj1?.objectWithStrongReference = obj2
  obj2?.objectWithWeakReference = obj1
  print(obj1 ?? "nil")
  print(obj2 ?? "nil")
  print("=====================================")
  print("obj2 = nil")
  obj2 = nil
  print(obj1 ?? "nil")
  print(obj2 ?? "nil")
  
  print("=====================================")
  print("obj1 = nil")
  obj1 = nil
  print(obj1 ?? "nil")
  print(obj2 ?? "nil")
  

  结果

  

  回复于 2024-04-18T22:41:23+08:00