在UILabel上显示数学字符串

Question

我想显示计算器中输入的一串计算结果。就像2+4*3/4-6 当用户水龙头2应该更新标签和写的UILabel 2，然后写操作+等等...

我上传整个代码，因为它很复杂在这里解释每个函数：

import UIKit 

// Basic math functions 
func add(_ a: Double, b: Double) -> Double { 
    let result = a + b 
    return result 
} 
func sub(_ a: Double, b: Double) -> Double { 
    let result = a - b 
    return result 
} 
func mul(_ a: Double, b: Double) -> Double { 
    let result = a * b 
    return result 
} 
func div(_ a: Double, b: Double) -> Double { 
    let result = a/b 
    return result 
} 

typealias Binop = (Double, Double) -> Double 
let ops: [String: Binop] = [ "+" : add, "-" : sub, "*" : mul, "/" : div ] 


class Calculator: UIViewController { 

    var accumulator: Double = 0.0 // Store the calculated value here 


    var userInput = "" // User-entered digits 

    var numStack: [Double] = [] // Number stack 
    var opStack: [String] = [] // Operator stack 



    // Looks for a single character in a string. 
    func hasIndex(stringToSearch str: String, characterToFind chr: Character) -> Bool { 
     for c in str.characters { 
      if c == chr { 
       return true 
      } 
     } 
     return false 
    } 

    func handleInput(_ str: String) { 
     if str == "-" { 
      if userInput.hasPrefix(str) { 
       // Strip off the first character (a dash) 
       userInput = userInput.substring(from: userInput.characters.index(after: userInput.startIndex)) 
      } else { 
       userInput = str + userInput 
      } 
     } else { 
      userInput += str 
     } 
     accumulator = Double((userInput as NSString).doubleValue) 
     updateDisplay() 
    } 

    func updateDisplay() { 
     // If the value is an integer, don't show a decimal point 
     let iAcc = Int(accumulator) 
     if accumulator - Double(iAcc) == 0 { 
      numField.text = "\(iAcc)" 
     } else { 
      numField.text = "\(accumulator)" 
     } 
    } 

    func doMath(_ newOp: String) { 
     if userInput != "" && !numStack.isEmpty { 
      let stackOp = opStack.last 
      if !((stackOp == "+" || stackOp == "-") && (newOp == "*" || newOp == "/")) { 
       let oper = ops[opStack.removeLast()] 
       accumulator = oper!(numStack.removeLast(), accumulator) 
       doEquals() 
      } 
     } 
     opStack.append(newOp) 
     numStack.append(accumulator) 
     userInput = "" 
     updateDisplay() 
    } 

    func doEquals() { 
     if numField.text == "8520" 
     { 
      performSegue(withIdentifier: "VaultSegue", sender: self) 
      numField.text = "" 
     } 

     else if userInput == "" { 
      return 
     } 
     if !numStack.isEmpty { 
      let oper = ops[opStack.removeLast()] 
      accumulator = oper!(numStack.removeLast(), accumulator) 
      if !opStack.isEmpty { 
       doEquals() 
      } 
     } 
     updateDisplay() 
     userInput = "" 
    } 

    // UI Set-up 

    //@IBOutlet var numField: UITextField! 

    @IBOutlet weak var numField: UILabel! 
    @IBOutlet var btnClear: UIButton! 
    @IBOutlet var bntEquals: UIButton! 
    @IBOutlet var btnAdd: UIButton! 
    @IBOutlet var btnSubtract: UIButton! 
    @IBOutlet var btnMultiply: UIButton! 
    @IBOutlet var btnDivide: UIButton! 
    @IBOutlet var btnDecimal: UIButton! 

    @IBOutlet var btn0: UIButton! 
    @IBOutlet var btn1: UIButton! 
    @IBOutlet var btn2: UIButton! 
    @IBOutlet var btn3: UIButton! 
    @IBOutlet var btn4: UIButton! 
    @IBOutlet var btn5: UIButton! 
    @IBOutlet var btn6: UIButton! 
    @IBOutlet var btn7: UIButton! 
    @IBOutlet var btn8: UIButton! 
    @IBOutlet var btn9: UIButton! 

    @IBAction func btn0Press(_ sender: UIButton) { 
     handleInput("0") 
    } 
    @IBAction func btn1Press(_ sender: UIButton) { 
     handleInput("1") 
    } 
    @IBAction func btn2Press(_ sender: UIButton) { 
     handleInput("2") 
    } 
    @IBAction func btn3Press(_ sender: UIButton) { 
     handleInput("3") 
    } 
    @IBAction func btn4Press(_ sender: UIButton) { 
     handleInput("4") 
    } 
    @IBAction func btn5Press(_ sender: UIButton) { 
     handleInput("5") 
    } 
    @IBAction func btn6Press(_ sender: UIButton) { 
     handleInput("6") 
    } 
    @IBAction func btn7Press(_ sender: UIButton) { 
     handleInput("7") 
    } 
    @IBAction func btn8Press(_ sender: UIButton) { 
     handleInput("8") 
    } 
    @IBAction func btn9Press(_ sender: UIButton) { 
     handleInput("9") 
    } 

    @IBAction func btnDecPress(_ sender: UIButton) { 
     if hasIndex(stringToSearch: userInput, characterToFind: ".") == false { 
      handleInput(".") 
     } 
    } 

    @IBAction func btnCHSPress(_ sender: UIButton) { //change sign 
     if userInput.isEmpty { 
      userInput = numField.text! 
     } 
     handleInput("-") 
    } 

    @IBAction func btnACPress(_ sender: UIButton) { //all clear 
     userInput = "" 
     accumulator = 0 
     updateDisplay() 
     numStack.removeAll() 
     opStack.removeAll() 
    } 

    @IBAction func btnPlusPress(_ sender: UIButton) { 
     doMath("+") 
    } 

    @IBAction func btnMinusPress(_ sender: UIButton) { 
     doMath("-") 
    } 

    @IBAction func btnMultiplyPress(_ sender: UIButton) { 
     doMath("*") 
    } 

    @IBAction func btnDividePress(_ sender: UIButton) { 
     doMath("/") 
    } 

    @IBAction func btnEqualsPress(_ sender: UIButton) { 
     doEquals() 
    } 
} 

Answer 1

每次更新标签文本时都会新建函数和调用。

代码功能如下：

func updateLabel(_ newText: String) { 
     lblString.text! += newText 
    } 

这里lblString是标签。