ios – Swift：不符合协议NSCoding

我正在尝试在 swift中使用NSCoding协议,但是似乎无法弄清楚为什么编译器会抱怨当我实现所需的方法时它“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bug还是我只是想念一些东西？

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!) {

required init(coder aDecoder: NSCoder) {   }

func encodeWithCoder(_aCoder: NSCoder) {   }

required init(coder aDecoder: NSCoder) {   }

func encode(with aCoder: NSCoder) {   }