错误：PickerView无法将类型'[String]'的返回表达式转换为类型'String？' ”

Question

在Xcode Swift中使用PickerView在此代码中出现错误：

func pickerView(pikcerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String! {
    return pickerDate [row] // Cannot convert return expression of type '[String]' to return type 'String?'

        }

PickerView的完整代码：

@IBOutlet weak var inputpickerdate: UIPickerView!

   // var pickerList = ["test","test2","test3"]

    var pickerDate: [[String]] = [[String]] ()
        //[pickerModel] ()

    var selected: String?

    override func viewDidLoad() {
        super.viewDidLoad()

    self.inputpickerdate.delegate = self
    self.inputpickerdate.dataSource = self

        pickerDate = [["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"], ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31"], ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sept", "Oct", "Nov", "Dec"]]


 func numberOfComponents(in pickerView: UIPickerView) -> Int {

        return 3
    }


func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {

    return pickerDate.count
        }
func pickerView(pikcerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String! {
    return pickerDate [row]

        }

我正在尝试创建一个带有星期几，日期和月份的PickerView，例如3月2日星期一

但是，我已经这样做并获得了

  

错误：无法将类型为[[String]'的返回表达式转换为返回值   输入“字符串？”

在我的func titleForRow中，不确定我为什么得到这个。

Answer 1

您有一个列表列表。

[]->列表。

[[]]->列表列表。

您将返回列表[]而不是String?。 在您的情况下，您必须使用类似以下的内容：

func pickerView(pikcerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
    return pickerDate[component][row] // if component starts with 0.
}

当然，您必须做出逻辑以获取正确的字段。

Answer 2

首先，您使用了错误的titleForRow委托方法。应该是：

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

接下来，您需要替换

return pickerDate [row]

与

return pickerDate[component][row]

您的方法将是：

func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
    return pickerDate[component][row]
}

您的选择器将如下所示：

Answer 3

您将返回Array = return pickerDate [row]的字符串，该字符串应为单个字符串。