self.Gender.inputView =选择器线程1：致命错误：意外发现nil

Question

1. 导入UIKit     //主类

   class ViewController: UIViewController , UITextFieldDelegate , UIPickerViewDataSource , UIPickerViewDelegate {
       func numberOfComponents(in pickerView: UIPickerView) -> Int {
           return 1 ;
       }
   
       func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
           return self.genderType.count ;
       }
       func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
           return self.genderType[row];
       }
       func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
           self.Gender.text = self.genderType[row];
           self.Gender.endEditing(true)
       }
       //the IBOutlet
       @IBOutlet weak var Gender: UITextField!
   
       var genderType : [String] = ["Male" , "Female"];
       override func viewDidLoad() {
           super.viewDidLoad()
           let picker = UIPickerView()
           picker.delegate = self
           picker.dataSource = self
           **self.Gender.inputView = picker**
   
   
   
       }
   }