如何为一个简单的计算器应用程序集成 NumberFormatter？

有很多方法可以解决这个问题 -- 你可能想搜索现有的例子。

不过有一些建议......

看起来您在值和字符串之间转换，并过多地评估字符串。

最好保持值，并且仅在需要显示时才设置它们的格式。

因此，首先，我们可以沿着这些思路思考。

假设我们已经检查了按钮并将其转换为...var curVal: Double.currentTitlebtnVal: Double

    curVal = 0
    
    // user taps "5"
    curVal *= 10.0
    curVal += btnVal
    // curVal now equals 5
    
    // user taps "3"
    curVal *= 10.0
    curVal += btnVal
    // curVal now equals 53

    // user taps "7"
    curVal *= 10.0
    curVal += btnVal
    // curVal now equals 537
    

因此，每次我们更改 的值时，我们都会使用更新“显示”标签。curValNumberFormatter

如果我们输入一个负数，我们需要做一些不同的操作。为此，我们将减去 if is less-than-Zero：curValbtnValcurVal

    // user taps "5"
    curVal *= 10.0
    curVal += curVal >= 0 ? btnVal : -btnVal
    // curVal now equals 5
    
    // user taps "+/-"
    curVal *= -1.0
    // curVal now equals -5
    
    // user taps "3"
    curVal *= 10.0
    curVal += curVal >= 0 ? btnVal : -btnVal
    // curVal now equals -53
    
    // user taps "7"
    curVal *= 10.0
    curVal += curVal >= 0 ? btnVal : -btnVal
    // curVal now equals -537
    
    // user taps "+/-" again
    curVal *= -1.0
    // curVal now equals 537
    

NumberFormatter将在需要时自动添加“-”...因此，无需再看字符串是否以“-”开头或需要插入“-”。

当然，如果我们尝试在小数点后输入数字，这将不起作用！

因此，我们需要跟踪“十进制计数”并将其除以 10、100、1000 等，然后再将其添加到 .btnValcurVal

让我们看看我们的按钮点击处理程序可能开始是什么样子的：

@objc func btnTapped(_ sender: UIButton) {
    
    guard let title = sender.currentTitle else { return }
    
    // if it's a number button
    if let val = Double(title) {
        var p: Double = 0
        var btnVal: Double = val

        // if "decimal count" is greater-than-Zero,
        //  we need to divide the input value by 10, 100, 1000, etc
        if decCount > 0 {
            p = pow(10.0, Double(decCount))
            btnVal /= p
            decCount += 1
        } else {
            currentValue *= 10.0
        }
        currentValue += currentValue >= 0 ? btnVal : -btnVal

        // if we have decimal values, we need to round the result
        //  due to floating-point precision
        //  e.g. if we enter "0" "." "1" "2"
        //  the actual value is 0.12000000000000002048
        //  so we round to the current number of decimal places
        if p > 0 {
            currentValue = round(currentValue * p) / p
        }
    }

    // if decimal button tapped
    if title == decimalSym {
        if decCount == 0 {
            decCount = 1
            decJustTapped = true
        }
    }
    
    if title == plusMinusSym {
        // we don't want to display "-0"
        //  so only do this if...
        if currentValue != 0 {
            currentValue *= -1
        }
    }

    // clear the current value and
    //  reset decimal count
    if title == "C" {
        currentValue = 0
        decCount = 0
    }
    
    if operators.contains(title) {
        // perform operation...
    }
    
    udpateEntryLabel()
}

func udpateEntryLabel() {
    // this will handle entering "." followed by one or more Zeroes
    numFormatter.minimumFractionDigits = decCount - 1
    
    var str = numFormatter.string(from: currentValue as NSNumber) ?? "0"
    
    // this will only be true if the decimal symbol button was tapped
    //  but we do not yet have a fractional value
    if decJustTapped {
        decJustTapped = false
        str += "."
    }
    
    entryLabel.text = str
}

这是一个快速、完整的示例......

