formatEditUpdate method

@override TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue)

Called when text is being typed or cut/copy/pasted in the EditableText.

You can override the resulting text based on the previous text value and the incoming new text value.

When formatters are chained, oldValue reflects the initial value of TextEditingValue at the beginning of the chain.

Implementation

@override
TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue) {
  // Remove any non-digit characters from the input
  String unmaskedText = newValue.text.replaceAll(RegExp(r'\D'), '');

  // Create a masked version of the credit card number
  String maskedText = '';
  for (int i = 0; i < unmaskedText.length; i++) {
    maskedText += unmaskedText[i];
    if ((i + 1) % 2 == 0 && i != unmaskedText.length - 1) {
      maskedText += '/'; // Add a space every 4 characters
    }
  }

  return TextEditingValue(
    text: maskedText,
    selection: TextSelection.collapsed(offset: maskedText.length),
  );
}