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,
) {
  if (newValue.text.isEmpty) {
    return newValue;
  }

  final String latin = newValue.text.toLatinNumber();

  final StringBuffer result = StringBuffer();

  int digitCount = 0;
  int cursorPosition = 0;

  final int requestedCursor = newValue.selection.baseOffset;

  for (int i = 0; i < latin.length; i++) {
    final String character = latin[i];

    if (character.codeUnitAt(0) >= 48 && character.codeUnitAt(0) <= 57) {
      if (digitCount >= maxDigits) {
        break;
      }

      result.write(character);
      digitCount++;

      if (i < requestedCursor) {
        cursorPosition++;
      }
    }
  }

  final String formatted = result.toString();

  cursorPosition = cursorPosition.clamp(0, formatted.length);

  return TextEditingValue(
    text: formatted,
    selection: TextSelection.collapsed(
      offset: cursorPosition,
    ),
  );
}