swift - 初始化阶段 - 这可以更容易地完成吗？

Question

我有一个实现 MultipeerConnectivity 的类，我想要一个子类来为广告商实现它。这是我想要的:

class ConnectionManager: NSObject {

  let serviceType: String
  let peerID: MCPeerID
  let session: MCSession
  var delegate: ViewController!

  override init() {
    serviceType = "mc-service"
    peerID = MCPeerID(displayName: UIDevice.current.name)
    session = MCSession(peer: peerID, securityIdentity: nil, encryptionPreference: .required)
    super.init()
    session.delegate = self
  }
}

class AdvertiserConnectionManager: ConnectionManager {

  let assistant: MCAdvertiserAssistant

  override init() {
    assistant = MCAdvertiserAssistant(serviceType: serviceType, discoveryInfo: nil, session: session)
    super.init()
    assistant.delegate = self
    assistant.start()
  }
}

但这打破了 init() 的分阶段规则，因为 MCAdvertiserAssistant(serviceType:, discoveryInfo:, session:) 使用了 serviceType 和 session , 父类(super class)的两个属性。

我已经用子类完成了以下操作，通过懒惰地声明 assistant 作弊。这行得通!为什么？初始化器仍然需要调用self!!!我不得不做这种不自然的事情来创建我的子类。而且我可能已经颠覆了分阶段旨在避免的事情!!

class AdvertiserConnectionManager: ConnectionManager {

  lazy var assistant: MCAdvertiserAssistant = {
    MCAdvertiserAssistant(serviceType: serviceType, discoveryInfo: nil, session: session)
  }()

  override init() {
    super.init()
    assistant.delegate = self
    assistant.start()
  }
}  

Answer 1

你不是作弊，这不是一件不自然的事情。这是初始化相互依赖的对象属性的常用方法。

来自documentation (Swift Language Guide: Properties) :

A lazy stored property is a property whose initial value is not calculated until the first time it is used.
...
Lazy properties are useful when the initial value for a property is dependent on outside factors whose values are not known until after an instance’s initialization is complete.

在您的情况下，assistant 将在 super.init 调用之后 初始化，当 self 时， serviceTime 和 session 有效且可用。