简单的按钮子类来获取“圆角”按钮：

class PillButton: UIButton {
    override func layoutSubviews() {
        super.layoutSubviews()
        layer.cornerRadius = bounds.height * 0.5
    }
}

视图控制器示例：

class CalcVC: UIViewController {
    
    let entryLabel = UILabel()
    
    let numFormatter: NumberFormatter = {
        let nf = NumberFormatter()
        nf.numberStyle = .decimal
        // we want ".1" to be displayed as "0.1"
        nf.minimumIntegerDigits = 1
        return nf
    }()

    var currentValue: Double = 0
    var decJustTapped: Bool = false
    var decCount: Int = 0

    // for clarity (tough to read division character and plus character)
    //  and, you'll probably want to localize the decimal character
    let plusMinusSym: String = "±"
    let pctSym: String = "%"
    let divideSym: String = "+"
    let multiplySym: String = "X"
    let minusSym: String = "-"
    let plusSym: String = "+"
    let decimalSym: String = "."
    let equalsSym: String = "="
    
    lazy var operators: [String] = [
        pctSym, divideSym, multiplySym, minusSym, plusSym, equalsSym
    ]

    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .systemBlue

        let btn = UIButton()
        let btnVal: Double = 0
        
        var curVal: Double = 0
        
        // user taps "5"
        curVal *= 10.0
        curVal += btnVal
        // cVal now equals 5
        
        // user taps "3"
        curVal *= 10.0
        curVal += btnVal
        // cVal now equals 53

        // user taps "7"
        curVal *= 10.0
        curVal += btnVal
        // cVal now equals 537
        
        // user taps "5"
        curVal *= 10.0
        curVal += btnVal
        // cVal now equals 5
        
        // user taps "+/-"
        curVal *= -1.0
        // cVal now equals -5
        
        // user taps "3"
        curVal *= 10.0
        curVal += curVal >= 0 ? btnVal : -btnVal
        // cVal now equals -53
        
        // user taps "7"
        curVal *= 10.0
        curVal += curVal >= 0 ? btnVal : -btnVal
        // cVal now equals -537
        
        // user taps "+/-" again
        curVal *= -1.0
        // cVal now equals 537
        

        let titles: [[String]] = [
            ["C", plusMinusSym, pctSym, divideSym],
            ["7", "8", "9", multiplySym],
            ["4", "5", "6", minusSym],
            ["1", "2", "3", plusSym],
            ["0", decimalSym, equalsSym],
        ]
        
        let stackView = UIStackView()
        stackView.axis = .vertical
        stackView.spacing = 6

        stackView.addArrangedSubview(entryLabel)
        
        for (iRow, rowTitles) in titles.enumerated() {
            let rowStack = UIStackView()
            rowStack.axis = .horizontal
            rowStack.distribution = .fillEqually
            rowStack.spacing = 6
            
            // handle bottom row differently because we have only 3 buttons
            if iRow == titles.count - 1 {
                
                let b = PillButton()
                b.addTarget(self, action: #selector(btnTapped(_:)), for: .touchUpInside)
                b.setTitle(rowTitles[0], for: [])
                b.setTitleColor(.white, for: .normal)
                b.setTitleColor(.lightGray, for: .highlighted)
                b.backgroundColor = .darkGray
                rowStack.addArrangedSubview(b)
                
                let rowStack2 = UIStackView()
                rowStack2.axis = .horizontal
                rowStack2.distribution = .fillEqually
                rowStack2.spacing = 6
                for j in 1..<rowTitles.count {
                    let b = PillButton()
                    b.addTarget(self, action: #selector(btnTapped(_:)), for: .touchUpInside)
                    b.setTitle(rowTitles[j], for: [])
                    b.setTitleColor(.white, for: .normal)
                    b.setTitleColor(.lightGray, for: .highlighted)
                    b.backgroundColor = j == 1 ? .darkGray : .systemOrange
                    b.heightAnchor.constraint(equalTo: b.widthAnchor, multiplier: 1.0).isActive = true
                    rowStack2.addArrangedSubview(b)
                }
                rowStack.addArrangedSubview(rowStack2)
                
