FilteringTextInputFormatter class

A TextInputFormatter that prevents the insertion of characters matching (or not matching) a particular pattern, by replacing the characters with the given replacementString.

Instances of filtered characters found in the new TextEditingValues will be replaced by the replacementString which defaults to the empty string, and the current TextEditingValue.selection and TextEditingValue.composing region will be adjusted to account for the replacement.

This formatter is typically used to match potentially recurring Patterns in the new TextEditingValue. It never completely rejects the new TextEditingValue and falls back to the current TextEditingValue when the given filterPattern fails to match. Consider using a different TextInputFormatter such as:

// _pattern is a RegExp or other Pattern object
TextInputFormatter.withFunction(
  (TextEditingValue oldValue, TextEditingValue newValue) {
    return _pattern.hasMatch(newValue.text) ? newValue : oldValue;
  },
),

for accepting/rejecting new input based on a predicate on the full string. As an example, FilteringTextInputFormatter typically shouldn't be used with RegExps that contain positional matchers (^ or $) since these patterns are usually meant for matching the whole string.

Quote characters on iOS

When filtering single (') or double (") quote characters, be aware that the default iOS keyboard actually inserts special directional versions of these characters (‘ and ’ for single quote, and “ and ” for double quote). Consider including all three variants in your regular expressions to support iOS.