ios - UIPickerView:在展开可选值时意外发现 nil

Question

我正在尝试为我的应用程序实现一个 UIPickerView。虽然我没有遇到错误，但当我运行该应用程序时它崩溃并出现以下错误:

unexpectedly found nil while unwrapping an Optional value

class LobbyViewController: UIViewController {


   @IBOutlet weak var textfield: UITextField!
   var picker: UIPickerView!

   var radius = [2, 5, 10, 15, 20, 25, 50, 100, 1000]


   override func viewDidLoad() {
        super.viewDidLoad()
        picker.dataSource = self
        picker.delegate = self
        self.textfield.inputView = picker
   }

   override func didReceiveMemoryWarning() {
       super.didReceiveMemoryWarning()
   }

}

extension LobbyViewController: UIPickerViewDataSource {

   func numberOfComponentsInPickerView(picker: UIPickerView!) -> Int
   {
       return 1
   }

   func pickerView(picker: UIPickerView!, numberOfRowsInComponent component: Int) -> Int{
       return radius.count
   }

}

extension LobbyViewController: UIPickerViewDelegate{
    func pickerView(umkreisPicker: UIPickerView!, titleForRow row: Int, forComponent component: Int) -> String {
        return radius[row]
    }

}

希望你能帮助我!

Answer 1

你永远不会创建你的 UIPickerView 实例 - picker 应该被标记为 @IBOutlet 并连接到你的 Storyboard中或者您应该在设置委托(delegate)和数据源之前创建它。