NSCoding在Swift中的继承类中需要初始化器 [英] NSCoding required initializer in inherited classes in Swift

问题描述

我有类Foo，它符合 NSObject 和 NSCoding c $ c> NSKeyedArchiver 我想创建类Bar，Foo的子类，也将符合 NSObject 和 NSCoding 。我有一个问题，了解如何在子类中创建所需的方便初始化？（coder aDecoder：NSCoder）

I have class Foo which conforms to NSObject and NSCoding which I want to be able to persist with NSKeyedArchiver I want to create class Bar, a subclass of Foo that will also conform to NSObject and NSCoding. I am having a problem understanding how to create the required convenience init?(coder aDecoder: NSCoder) in the subclass.

class Foo ...

so class Foo...

class Foo: NSObject, NSCoding {
  let identifier:String
  init(identifier:String) {
    self.identifier = identifier
  }

  override var description:String {
    return "Foo: \(identifier)"
  }

  func encodeWithCoder(aCoder: NSCoder) {
    aCoder.encodeObject(identifier, forKey: "identifier")
  }

  required convenience init?(coder aDecoder: NSCoder) {
    guard let identifier = aDecoder.decodeObjectForKey("identifier") as? String
      else {
        return nil
    }
    self.init(identifier:identifier)
  }
}

然后类Bar ...

Then class Bar ...

class Bar:Foo {
  let tag:String

  init(identifier:String, tag:String) {
    self.tag = tag
    super.init(identifier: identifier)
  }

  override var description:String {
    return "Bar: \(identifier) is \(tag)"
  }
}

我可以通过添加以下方法来编译这个 NSCoding 符合

I can get this to compile by adding the following methods on to make this NSCoding compliant

  override func encodeWithCoder(aCoder: NSCoder) {
    aCoder.encodeObject(tag, forKey: "tag")
    super.encodeWithCoder(aCoder)
  }

这是有道理的，因为我调用 super.encodeWithCoder（...）重用超级使这个DRY。我所遇到的问题是创建 required convenience init？（...）唯一的方法，我似乎得到它编译是通过这样做...

this makes sense because I call super.encodeWithCoder(...) reusing the super makes this DRY. The problem I am having is creating the required convenience init?(...) the only way I can seem to get it to compile is by doing this...

  required convenience init?(coder aDecoder:NSCoder) {
    guard let identifier = aDecoder.decodeObjectForKey("identifier") as? String,
          let tag        = aDecoder.decodeObjectForKey("tag") as? String
      else {
        return nil
    }

    self.init(identifier:identifier, tag:tag)
  }

我基本上已经复制了超类所需的初始化程序，然后为子类属性添加了额外的解码方法。这种方法似乎不正确...

I basically have copied the superclass required initializer and then added the additional decode method for the subclass property. This approach does not seem correct...

有更好的方法来实现这个？

Is there a better way to implement this??

推荐答案

我在playground尝试了代码，当我勾选错误的红色圆圈时，它只是自动添加代码。

I have try your code in playground, it just auto to add the code when I tick the red circle of the Error.

代码就像您的函数所需的方便init。

The coding is like your function required convenience init.

示例代码：

required convenience init?(coder aDecoder: NSCoder)
{
    fatalError("init(coder:) has not been implemented")
}

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