问参数类型'Function‘不能分配给参数类型'void ()？

EN

import 'package:flutter/material.dart';
import 'Questions.dart';
import 'answer.dart';

void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _MyAppState();
    // ignore: dead_code
    throw UnimplementedError();
  }
}

class _MyAppState extends State<MyApp> {
  var _questionIndex = 0;
  var questions = [
    'what\'s your fav color?',
    'what\'s your fav Food?',
    'what\'s your fav Animal?'
  ];
  

  void _answerQuestion() {
    setState(() {
      _questionIndex++;
      if (_questionIndex >= questions.length) _questionIndex = 0;
    });
    print(_questionIndex);
    print(questions.length);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My Flutter App'),
        ),
        body: Column(
          children: [
            Question(questions[_questionIndex]),
            Answer(_answerQuestion),
            Answer(_answerQuestion),
            Answer(_answerQuestion),
          ],
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';

class Answer extends StatelessWidget {
  final Function selectHandler;
  Answer(this.selectHandler);


  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      child: ElevatedButton(
        child: Text('Ans 1'),
        onPressed: selectHandler,
        style: ElevatedButton.styleFrom(
          primary: Colors.red,
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';

class Question extends StatelessWidget {
  final String questionText;
  Question(this.questionText);
  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      margin: EdgeInsets.all(10),
      padding: EdgeInsets.all(10),
      child: Text(
        questionText,
        style: TextStyle(fontSize: 28),
        textAlign: TextAlign.center,
      ),
    );
  }
}