ios - Passing a Double between ViewControllers Swift 3 -

total noob here swift 3. need pass double value 1 viewcontroller via 2 user input text fields. i've tried numerous solutions , have read can find on passing data between viewcontrollers. 'fatal error: unexpectedly found nil while unwrapping optional value'. have real hard time understand wrapping , unwrapping of variables , i'm sure it's simple.

here first viewcontroller:

import uikit  var longitude: double? var latitude: double?    class viewcontroller: uiviewcontroller {  @iboutlet var getlongitude: uitextfield! @iboutlet var getlatitude: uitextfield!  @iboutlet var mapbutton: uibutton!  override func viewdidload() {     super.viewdidload()          }  override func didreceivememorywarning() {     super.didreceivememorywarning()     // dispose of resources can recreated. }  @ibaction func mapbtn(_ sender: any) {      performsegue(withidentifier: "segue", sender: self)     longitude = double(getlongitude.text!)!     latitude = double(getlatitude.text!)!  }  } 

and secondviewcontroller:

class secondviewcontroller: uiviewcontroller {  override func viewdidload() {     super.viewdidload()      let camera = gmscameraposition.camera(withlatitude: latitude!, longitude: longitude!, zoom: 6.0)     let mapview = gmsmapview.map(withframe: cgrect.zero, camera: camera)     view = mapview     // creates marker in center of map.     let marker = gmsmarker()     marker.position = cllocationcoordinate2d(latitude: latitude!, longitude: longitude!)     marker.map = mapview  }  override func didreceivememorywarning() {     super.didreceivememorywarning()     // dispose of resources can recreated. } 

}

avoid global mutable state. send data 1 scene another.

try this:

class viewcontroller: uiviewcontroller {    @iboutlet weak var longitudetextfield: uitextfield!   @iboutlet weak var latitudetextfield: uitextfield!   @iboutlet weak var mapbutton: uibutton!    @ibaction func didtaptomapbutton(_ sender: uibutton) {      // assume storyboard' name main. if not, change below accordingly     let mainstoryboard = uistoryboard(name: "main", bundle: nil)      // assume destination view controller' identifier , type secondviewcontroller. if not, change below accordingly.     if let secondviewcontroller = mainstoryboard.instantiateviewcontroller(withidentifier: "secondviewcontroller") as? secondviewcontroller {        if let longitude = double(longitudetextfield.text),         let latitude = double(latitudetextfield.text) {          secondviewcontroller.latitude = latitude         secondviewcontroller.longitude = longitude       }        present(secondviewcontroller, animated: true, completion: nil)     }   } }  class secondviewcontroller: uiviewcontroller {    var latitude: double?   var longitude: double?    override func viewdidload() {     super.viewdidload()      if let latitude = latitude,       let longitude = longitude {        let camera = gmscameraposition.camera(withlatitude: latitude, longitude: longitude, zoom: 6.0)       let mapview = gmsmapview.map(withframe: cgrect.zero, camera: camera)       view = mapview        // creates marker in center of map.       let marker = gmsmarker()       marker.position = cllocationcoordinate2d(latitude: latitude, longitude: longitude)       marker.map = mapview     }   } }