ios - 在我的方程求解程序中，输入 nil 值会使应用程序崩溃

Question

我制作了一个求解二次方程的应用程序(只是想看看我是否可以)，但是，如果用户不小心为其中一个槽输入任何值，我不希望该应用程序崩溃。请帮忙。

 @IBAction func solveButton(sender: AnyObject) {

        let a:Double! = Double(textFieldA.text!)      // textfieldA is UITextField
        let b:Double! = Double(textFieldB.text!)    // textfieldB is UITextField
        let c:Double! = Double(textFieldC.text!)   // textFieldC is UITextField

        // This is for if the a value is nil
        if a == nil && b == nil && c == nil{

            errorTextField.text = "Please do not leave an empty value, all quadratic equations must have 3 values!"
            answerLabel.text = " "

            answerLabelNegative.text = " "
            whatEquation.text = " "
            return

        } else {

            let a:Double! = Double(textFieldA.text!)      // textfieldA is UITextField
            let b:Double! = Double(textFieldB.text!)    // textfieldB is UITextField
            let c:Double! = Double(textFieldC.text!)   // textFieldC is UITextField
            let x:Double = (b * b)
            let y:Double = -4 * a * c //Here I get EXC_BAD_INSTRUCTION error
            let xy:Double = x + y
            let az:Double = sqrt(xy)
            let finalTopPlus:Double = -b + az
            let finalTopMinus:Double = -b - az
            let aTwo:Double = 2 * a
            let finalEquationPositive:Double = finalTopPlus / aTwo
            let finalEquationNegative:Double = finalTopMinus / aTwo

            answerLabel.text = "Positive x = \(finalEquationPositive)"
            answerLabelNegative.text = "Negative x = \(finalEquationNegative)"

            let aValue = a < 0 ? "-" : " "
            let bValue = b < 0 ? " " : "+"
            let cValue = c < 0 ? " " : "+"
            whatEquation.text = "Equation: \(aValue) \(a)x² \(bValue) \(b)x \(cValue) \(c)"
        }

Answer 1

您的 if 语句检查是否所有值都为 nil。您想查看其中是否有nil。

将if更改为:

if a == nil || b == nil || c == nil {

我不会使用 Swift 进行编程，但我的印象是，您应该进行许多其他改进来验证值不是 nil。