Question

我是新手，一直在尝试制作一个简单的测验应用程序。我遇到了一个错误，我不确定是什么错误。

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()                                                
                ^^^^^^

main.dart：

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()
              ],
            )));
  }
}

answer.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，并将正确的文件导入到main.dart中。我不知道怎么了。有人可以向我指出。预先感谢！

Answer 1

如果没有完整的最小程序复制和重现此行为的步骤，我将无法复制您收到的相同错误。在我的测试中，在main.dart中手动添加import 'answer.dart';并使用热重载运行该应用程序时发生了错误。由于这是热重载，并且手动添加了导入，因此很可能未包含代码更改，从而导致了问题。重新启动后，该应用程序运行正常，并且当您让IDE自动完成导入时，不会发生此问题。

根据当前的详细信息，我无法排除您的问题的确切原因。

我正在Flutter稳定频道1.22.0版上运行

我得到的错误：

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following _CompileTimeError was thrown building MyApp(dirty, state: _MyAppState#2340f):
Unimplemented handling of missing static target

The relevant error-causing widget was: 
  MyApp file:///Users/{USER}/Downloads/dev/flutter/sample60384439/lib/main.dart:5:23
When the exception was thrown, this was the stack: 
#0      StatefulElement.build (package:flutter/src/widgets/framework.dart:4744:28)
#1      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4627:15)
#2      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
#3      Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
#4      BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2730:33)
...
════════════════════════════════════════════════════════════════════════════════════════════════════
Reloaded 2 of 530 libraries in 220ms.

Answer 2

不一样，但类似的错误。我执行了热重启，而不是热重新加载。注意：Windows 10，Android Studio IDE

Answer 3

我不建议您自己编写导入，当您有一些未导入的小部件或函数时，将突出显示错误并指出修复建议。这是一个例子：

调用您的函数或小部件，这里我有一个小部件可调用：
如您所见，突出显示了一个错误，建议导入
单击该按钮，然后将小部件正确导入

这将在以后为您避免此类错误

Answer 4

我遇到了类似的问题。即使我的导入语句是正确的，我也遇到了这个问题。

然后我做了“flutter clean”并且在“flutter run”之后它起作用了。

因此，只需使用“flutter clean”清理构建并查看。希望它有效。

该方法未为该类定义-Flutter

4 个答案: