ios - Could not cast value of type exception in UIPickerView -

i implementing uipickerview populated parse.com objects. want show selected row string pickerview in textfield.

at execution, when user selects row textfield shows text when trying pass textfield text viewcontroller, app launches exception:

could not cast value of type

this code:

class citaservicio3: uiviewcontroller,uitextfielddelegate,uipickerviewdatasource,uipickerviewdelegate {     var receivednombre: string = ""     var receivedemail: string = ""     var receivedcelular: string = ""     var receivedtelefono: string = ""     var receivedfecha: string = ""     var receivedhora: string = ""      @iboutlet weak var vehiculopickerview: uipickerview!     @iboutlet var vehiculotextfield:uitextfield!      var pickerstring:nsmutablearray = []      override func viewdidload() {         super.viewdidload()          print("receivednombre=",receivednombre)         print("receivedemail=",receivedemail)         print("receivedcelular=",receivedcelular)         print("receivedtelefono=",receivedtelefono)         print("receivedfecha=",receivedfecha)         print("receivedhora=",receivedhora)          let query = pfquery(classname: "autos")         query.findobjectsinbackgroundwithblock({ (objects : [pfobject]?, error: nserror?) -> void in             if error == nil {                 object in objects! {                     print (object["modelo"])                     self.pickerstring.addobject(object["modelo"] as! string)                 }             }              self.vehiculopickerview.reloadallcomponents()         })     }      func numberofcomponentsinpickerview(pickerview: uipickerview) -> int     {         return 1     }      // returns # of rows in each component..     func pickerview(pickerview: uipickerview, numberofrowsincomponent component: int) -> int     {         return self.pickerstring.count     }       func pickerview(pickerview: uipickerview, titleforrow row: int, forcomponent component: int) -> string?     {         return self.pickerstring[row] as? string     }      func pickerview(pickerview: uipickerview, didselectrow row: int, incomponent component: int) {     self.vehiculotextfield.text  = self.pickerstring[row] as? string }      @ibaction func continuarbutton(sender: anyobject)      {         let vehiculocita = vehiculotextfield.text             if (vehiculocita!.isempty ){             let myalert = uialertcontroller(title: "faltan datos", message: "su vehiculo es obligatorio", preferredstyle: uialertcontrollerstyle.alert)             let okalert = uialertaction(title: "reintentar", style: uialertactionstyle.default, handler: nil)             myalert.addaction(okalert)             self.presentviewcontroller(myalert, animated: true, completion: nil)             return         }         [self .performseguewithidentifier("cita3a4", sender: self)]     }      override func prepareforsegue(segue: uistoryboardsegue, sender: anyobject!) {          print (segue.identifier)         print (vehiculotextfield.text)         if "cita3a4" == segue.identifier {             let cita4: citaservicio4 = segue.destinationviewcontroller as! citaservicio4              cita4.receivednombre = receivednombre             cita4.receivedemail = receivedemail             cita4.receivedcelular = receivedcelular             cita4.receivedtelefono = receivedtelefono             cita4.receivedfecha = receivedfecha             cita4.receivedvehiculo = vehiculotextfield.text!         }     } 

what wrong in code?

you saying:

let cita4: citaservicio4 = segue.destinationviewcontroller as! citaservicio4 

but destination view controller of segue not citaservicio4. (it is, in fact, citaservicio3.) therefore crash @ runtime when forced cast turns out impossible.

it seems structure of things in storyboard not think is. recheck segues, esp. storyboard identifiers , class of view controller lead.