Swift：不符合协议NSCoding

Question

我试图在我用swift编写的类上使用NSCoding协议，但似乎无法弄清楚为什么当我实现所需的方法时编译器抱怨它“不符合协议NSCoding”：

class ServerInfo: NSObject, NSCoding {

    var username = ""
    var password = ""
    var domain = ""
    var location = ""
    var serverFQDN = ""
    var serverID = ""

    override init() {

    }

    init(coder aDecoder: NSCoder!) {
        self.username = aDecoder.decodeObjectForKey("username") as NSString
        self.password = aDecoder.decodeObjectForKey("password") as NSString
        self.domain = aDecoder.decodeObjectForKey("domain") as NSString
        self.location = aDecoder.decodeObjectForKey("location") as NSString
        self.serverFQDN = aDecoder.decodeObjectForKey("serverFQDN") as NSString
        self.serverID = aDecoder.decodeObjectForKey("serverID") as NSString
    }


    func encodeWithCoder(_aCoder: NSCoder!) {
        _aCoder.encodeObject(self.username, forKey: "username")
        _aCoder.encodeObject(self.password, forKey: "password")
        _aCoder.encodeObject(self.domain, forKey: "domain")
        _aCoder.encodeObject(self.location, forKey: "location")
        _aCoder.encodeObject(self.serverFQDN, forKey: "serverFQDN")
        _aCoder.encodeObject(self.serverID, forKey: "serverID")
    }

}

这是一个错误还是我错过了一些东西？

Answer 1

正如您在报告导航器中的详细编译器消息中所看到的，您的方法未正确声明：

error: type 'ServerInfo' does not conform to protocol 'NSCoding'
class ServerInfo: NSObject, NSCoding {
^
Foundation.NSCoding:2:32: note: protocol requires function 'encodeWithCoder' with type '(NSCoder) -> Void'
  @objc(encodeWithCoder:) func encodeWithCoder(aCoder: NSCoder)
                               ^
note: candidate has non-matching type '(NSCoder!) -> ()'
    func encodeWithCoder(_aCoder: NSCoder!) {
         ^
Foundation.NSCoding:3:25: note: protocol requires initializer 'init(coder:)' with type '(coder: NSCoder)'
  @objc(initWithCoder:) init(coder aDecoder: NSCoder)
                        ^
note: candidate has non-matching type '(coder: NSCoder!)'
    init(coder aDecoder: NSCoder!) {

（这可能在beta版本之间发生了变化。）此外，必须将initWithCoder方法标记为required ：

required init(coder aDecoder: NSCoder) {   }

func encodeWithCoder(_aCoder: NSCoder) {   }

在Swift 3中 ，所需的方法是

required init(coder aDecoder: NSCoder) {   }

func encode(with aCoder: NSCoder) {   }

Answer 2

参数不是隐式解包（删除！），初始化程序需要required修饰符：

required init(coder aDecoder: NSCoder) {
...
func encodeWithCoder(_aCoder: NSCoder) {

对于Swift 3

已经提出了一个小但重要的变化。 init方法相同，但encodeWithCoder方法已被修改。

   required init(coder aDecoder: NSCoder) {
    ...
   }

   func encode(with _aCoder: NSCoder) { 
   ...
   }

Answer 3

对于Swift 3（在Xcode 8.2 beta（8C23）上）

它似乎又改变了。 这是我可以开始工作的唯一变种......

func encodeWithCoder(_ _aCoder: NSCoder) {
    ...
}