ios - Swift 计算器运算符问题

Question

大家好，感谢您访问我的页面。我目前正在学习为我的类(class)创建一个计算器，但注意到在我输入时出现错误，例如:

5 + 5 = 10//这是正确的

5 + 2 * 3 + 5 = 26//还没有问题

5 + 2 = 7 +(将添加最后一个带有数字的运算符。这意味着在我选择要添加的数字之前屏幕将显示 9。)

任何关于我应该如何思考以解决这个问题的建议将不胜感激。

import UIKit
import AVFoundation

class ViewController: UIViewController {

    enum Operation: String {
        case Divide = "/"
        case Multiple = "*"
        case Subtract = "-"
        case Add = "+"
        case Empty = "Empty"
    }

    @IBOutlet weak var outputLbl: UILabel!

    // This is initialized once the app loads. 

    var btnSound: AVAudioPlayer!

    var runningNumber = ""
    var leftValStr = ""
    var rightValStr = ""
    var currentOperation: Operation = Operation.Empty
    var result = ""


    override func viewDidLoad() {
        super.viewDidLoad()

        let path = NSBundle.mainBundle().pathForResource("btn", ofType: "wav")
        let soundUrl = NSURL(fileURLWithPath: path!)

        do {
            try btnSound = AVAudioPlayer(contentsOfURL: soundUrl)
            btnSound.prepareToPlay()
        } catch let err as NSError {
            print(err.debugDescription)
        }
        // Do any additional setup after loading the view, typically from a nib.
    }

    @IBAction func numberPressed(btn: UIButton) {
        playSound()

        // Each button is assigned to a tag from 0-9. 
        // When button is pressed it is stored to btn.
        runningNumber += "\(btn.tag)"
        outputLbl.text = runningNumber
    }

    @IBAction func onDividePressed(sender: AnyObject) {
        processOperation(Operation.Divide)
    }

    @IBAction func onMultiplyPressed(sender: AnyObject) {
        processOperation(Operation.Multiple)
    }

    @IBAction func onSubtractPressed(sender: AnyObject) {
        processOperation(Operation.Subtract)
    }

    @IBAction func onAddPressed(sender: AnyObject) {
        processOperation(Operation.Add)
    }

    @IBAction func onEqualPressed(sender: AnyObject) {
        processOperation(currentOperation)
    }

    @IBAction func onClearPressed(sender: AnyObject) {
        clearCalcuator()
    }



    // op is what is storing the Operator. It could have been named anything
    func processOperation(op: Operation) {
        playSound()

        if currentOperation != Operation.Empty {
            // Run some math.

            // A user selected an operator, but then selected another
            // operator without first selecting a number
            if runningNumber != "" {
                rightValStr = runningNumber
                runningNumber = ""

            }

            if currentOperation == Operation.Multiple {
                result = "\(Double(leftValStr)! * Double(rightValStr)!)"
            } else if currentOperation == Operation.Divide {
                result = "\(Double(leftValStr)! / Double(rightValStr)!)"
            } else if currentOperation == Operation.Subtract {
                result = "\(Double(leftValStr)! - Double(rightValStr)!)"
            } else if currentOperation == Operation.Add {
                result = "\(Double(leftValStr)! + Double(rightValStr)!)"
            }

            leftValStr = result
            outputLbl.text = result

            currentOperation = op

        } else {
            // This is the first time an Operator has been pressed.

            leftValStr = runningNumber
            runningNumber = ""
            currentOperation = op
        }
    }

    func clearCalcuator() {
        playSound()

        if outputLbl.text != "0" {
            runningNumber = ""
            leftValStr = ""
            rightValStr = ""
            currentOperation = Operation.Empty

        }

        outputLbl.text = "0"
    }


    // Function was created to keep the code DRY. 
    // Now can use playSound() on top. Exp: Line 51
    func playSound() {
        if btnSound.playing {
            btnSound.stop()
        }

        btnSound.play()
    }
}

我仍然是 SWIFT 的初学者，但希望通过向更了解 SWIFT 的人学习来提高水平。如果您对我当前的代码有任何关于如何改进的建议，欢迎所有建议。再次感谢你。

Answer 1

您描述的行为是 = 的 @IBAction 正在传递 currentOperation< 的 Operation 的结果，这意味着如果最后一个操作是 +，则意味着 = 按钮的行为就像再次点击 + .这就是为什么您会看到自己的行为。

为了解决这个问题，您需要确保当您按下 = 时，processOperation 会将 currentOperation 设置为其他内容，以便当您下一次调用 processOperation，不再执行进一步的计算。为此，您需要做的就是为 = 添加一个 case 到 Operation:

enum Operation: String {
    case Divide = "/"
    case Multiple = "*"
    case Subtract = "-"
    case Add = "+"
    case Equal = "="
    case Empty = "Empty"
}

然后将 = 的 @IBAction 更改为仅传递此 Operation 而不是 currentOperation:

@IBAction func onEqualPressed(sender: AnyObject) {
    processOperation(.Equal)
}

因此，当您调用 processOperation 时，这将执行 currentOperation，然后当它完成时，它将 currentOperation 重置为 Operation.Equal，下一次调用 processOperation 时，它不会重复任何基于 .Equal 的进一步计算。