Good Flutter User Name Validation

flutter_name_validation.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:form_builder_validators/form_builder_validators.dart';
import 'package:recase/recase.dart';

/// Custom TextInputFormatter that converts input to title case
class TitleCaseTextInputFormatter extends TextInputFormatter {
  @override
  TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue) {
    if (newValue.text.isEmpty || newValue.text.endsWith(' ')) {
      return newValue;
    }

    final titleCase = newValue.text.titleCase;

    return TextEditingValue(text: titleCase, selection: newValue.selection);
  }
}

/// A shared stateless widget for full name text field input.
///
/// This widget enforces consistent validation and formatting across the app
/// for full name inputs. It automatically converts input to title case and
/// filters out potentially dangerous characters.
class FullNameTextField extends StatelessWidget {
  const FullNameTextField({required this.controller, required this.onChanged, this.hintText = 'John Doe', super.key});

  final TextEditingController controller;
  final ValueChanged<String> onChanged;
  final String? hintText;

  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: controller,
      hintText: hintText ?? context.loc.fullNamePlaceholder,
      backgroundColor: const Color(0xFF000000),
      borderRadius: BorderRadius.circular(BorderRadiusConstants.normal),
      textStyle: context.textTheme.bodyMedium?.copyWith(color: Colors.white),
      validator: FormBuilderValidators.compose([
        FormBuilderValidators.required(),
        FormBuilderValidators.minLength(4, errorText: context.loc.fullNameMinLength),
      ]),
      inputFormatters: [
         // Remove any characters that are NOT valid in names
        // Allows: Unicode letters (\p{L}), combining marks/diacritics (\p{M}), numbers (\p{N}),
        // dots (.), apostrophes ('), hyphens (-), middle dot (·), glottal stop (ʔ), and spaces
        FilteringTextInputFormatter.deny(RegExp(r"[^\p{L}\p{M}\p{N}.'ʼʔ·\- ]+", unicode: true)),
        TitleCaseTextInputFormatter(),
      ],
      maxLength: 35,
      onChanged: onChanged,
    );
  }
}