'self' used before self.init call error while using NSCoding on a custom class

问题

I'm trying to encode a custom class so I can save it using NSKeyedArchiver.archivedDataWithRootObject

but when I try to conform to the NSCoding protocol, I get this error : 'self' used before self.init. Here is my code:

class MemberRewardsInfo: NSObject, NSCoding {
var id: Int?


  required convenience init?(coder aDecoder: NSCoder) {

    guard let unarchivedId = aDecoder.decodeObjectForKey("id") as? Int

      else {
        return nil
      } 
  }


  func encodeWithCoder(aCoder: NSCoder) {

    aCoder.encodeObject(id, forKey: "id")
  }
}

its pretty annoying, not sure why it's not working.

回答1:

The error message is sort of misleading, but you need to make init(coder:) a designated initializer.

You need to modify your init(code:) to something like this:

required init?(coder aDecoder: NSCoder) {
    guard let unarchivedId = aDecoder.decodeObjectForKey("id") as? Int else {
            return nil
    }
    self.id = unarchivedId
    super.init()
}

回答2:

Apparently it's upset about convenience. The assumption is that if you create a convenience initializer, it's going to chain to a "real initializer.

回答3:

When using a convenience initializer, just call the designated initializer, in your case, self.init(), inside block. See this example in Apple docs for an explanation.

required convenience init?(coder aDecoder: NSCoder) {
    guard let unarchivedId = aDecoder.decodeObjectForKey("id") as? Int

    else {
        return nil
    }
    self.init()
    self.id = unarchivedId

}

来源：https://stackoverflow.com/questions/38881755/self-used-before-self-init-call-error-while-using-nscoding-on-a-custom-class

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ios

swift

nscoding

nscoder