如何修复颤振 lib/main.dart 错误

Question

我是 Flutter 的初学者，这是我的第一个项目。我使用命令 flutter create 设置了一个新项目，然后我遇到了多个问题，我使用flutter doctor -v 修复了这些问题，但现在我遇到了这些错误，我似乎无法找到解决它们的方法，每次我运行颤振运行 Running Gradle task 'assembleDebug'... 需要很长时间，然后出现以下错误：

Launching lib\main.dart on sdk gphone x86 in debug mode...
Running Gradle task 'assembleDebug'...
lib/main.dart:7:37: Error: Can't find '}' to match '{'.
class MyApp extends StatelessWidget {
                                    ^
lib/main.dart:33:1: Error: Classes can't be declared inside other classes.
Try moving the class to the top-level.
class MyHomePage extends StatefulWidget {
^^^^^
lib/main.dart:33:18: Error: Expected a class member, but got 'extends'.
class MyHomePage extends StatefulWidget {
                 ^^^^^^^
lib/main.dart:33:26: Error: A method declaration needs an explicit list of parameters.
Try adding a parameter list to the method declaration.
class MyHomePage extends StatefulWidget {
                         ^^^^^^^^^^^^^^
lib/main.dart:51:1: Error: Classes can't be declared inside other classes.
Try moving the class to the top-level.
class _MyHomePageState extends State<MyHomePage> {
^^^^^
lib/main.dart:51:24: Error: Expected a class member, but got 'extends'.
class _MyHomePageState extends State<MyHomePage> {
                       ^^^^^^^
lib/main.dart:51:32: Error: A method declaration needs an explicit list of parameters.
Try adding a parameter list to the method declaration.
class _MyHomePageState extends State<MyHomePage> {
                               ^^^^^
lib/main.dart:29:13: Error: The method 'MyHomePage' isn't defined for the class 'MyApp'.
 - 'MyApp' is from 'package:new_app/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing method, or defining a method named 'MyHomePage'.
      home: MyHomePage(title: 'Flutter Demo Home Page'),
            ^^^^^^^^^^
lib/main.dart:34:19: Error: Expected ',' before this.
  MyHomePage({Key key, this.title}) : super(key: key);
                  ^^^
lib/main.dart:34:35: Error: Expected ';' after this.
  MyHomePage({Key key, this.title}) : super(key: key);
                                  ^
lib/main.dart:34:37: Error: Expected an identifier, but got ':'.
  MyHomePage({Key key, this.title}) : super(key: key);
                                    ^
lib/main.dart:34:37: Error: Expected ';' after this.
  MyHomePage({Key key, this.title}) : super(key: key);
                                    ^
lib/main.dart:34:37: Error: Unexpected token ';'.
  MyHomePage({Key key, this.title}) : super(key: key);
                                    ^
lib/main.dart:34:39: Error: Can't use 'super' as an expression.
To delegate a constructor to a super constructor, put the super call as an initializer.
  MyHomePage({Key key, this.title}) : super(key: key);
                                      ^
lib/main.dart:45:16: Error: The final variable 'title' must be initialized.
Try adding an initializer ('= expression') to the declaration.
  final String title;
               ^^^^^
lib/main.dart:48:3: Error: '_MyHomePageState' isn't a type.
  _MyHomePageState createState() => _MyHomePageState();
  ^^^^^^^^^^^^^^^^
lib/main.dart:34:3: Error: The method 'MyHomePage' isn't defined for the class 'MyApp'.
 - 'MyApp' is from 'package:new_app/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing method, or defining a method named 'MyHomePage'.
  MyHomePage({Key key, this.title}) : super(key: key);
  ^^^^^^^^^^
lib/main.dart:34:29: Error: The getter 'title' isn't defined for the class 'MyApp'.
 - 'MyApp' is from 'package:new_app/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'title'.
  MyHomePage({Key key, this.title}) : super(key: key);
                            ^^^^^
lib/main.dart:48:37: Error: The method '_MyHomePageState' isn't defined for the class 'MyApp'.
 - 'MyApp' is from 'package:new_app/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing method, or defining a method named '_MyHomePageState'.
  _MyHomePageState createState() => _MyHomePageState();
                                    ^^^^^^^^^^^^^^^^
lib/main.dart:55:5: Error: The method 'setState' isn't defined for the class 'MyApp'.
 - 'MyApp' is from 'package:new_app/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing method, or defining a method named 'setState'.
    setState(() {
    ^^^^^^^^
lib/main.dart:77:21: Error: The getter 'widget' isn't defined for the class 'MyApp'.
 - 'MyApp' is from 'package:new_app/main.dart' ('lib/main.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'widget'.
        title: Text(widget.title),
                    ^^^^^^


FAILURE: Build failed with an exception.

* Where:
Script 'I:\Programs\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 904

* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command 'I:\Programs\flutter\bin\flutter.bat'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 13m 24s
Exception: Gradle task assembleDebug failed with exit code 1

Answer 1

我找到了一个解决方案，flutter 和 dart 插件已安装在 android studio 中，但每次我运行 flutter -v 时都会收到未安装的错误，因此我使用以下步骤修复了它

flutter upgrade

flutter config --android-studio-dir="C:\Program Files\Android\Android Studio"

flutter doctor -v
    
flutter channel beta

flutter upgrade

然后我创建了一个新项目并启动它并且它工作了