在尝试 Widget of flutter 时，抛出 NoSuchMethodError 说 The method '_debugTypesAreRight' was called on null

Question

我正在尝试一个简单的 flutter dart 程序。我指的是本教程，我该如何解决这个问题？

获得以下异常

I/flutter ( 4785): ??? EXCEPTION CAUGHT BY WIDGETS LIBRARY ????????????????????????????????????????????????????????????
I/flutter ( 4785): The following NoSuchMethodError was thrown attaching to the render tree:
I/flutter ( 4785): The method '_debugTypesAreRight' was called on null.
I/flutter ( 4785): Receiver: null
I/flutter ( 4785): Tried calling: _debugTypesAreRight(Instance of 'RealWorldApp')

代码是：

import 'package:flutter/material.dart';

void main() => runApp(new RealWorldApp());

class RealWorldApp extends StatefulWidget {
  @override
  RealWorldState createState() => new RealWorldState();

}
 class RealWorldState extends State<RealWorldApp>
  {
  @override
  Widget build(BuildContext context) {
  return new MaterialApp(
    home: new Scaffold(
      appBar: new AppBar(
        title: new Text("First App"),
        actions: <Widget>[
          new IconButton(icon: new Icon(Icons.refresh),
          )
        ],
      ),
      body: new Center(
        child: new CircularProgressIndicator(),
      ),
    ),
  );
  }

  }

Answer 1

这是一个内部错误，而不是您的代码有问题。请尝试以下操作：

flutter upgrade &&           # use latest version
flutter packages get &&      # pub_get all packages
flutter clean &&             # delete caches
flutter build                # rebuild