我希望你会觉得这对你有帮助

class ValueCalculator extends StatefulWidget {
  const ValueCalculator({super.key});

  @override
  State<StatefulWidget> createState() => _ValueCalculatorState();
}

class _ValueCalculatorState extends State<ValueCalculator> {
  final TextEditingController _inputText = TextEditingController();

  final Map<int, int> map = {};

  String results = "0";
  String inputText = "";

  _ValueCalculatorState() {
    for (var i = 1, j = 'a'.codeUnits.first;
        j <= 'z'.codeUnits.first;
        i++, j++) {
      map[j] = i;
    }

    for (var i = 0, j = '0'.codeUnits.first;
        j <= '9'.codeUnits.first;
        i++, j++) {
      map[j] = i;
    }
  }

  @override
  void initState() {
    super.initState();
    _inputText.addListener(_onInputTextChanged);
  }

  void _onInputTextChanged() => inputText = _inputText.text;

  void _clearTextField() {
    _inputText.clear();
    setState(() {});
  }

  int _calculate(String input) {
    int result = 0;

    for (var i = 0; i < input.codeUnits.length; i++) {
      final key = input.codeUnitAt(i);
      final value = map[key];
      if (value != null) {
        result += value;
      }
    }

    while (result > 9) {
      int sumOfDigits = 0;
      for (int i = result; i > 0; i ~/= 10) {
        sumOfDigits += i.remainder(10);
      }

      result = sumOfDigits;
    }

    return result;
  }

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () => FocusManager.instance.primaryFocus?.unfocus(),
      child: Scaffold(
        body: SingleChildScrollView(
          child: SafeArea(
            child: Padding(
              padding: const EdgeInsets.all(10.0),
              child: Column(
                children: [
                  TextFormField(
                    controller: _inputText,
                    minLines: 5,
                    maxLines: 9,
                    keyboardType: TextInputType.multiline,
                    decoration: InputDecoration(
                      labelText: 'Enter Text ',
                      border: OutlineInputBorder(
                        borderRadius: BorderRadius.circular(10.0),
                      ),
                    ),
                  ),
                  const Padding(
                    padding: EdgeInsets.symmetric(
                      vertical: 20.0,
                      horizontal: 20.0,
                    ),
                  ),
                  Text(
                    results,
                    style: const TextStyle(fontSize: 50),
                  ),
                  const Padding(
                    padding: EdgeInsets.symmetric(
                      vertical: 20.0,
                      horizontal: 20.0,
                    ),
                  ),
                  ElevatedButton(
                    onPressed: () {
                      setState(() {
                        results =
                            _calculate(inputText.toLowerCase()).toString();
                      });
                    },
                    style: ElevatedButton.styleFrom(
                      padding: const EdgeInsets.symmetric(
                        vertical: 25,
                        horizontal: 60,
                      ),
                    ),
                    child: const Text("Calculate"),
                  ),
                  const Padding(
                    padding: EdgeInsets.symmetric(
                      vertical: 20.0,
                      horizontal: 20.0,
                    ),
                  ),
                  ElevatedButton(
                    onPressed: () {
                      results = "0";
                      _clearTextField();
                    },
                    style: ElevatedButton.styleFrom(
                      padding: const EdgeInsets.symmetric(
                        vertical: 15,
                        horizontal: 30,
                      ),
                    ),
                    child: const Text("Reset"),
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }

  @override
  void dispose() {
    _inputText.removeListener(_onInputTextChanged);
    _inputText.dispose();
    super.dispose();
  }
}

更新计算按钮的onPressed（）方法，如下所示：它将解决这两个问题，考虑数字和空字符串显示0

onPressed: () {
// calculation logic
   value = inputText.replaceAll(RegExp('[^A-Za-z0-9]'), '');
   int sum = 0;
   if (value.trim().isNotEmpty) {
       for (int i = 0; i < value.length; i++) {
            if (_isNumeric(value[i]) == true) {
                sum += int.parse(value[i]);
            } else {
              (value[i].toUpperCase() == value[i])
                     ? sum += (value.codeUnitAt(i) - 64)
                      : sum += (value.codeUnitAt(i) - 96);
           }
       }
    }
   setState(() {
      results = sum.toString() != "" ? sum.toString() : "0";
   });
}

//isNumeric func
 bool _isNumeric(String result) {
    return int.tryParse(result) != null;
  }