我是flutter的新手，一直在尝试做一个简单的问答应用程序。我遇到了一个错误，我不知道是什么错误。

• • 错误：**

Compiler message:                                                       
lib/main.dart:37:17: Error: The method 'Answer' isn't defined for the class '_MyAppState'.
 - '_MyAppState' is from 'package:project2/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing method, or defining a method named 'Answer'.
                Answer(),                                               
                ^^^^^^                                                  
lib/main.dart:38:17: Error: The method 'Answer' isn't defined for the class '_MyAppState'.
 - '_MyAppState' is from 'package:project2/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing method, or defining a method named 'Answer'.
                Answer(),                                               
                ^^^^^^                                                  
lib/main.dart:39:17: Error: The method 'Answer' isn't defined for the class '_MyAppState'.
 - '_MyAppState' is from 'package:project2/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing method, or defining a method named 'Answer'.
                Answer()                                                
                ^^^^^^

• • 主省道：**

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();
  }
}

class _MyAppState extends State<MyApp> {
  var _questionIndex = 0;

  var _questions = ["Question 1?", "Question 2?", "Question 3?"];

  void _answerQuestion() {
    setState(() {
      _questionIndex = _questionIndex + 1;
    });

    print("You answered the question!");
  }

  Widget build(BuildContext context) {
    return MaterialApp(
        home: Scaffold(
            appBar: AppBar(
              title: Text("Quiz"),
            ),
            body: Column(
              children: <Widget>[
                Question(_questions[_questionIndex]),
                Answer(),
                Answer(),
                Answer()
              ],
            )));
  }
}

• • 答案。 dart ：**

import 'package:flutter/material.dart';

class Answer extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Container(
        width: double.infinity,
        color: Colors.blue,
        child: RaisedButton(child: Text("Answer 1"), onPressed: null));
  }
}

我使用了相同的类名，并且导入了正确的文件到main.dart中。我不确定是什么问题。请有人给我指出。提前感谢!