            } else {
                rowTitles.forEach { s in
                    let b = PillButton()
                    b.addTarget(self, action: #selector(btnTapped(_:)), for: .touchUpInside)
                    b.setTitle(s, for: [])
                    b.setTitleColor(.white, for: .normal)
                    b.setTitleColor(.lightGray, for: .highlighted)
                    b.backgroundColor = .darkGray
                    b.heightAnchor.constraint(equalTo: b.widthAnchor, multiplier: 1.0).isActive = true
                    rowStack.addArrangedSubview(b)
                }
            }
            stackView.addArrangedSubview(rowStack)
        }
        
        // set background colors for non-darkGray buttons
        for i in 0..<stackView.arrangedSubviews.count - 1 {
            if let sv = stackView.arrangedSubviews[i] as? UIStackView,
               let v = sv.arrangedSubviews.last {
                v.backgroundColor = .systemOrange
            }
        }
        if let sv = stackView.arrangedSubviews[1] as? UIStackView {
            for i in 0..<3 {
                sv.arrangedSubviews[i].backgroundColor = .lightGray
            }
        }
        
        stackView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(stackView)
        
        let g = view.safeAreaLayoutGuide
    
        NSLayoutConstraint.activate([
            stackView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 20.0),
            stackView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -20.0),
            stackView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -20.0),
        ])

        // label properties
        entryLabel.font = .monospacedDigitSystemFont(ofSize: 24.0, weight: .regular)
        entryLabel.backgroundColor = UIColor(white: 0.95, alpha: 1.0)
        entryLabel.textAlignment = .right
        entryLabel.text = "0"
        
    }
    
    @objc func btnTapped(_ sender: UIButton) {
        
        guard let title = sender.currentTitle else { return }
        
        // if it's a number button
        if let val = Double(title) {
            var p: Double = 0
            var btnVal: Double = val

            // if "decimal count" is greater-than-Zero,
            //  we need to divide the input value by 10, 100, 1000, etc
            if decCount > 0 {
                p = pow(10.0, Double(decCount))
                btnVal /= p
                decCount += 1
            } else {
                currentValue *= 10.0
            }
            currentValue += currentValue >= 0 ? btnVal : -btnVal

            // if we have decimal values, we need to round the result
            //  due to floating-point precision
            //  e.g. if we enter "0" "." "1" "2"
            //  the actual value is 0.12000000000000002048
            //  so we round to the current number of decimal places
            if p > 0 {
                currentValue = round(currentValue * p) / p
            }
        }

        // if decimal button tapped
        if title == decimalSym {
            if decCount == 0 {
                decCount = 1
                decJustTapped = true
            }
        }
        
        if title == plusMinusSym {
            // we don't want to display "-0"
            //  so only do this if...
            if currentValue != 0 {
                currentValue *= -1
            }
        }

        // clear the current value and
        //  reset decimal count
        if title == "C" {
            currentValue = 0
            decCount = 0
        }
        
        if operators.contains(title) {
            // perform operation...
        }
        
        udpateEntryLabel()
    }
    
    func udpateEntryLabel() {
        // this will handle entering "." followed by one or more Zeroes
        numFormatter.minimumFractionDigits = decCount - 1
        
        var str = numFormatter.string(from: currentValue as NSNumber) ?? "0"
        
        // this will only be true if the decimal symbol button was tapped
        //  but we do not yet have a fractional value
        if decJustTapped {
            decJustTapped = false
            str += "."
        }
        
        entryLabel.text = str
    }
}

运行时看起来像这样：

请注意，仅实现了数字、小数、“C”和“+/-”按钮......我将把操作和“历史记录视图”任务留给你:)