How to input currency format on a text field (from right to left) using Swift?

Question

I have a number let’s say 0.00.

• When the user taps 1. We should have 0.01
• When the user taps 2. We should display 0.

Answer 1

Thanks to everyone here. From all the answers here I managed to come out with mine.

First I set up the initial value of the textField to be:

private func commonInit() { 
    amountTextField.text = "0.00"
}

Then I use the UITextFieldDelegate to get the input value and the current textview.text:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    //Need to check if the textfield.text can be evaluated as number or not before passing it to the function
    //Get the current text value, and current user input and pass it to the 
    let formattedAmount = formatAmount(oldAmount: textField.text, userInput: string)
    textField.text = formattedAmount
    return false
}

Here go my private function to format the number to move from right to left:

private func formatAmount(currentText: String, userInput: String) -> String {
    let amount = currentText.components(separatedBy: ".")
    var intValue: String = amount[0]
    var decimalValue: String = amount[1]
    

    //backspace registered, need to move the number to the right
    if userInput.isEmpty {
        decimalValue.remove(at: decimalValue.index(before: decimalValue.endIndex))
        decimalValue = intValue.last!.string + decimalValue
        intValue.remove(at: intValue.index(before: intValue.endIndex))
        if intValue.isEmpty {
            intValue = "0"
        }
    } else {
        
        //Need to consider if user paste value
        if userInput.count > 2 {
            decimalValue = String(userInput.suffix(2))
            intValue = String(userInput.dropLast(2))
        } else {
            decimalValue = rmAmount[1] + userInput
            
            //Add to int value (move to the right)
            intValue = intValue + decimalValue.first!.string
            
            if Int(intValue) == 0 {
                intValue = "0"      //00 -> 0
            } else if intValue.first == "0" {
                //remove 0 from at the first position in intValue
                intValue.remove(at: intValue.startIndex)    //01 -> 1
            }
            
            //Remove tenth place from decimal value since it goes to Int already
            decimalValue.remove(at: decimalValue.startIndex)
        }
    }
    return intValue + "." + decimalValue
}

This is basically it. Other extra implementations can be added by your own initiatives. Let me know if there is any problem with my implementation.

PS: This is of course only works for certain currency only, in my case, my apps is set up only for that local so thats why I use this way.