Question

我正在解决正确计算的问题（这太棒了）但是如果我在模拟器中留下一个空白的文本字段就会崩溃（不是真棒）或者：当编码方式不同时，空白文本字段没有崩溃（不好）但计算不正确（不好）。

这是我正在尝试做的事情：获取4个值的用户输入：计数纤维，计算空白纤维（如果它为零则确定），计算的字段和样品体积。我提出了默认值，希望能够处理文本框为空白的任何实例，希望能够防止崩溃。然后应用程序计算纤维密度，检测限和样品结果。现在非常简单，但我希望稍后加入。

我的主要问题是选项。我已经阅读过并尽力准确地编写代码，但有时候Xcode迫使我进入角落。所以我的应用程序在文本字段为空时崩溃。或者我可以防止崩溃，但不知何故，默认值将在计算中使用，实际数据将关闭。

我必须错误地使用if-let，所以我尝试了你在下面的代码中看到的内容。

我会把代码放在下面，并且一如既往地感谢任何帮助，并理解我是新手并且在自学成才的同时试图理解这些概念（除了这里学到的经验教训）。谢谢！

import UIKit

类ViewController：UIViewController {

@IBOutlet weak var fibersCountedTextField: UITextField!

@IBOutlet weak var blankFibersCountedTextField: UITextField!

@IBOutlet weak var fieldsCountedTextField: UITextField!

@IBOutlet weak var sampleVolumeTextField: UITextField!

@IBOutlet weak var fiberDensityLabel: UILabel!

@IBOutlet weak var limitOfDetectionLabel: UILabel!

@IBOutlet weak var sampleResultLabel: UILabel!

@IBAction func calculateBtnPressed(_ sender: Any) {

    var blankCheck: String?
    var blankFibersCounted: Double?
    var fibersCheck: String?
    var fibersCounted: Double?
    var fieldsCheck: String?
    var fieldsCounted: Double?
    var volumeCheck: String?
    var sampleVolume: Double?
    var sampleResultNumerator: Double?
    var sampleResultDenominator: Double?
    var sampleResult: Double?
    var sampleResultRounded: Double
    var fiberDensity: Double
    var fiberDensityRounded: Double
    var limitOfDetectionNumerator: Double
    var limitOfDetectionDenominator: Double
    var sampleLimitOfDetection: Double
    var sampleLimitOfDetectionRounded: Double

    struct TypicalSampleData {
        let typicalBlankFibersCounted: Double
        let typicalFibersCounted: Double
        let typicalFieldsCounted: Double
        let typicalSampleVolume: Double

        init(typicalBlankFibersCounted: Double = 4.0, typicalFibersCounted: Double = 5.5, typicalFieldsCounted: Double = 100.0, typicalSampleVolume: Double = 555.0) {
            self.typicalBlankFibersCounted = typicalBlankFibersCounted
            self.typicalFibersCounted = typicalFibersCounted
            self.typicalFieldsCounted = typicalFieldsCounted
            self.typicalSampleVolume = typicalSampleVolume
        }
    }

    //this code calculates correctly but crashes if text boxes left empty in the simulator.

    let defaultSampleData = TypicalSampleData()

    //if let blankCheck = blankFibersCountedTextField.text {
      //  blankFibersCounted = Double(blankCheck)
    //} else {
      // blankFibersCounted = defaultSampleData.typicalBlankFibersCounted
    //}

    //blankCheck = blankFibersCountedTextField.text

    //var blankCheckDbl: Double?

    //if let blankCheck = blankFibersCountedTextField.text {
      //  blankFibersCounted = Double(blankCheck)
    //}; blankFibersCounted = defaultSampleData.typicalBlankFibersCounted

    //if let fibersCheck = fibersCountedTextField.text {
      //  fibersCounted = Double(fibersCheck)
    //} else {
      //  fibersCounted = defaultSampleData.typicalFibersCounted
    //}

    if blankFibersCountedTextField != nil {
        blankCheck = blankFibersCountedTextField.text
    } else {
        blankFibersCounted = defaultSampleData.typicalBlankFibersCounted
    }

    if blankCheck == blankFibersCountedTextField.text {
        blankFibersCounted = Double(blankCheck!)
    } else {
        blankFibersCounted = defaultSampleData.typicalBlankFibersCounted
    }

    if fibersCountedTextField != nil {
        fibersCheck = fibersCountedTextField.text
    } else {
        fibersCounted = defaultSampleData.typicalFibersCounted
    }

    if fibersCheck == fibersCountedTextField.text {
        fibersCounted = Double(fibersCheck!)
    } else {
        fibersCounted = defaultSampleData.typicalFibersCounted
    }

