Swift:pickerView 的结果具有与协议(protocol) uipickerviewdelegate 预期的不同的可选性

Question

我收到关于可选性的警告:

Result of pickerView has different optionality than expected by protocol uipickerviewdelegate.

协议(protocol)似乎要我返回一个隐式展开的可选字符串，但我不确定该怎么做。

import UIKit

class TimerViewController: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate  {
  @IBOutlet var timerPickerView: UIPickerView!

  let timerPickerData = [Array(1...24), Array(1...60), Array(1...60)]

  ...

  func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String! {

    return String(timerPickerData[component][row])
  }

}

Answer 1

这是该委托(delegate)方法的 Swift 签名:

optional public func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String?

你可以在它的末尾看到它应该返回一个可选字符串 (String?)，而不是像这样的隐式展开的可选字符串 (String!)你有。所以警告的原因是因为协议(protocol)和您的实现之间的方法签名不同，特别是您将可选性从常规可选更改为隐式解包可选。