sign_up_screen.dart

Future<void> _signUpUser() async {
  if (_formKey.currentState!.validate()) {
    // (1)
    setState(() {
      _isLoading = true;
      _errorMessage = null;
    });
    try {
      final result = await Amplify.Auth.signUp(
        username: _usernameController.text,
        password: _passwordController.text,
        options: CognitoSignUpOptions(
          userAttributes: <CognitoUserAttributeKey, String>{
            CognitoUserAttributeKey.email: _emailController.text,
          },
        ),
      );
      // (2)
      if (result.nextStep.signUpStep == CognitoSignUpStep.confirmSignUp.value) {
        // (3)
        if (mounted) {
          context.go(
            '/confirm-user',
            extra: _usernameController.text,
          );
        }
      }
      // (4)
      setState(() {
        _isLoading = false;
      });
      // (5)
      _usernameController.clear();
      _emailController.clear();
      _passwordController.clear();
      // (6)
    } on UsernameExistsException {
      setState(() {
        _isLoading = false;
        _errorMessage = 'Username already exists. Please pick a different one.';
      });
    } on Exception catch(error) {
      setState(() {
        _isLoading = false;
        _errorMessage = 'An unexpected error has happened. Check the logs for detail';
      });
      logger.error(error.toString());
    }
  }
}