formatEditUpdate method

@override TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue)

Creates a formatter that allows only digits.

Implementation

@override
TextEditingValue formatEditUpdate(
  TextEditingValue oldValue, // The previous value of the text field.
  TextEditingValue newValue, // The new value of the text field.
) {
  // If the new value is empty, allow it.
  if (newValue.text.isEmpty) {
    return newValue;
  }

  // Use a regular expression to remove all non-digit characters.
  final String newText = newValue.text.replaceAll(RegExp(r'\D'), '');

  // If the new value is different from the old one, update the text field.
  if (newText != newValue.text) {
    return TextEditingValue(
      text: newText,
      selection: TextSelection.collapsed(offset: newText.length),
    );
  }

  // Otherwise, return the new value as is.
  return newValue;
}