如何替换 UITextField 中字符串中的特定字符？

Question

赏金将在 7 天后到期。 此问题的答案有资格获得+50声望赏金。 artexhibit想引起更多关注这个问题：

我真的坚持这个问题，希望任何人都可以查看我的代码并给出一些工作示例或解释我如何正确地完成这部分。

我希望我的 textField 做什么：1）它可以在最大（完成）时具有“数字 + 数字”格式 2）每个数字都应该用 NSNumberFormatter 格式化（完成），3）用户可以在第一个数字之后键入数学符号并更改它自由，直到他输入第二个数字（我遇到的问题）4）如果用户在输入数字+数字后输入数学符号，应该有一个显示新数字和数学符号的计算（尚未完成）

谢谢！

我有一个自定义 textField 的输入视图 - 它是一个Numpad风格的键盘。 Numpad用于将数字和数学符号添加到textField 。

如果用户已经添加了一个数学符号并想立即在另一个上更改它，我无法弄清楚如何更改字符串中的数学符号。 这是我需要的一个例子：

这是我使用的代码：

 func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

//number formatter
let formatter = NumberFormatter()
formatter.numberStyle = .decimal
formatter.maximumFractionDigits = 2
formatter.locale = .current
formatter.roundingMode = .down

//all possible math operation symbols user can add
let symbolsSet = Set(["+","-","x","/"])
var amountOfSymbols = 0

let numberString = textField.text ?? ""
guard let range = Range(range, in: numberString) else { return false }
let updatedString = numberString.replacingCharacters(in: range, with: string)
let correctDecimalString = updatedString.replacingOccurrences(of: formatter.groupingSeparator, with: "")
let completeString = correctDecimalString.replacingOccurrences(of: formatter.decimalSeparator, with: ".")

//current math symbol user add
let symbol = symbolsSet.filter(completeString.contains).last ?? ""
//if user add math symbol to an empty string - do not insert
if string == symbol, numberString.count == 0 { return false }

//count how much math symbols string has. If more that one - do not insert, string can have only one
completeString.forEach { character in
    if symbolsSet.contains(String(character)) {
        amountOfSymbols += 1
    }
}
if amountOfSymbols > 1 { return false }

//count how much decimals string has. If more that one - do not insert because it can have only one per number
let numbersArray = completeString.components(separatedBy: symbol)
for number in numbersArray {
    let amountOfDecimalSigns = number.filter({$0 == "."}).count
    if amountOfDecimalSigns > 1 { return false }
}

//create numbers from a string
guard let firstNumber = Double(String(numbersArray.first ?? "0")) else { return true }
guard let secondNumber = Double(String(numbersArray.last ?? "0")) else { return true }

//format numbers and turn them back to string
let firstFormattedNumber = formatter.string(for: firstNumber) ?? ""
let secondFormattedNumber = formatter.string(for: secondNumber) ?? ""

//assign formatted numbers to a textField
textField.text = completeString.contains(symbol) ? "\(firstFormattedNumber)\(symbol)\(secondFormattedNumber)" : "\(firstFormattedNumber)"

return string == formatter.decimalSeparator
}

我的逻辑是使用textField.deleteBackwards()方法删除一个旧的并在之后添加一个新的数学符号，但是使用上面的代码它不起作用：它删除了符号，但没有出现一个新的符号 - 我应再次按下，以便出现新符号。

我应该怎么做才能更改字符串中的数学符号？

GitHub上的测试项目

更新：

我能得到的最接近的工作解决方案是：

     var completeString = correctDecimalString.replacingOccurrences(of: formatter.decimalSeparator, with: ".")

        //count how much math symbols string has. If more than one - do not insert, string can have only one
    completeString.forEach { character in
        if symbolsSet.contains(String(character)) {
            amountOfSymbols += 1
        }
    }
    
    if amountOfSymbols > 1 {
        let newSymbol = completeString.last?.description ?? ""
        completeString.removeAll { symbolsSet.contains(String($0))}
        textField.text = completeString+newSymbol
        return false
    }

但是当我添加第二个数字并再次按下数学符号时出现问题：

也许我的方法是错误的？ 怎么做才对？

Answer 1

您应该为您的 UITextView 文本更改添加一个侦听器。

NotificationCenter.default.addObserver(forName: UITextField.textDidChangeNotification, object: myTextField, queue: OperationQueue.main) { [weak self] (notification) in
    guard let self = self else { return }
            
    guard let textField = notification.object as? UITextField else { return }
            
    //here write a logic which verifies if the last character in the text is one of the mathematical symbols, and the one previous to that is also a math symbol, then you would replace the 'lastIndex - 1' with the last character
    guard let text = textField.text, text.count > 2 else { return }
    guard let lastChar = text.last else { return }
    let previousChar: Character = Array(text)[text.count - 2]
    //compare these two characters and make sure the 'previousChar' is a math symbol but not a number, if so - replace it with 'lastChar'
}

Answer 2

在shouldChangeCharactersIn委托中使用如下逻辑。

     
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        
        var shouldChange : Bool = true
        
        //current text visible in the text field
        let numberString = textField.text ?? ""
        
        //last charachter in the text field
        let lastCharachter = numberString.last
        
        //get all the numbers displayed in the textfield by sperating them from symbols
        let numbersArray = numberString.components(separatedBy: CharacterSet(charactersIn: "+-x/"))
        
        
        if string == ""{
            
        }
        
        //stop entering a symbol in the first place
        else if numberString == ""{
            if !Character(string).isNumber{
                shouldChange = false
            }
        }
        
        //if a number is entered check for the decimal points
        else if Character(string).isNumber{
            if numbersArray.last!.contains(".") && numbersArray.last?.components(separatedBy: ".").last?.count == 2 && Character(string).isNumber{
                shouldChange =  false
            }
        // if symbol is entered
        }else{
            if string == "."{
                if !lastCharachter!.isNumber{
                    shouldChange = false
                }
            }

            //if there are more than 1 numbers numbersArray, calculate the value
            else if lastCharachter!.isNumber{
                if numbersArray.count > 1{
                    let expression = NSExpression(format: numberString)
                    let answer =  expression.expressionValue(with:nil, context: nil) as! Double
                    textField.text = "\(forTrailingZero(temp: answer))\(string)"
                    shouldChange = false
                }
            }else{
                //change the symbol
                textField.text = "\(textField.text!.dropLast())\(string)"
                shouldChange =  false
            }
        }
        
        return shouldChange
    }
    
    //use to remove trailing zeros
    func forTrailingZero(temp: Double) -> String {
        let tempVar = String(format: "%g", temp)
        return tempVar
    }

实现预期输出可能有不同的方法。