ios - Swift 中的选择器 View

Question

我在 didSelectRow 函数的选取器 View 中遇到应用程序问题

在某些情况下，选择器 View 可能为零，因此 didSelectRow 内的所有指令都将读取无值，并且应用程序崩溃。

我多次尝试使用不同的解决方案来防止此崩溃，但它不起作用:

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int)  {
        if (self.MEDARRAY[row].value(forKey: "medNumDay") as? NSInteger) != nil {

        let NumDay = self.MEDARRAY[row].value(forKey: "medNumDay") as? NSInteger
        let NumMed = self.MEDARRAY[row].value(forKey: "medNum") as? NSInteger
        Counter = (self.MEDARRAY[row].value(forKey: "takenCounter") as? NSInteger)!
        theTimeSet = (self.MEDARRAY[row].value(forKey: "nextTime")as? Date)!
        numberforday = (24 / NumDay!)
        thegetting.timeStyle = DateFormatter.Style.short
        TotalDose.text = String(NumDay! * NumMed!)
        RemainDose.text = String(Int(TotalDose.text!)! - Counter!)
        NextTimes.text = thegetting.string(from: theTimeSet!)
        }
        else{
                TotalDose.text = "No"
                RemainDose.text = "No"
                NextTimes.text = "No"            
        }
}

再次尝试

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int)  {
        if (MEDARRAY.count < 1) {
    let NumDay = self.MEDARRAY[row].value(forKey: "medNumDay") as? NSInteger
    let NumMed = self.MEDARRAY[row].value(forKey: "medNum") as? NSInteger
    Counter = (self.MEDARRAY[row].value(forKey: "takenCounter") as? NSInteger)!
    theTimeSet = (self.MEDARRAY[row].value(forKey: "nextTime")as? Date)!
    numberforday = (24 / NumDay!)
    thegetting.timeStyle = DateFormatter.Style.short
    TotalDose.text = String(NumDay! * NumMed!)
    RemainDose.text = String(Int(TotalDose.text!)! - Counter!)
    NextTimes.text = thegetting.string(from: theTimeSet!)
    }
    else{
            TotalDose.text = "No"
            RemainDose.text = "No"
            NextTimes.text = "No"            
    }
}

问题是它仍然试图通过此错误:索引超出范围来获取以下代码的值

let NumDay = self.MEDARRAY[row].value(forKey: "medNumDay") as? NSInteger
let NumMed = self.MEDARRAY[row].value(forKey: "medNum") as? NSInteger
Counter = (self.MEDARRAY[row].value(forKey: "takenCounter") as? NSInteger)!
theTimeSet = (self.MEDARRAY[row].value(forKey: "nextTime")as? Date)!

Answer 1

如果您要识别的项目是可选的，但您需要它们具有非零值来执行函数，请在函数的头部放置一个保护语句来测试每个值是否可用:

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
    guard row < MEDARRAY.count,
          MEDARRAY.count < 1,
          let NumDay : NSInteger = self.MEDARRAY[row].value(forKey: "medNumDay") as NSInteger,
          let NumMed = self.MEDARRAY[row].value(forKey: "medNum") as NSInteger,
          let Counter = (self.MEDARRAY[row].value(forKey: "takenCounter") as NSInteger
          let theTimeSet = (self.MEDARRAY[row].value(forKey: "nextTime") as Date else { print("Could not obtain all required values") ; return }

     // ... function continues here...

请注意，您可以用逗号链接保护语句，并且这些常量不是可选的:如果非零值可用，它们将被初始化为非可选，否则将触发保护异常。 (另请注意对数组测试和行输入的更正。)

这样，如果您无法将这些常量初始化为非零值，该函数将直接退出，这应该可以防止应用程序崩溃。当然，这并不能解决为什么值为零的问题，但至少可以让执行继续进行。

希望有帮助。