    if fieldsCountedTextField != nil {
        fieldsCheck = fieldsCountedTextField.text
    } else {
        fieldsCounted = defaultSampleData.typicalFieldsCounted
    }

    if fieldsCheck == fieldsCountedTextField.text {
        fieldsCounted = Double(fieldsCheck!)
    } else {
        fieldsCounted = defaultSampleData.typicalFieldsCounted
    }

    if sampleVolumeTextField != nil {
        volumeCheck = sampleVolumeTextField.text
    } else {
        sampleVolume = defaultSampleData.typicalSampleVolume
    }

    if volumeCheck == sampleVolumeTextField.text {
        sampleVolume = Double(volumeCheck!)
    } else {
        sampleVolume = defaultSampleData.typicalSampleVolume
    }

    //if let fibersCheck = fibersCountedTextField.text {
      //  fibersCounted = Double(fibersCheck)
    //}; fibersCounted = defaultSampleData.typicalFibersCounted

    //if let fieldsCheck = fieldsCountedTextField.text {
      //  fieldsCounted = Double(fieldsCheck)
    //} else {
      //   fieldsCounted = defaultSampleData.typicalFieldsCounted
    //}

    //if let fieldsCheck = fieldsCountedTextField.text {
      //  fieldsCounted = Double(fieldsCheck)
    //}; fieldsCounted = defaultSampleData.typicalFieldsCounted

    //if let volumeCheck = sampleVolumeTextField.text {
      //  sampleVolume = Double(volumeCheck)
    //} else {
      // sampleVolume = defaultSampleData.typicalSampleVolume
    //}

    //if let volumeCheck = sampleVolumeTextField.text {
      //  sampleVolume = Double(volumeCheck)
    //}; sampleVolume = defaultSampleData.typicalSampleVolume

    //calculate result
    if let fibersCounted = fibersCounted, fibersCounted < 5.5 {
        sampleResultNumerator = (385 * (5.5 / 100))
        sampleResultDenominator = (7.85 * sampleVolume!)
        sampleResult = sampleResultNumerator! / sampleResultDenominator!
    } else {
        sampleResultNumerator = 385 * ((fibersCounted! - blankFibersCounted!) / fieldsCounted!)
        sampleResultDenominator = (7.85 * sampleVolume!)
        sampleResult = sampleResultNumerator! / sampleResultDenominator!
    }

    sampleResultRounded = Double(round(1000 * sampleResult!)/1000)

    //calculate sample limit of detection
    //insert if-let statement here, similar to above?
    limitOfDetectionNumerator = 385 * (5.5 / 100)
    limitOfDetectionDenominator = (7.85 * sampleVolume!)
    sampleLimitOfDetection = limitOfDetectionNumerator / limitOfDetectionDenominator
    sampleLimitOfDetectionRounded = Double(round(1000 * sampleLimitOfDetection)/1000)

    //calculate fiber density
    //insert if-let statement here, similar to above?
    fiberDensity = ((fibersCounted! - blankFibersCounted!) / fieldsCounted!) / 0.00785
    fiberDensityRounded = Double(round(1000 * fiberDensity)/1000)

    fiberDensityLabel.text = String(fiberDensityRounded)
    limitOfDetectionLabel.text = String(sampleLimitOfDetectionRounded)
    sampleResultLabel.text = String(sampleResultRounded)

}

override func viewDidLoad() {
  super.viewDidLoad()

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()

}

}

Answer 1

有多种方法可以处理您的任务，但这是一个非常直接的方法（用您的实际@IBOutlet名称替换fieldA，fieldB等）：

@IBAction func calculateBtnPressed(_ sender: Any) {

    let defaultSampleData = TypicalSampleData()

    // get the text from fieldA - set it to "" if fieldA.text is nil
    let textA = fieldA.text ?? ""

    // get the text from fieldB - set it to "" if fieldB.text is nil
    let textB = fieldB.text ?? ""

    // if textA CAN be converted to a Double, use it, otherwise use default value
    let valA = Double(textA) ?? defaultSampleData.typicalBlankFibersCounted

    // if textB CAN be converted to a Double, use it, otherwise use default value
    let valB = Double(textB) ?? defaultSampleData.typicalFibersCounted

    // set resultLabel.text to the product of valA and valB
    resultLabel.text = "Result: \(valA * valB)"

}

这个想法是：确保你的“等式”的每个部分都有默认值。

当然，根据您的实际用例，您可能希望显示错误弹出消息而不是使用默认值。但这应该让你顺利。

卡住正确计算，或使用崩溃的代码

1 个答案: