為什么我的if函式不能阻止轉到下一個視圖控制器？-有解無憂

我有一系列 if 函式來檢查兩個文本欄位是否為空（或只是其中一個），如果是，則在標簽中顯示錯誤訊息。如果兩個文本欄位都不是空的，那么它應該執行計算，然后轉到下面的視圖控制器并在標簽中顯示方程的值。然而，即使有 if 函式檢查文本欄位是否為 nil，segue 仍然會被執行，即使它們是 nil，錯誤標簽也是如此。為什么 if 函式不能阻止這種情況？

@IBAction func CalcFlowRateEnd(_ sender: UIButton) {
  
    let volume = Double(VolTextField.text!)
    let time = Double(SecTextField.text!)
    let units = volumeUnitsPicker4.selectedRow(inComponent: 0)
    var selectedUnit = data[units]

        
        //milliliters error labels
    if selectedUnit == "milliliters" && volume == nil && time == nil {
            volErrorLabel.text = "Enter Volume"
            secErrorLabel.text = "Enter Seconds"}
        
    if selectedUnit == "milliliters" && volume != nil && time == nil {
            secErrorLabel.text = "Enter Seconds"}
        
    if selectedUnit == "milliliters" && volume == nil && time != nil {
            volErrorLabel.text = "Enter Volume"}
        
        
        //milliliters calc
    if selectedUnit == "milliliters" && volume != nil && time != nil{
    
    let volumeConvert = Double(volume!/1000)
    let timeConvert = Double(time! / 60)
    let flowRateMetric = Double(volumeConvert / timeConvert)
    let volumeImperial = Double(volume!/4546)
    let flowRateImperial = Double(volumeImperial / timeConvert)
    let roundedMetric = round(flowRateMetric * 100) / 100.0
    let roundedImperial = round(flowRateImperial * 100) / 100.0
            
    calcFlowRate.text = "\(roundedMetric) liters per min or \(roundedImperial) gal per min"
        
    func prepare(for segue: UIStoryboardSegue, sender: Any?) {
                 
    let flowRate = calcFlowRate.text ?? ""
    let destinationVC = segue.destination as! FlowRateCalcEndViewController
    destinationVC.flowRate = flowRate
            
    }

uj5u.com熱心網友回復：

該prepare(for segue)函式不應嵌套在您的@IBAction函式中。

func prepare(for segue)應該被覆寫。在執行 segue 之前呼叫它，因此您有機會“做某事”

var isFlowRateCalculated = false

@IBAction func CalcFlowRateEnd(_ sender: UIButton) {
    if selectedUnit == "milliliters" && volume != nil && time != nil {
    // logic

    isFlowRateCalculated = true
   }
}

override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
    return isFlowRateCalculated
}

override func prepare(for segue) {
    // hand off data for view being presented
}

這并不能解決您的全部問題，但這是朝著正確方向邁出的一步。很高興繼續和你談論這個:)

我還建議在Medium上查看這篇文章

轉載請註明出處，本文鏈接：https://www.uj5u.com/ruanti/419175.html

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