swift - Cannot convert value of type 'String?' (Alamofire) -

i map class user object mapper:

class user: mappable{  private var _username: string! = nil private var _password: string! = nil private var _firstname: string! = nil private var _lastname: string! = nil  //here getters , setters(it takes space)  init(){  }  required init?(_ map: map) {  }  func mapping(map: map) {      username <- map["username"]     password <- map["password"]     firstname <- map["first_name"]     lastname <- map["last_name"]    } } 

and tried make new user , put values, map whole object , send alamofire this:

let useremail = useremailfield.text! let userpassword = userpasswordfield.text!  let user = user() user.username = useremail user.password = userpassword let jsonstring = mapper().tojsonstring(user, prettyprint: true)  alamofireservice.alamofireservice.makepostservicerequest(url_base, parameters: jsonstring, resposecallback: self) 

i followed instructions of libraries, error "cannot convert value of type 'string?' expected argument type '[string : anyobject]'", why?

alamofire request taking parameter in [string: anyobject] format need pass dictionary parameter. in case need like:

let useremail = useremailfield.text! let userpassword = userpasswordfield.text!  var dictparameter: dictionary<string, anyobject> = [:] dictparameter["username"]   = useremail dictparameter["password"]   = userpassword 

and after make request:

alamofireservice.alamofireservice.makepostservicerequest(url_base, parameters: dictparameter, resposecallback: self)