formatEditUpdate method Null safety

  1. @override
TextEditingValue formatEditUpdate(
  1. TextEditingValue oldValue,
  2. 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.


TextEditingValue formatEditUpdate(
  TextEditingValue oldValue,
  TextEditingValue newValue,
) {
  final int? maxLength = this.maxLength;

  if (maxLength == null ||
    maxLength == -1 ||
    newValue.text.characters.length <= maxLength) {
    return newValue;

  assert(maxLength > 0);

  switch (maxLengthEnforcement ?? getDefaultMaxLengthEnforcement()) {
    case MaxLengthEnforcement.none:
      return newValue;
    case MaxLengthEnforcement.enforced:
      // If already at the maximum and tried to enter even more, and has no
      // selection, keep the old value.
      if (oldValue.text.characters.length == maxLength && oldValue.selection.isCollapsed) {
        return oldValue;

      // Enforced to return a truncated value.
      return truncate(newValue, maxLength);
    case MaxLengthEnforcement.truncateAfterCompositionEnds:
      // If already at the maximum and tried to enter even more, and the old
      // value is not composing, keep the old value.
      if (oldValue.text.characters.length == maxLength &&
        !oldValue.composing.isValid) {
        return oldValue;

      // Temporarily exempt `newValue` from the maxLength limit if it has a
      // composing text going and no enforcement to the composing value, until
      // the composing is finished.
      if (newValue.composing.isValid) {
        return newValue;

      return truncate(newValue, maxLength);