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У меня есть main.dart, как показано ниже:

 //main.dart
import 'dart:io';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'src/loginPage.dart';
import 'src/tabsPage.dart';

void main() async {
  Widget _defaultPage = new LoginPage();
  runApp(MyApp(defaultPage: _defaultPage));
}

class MyApp extends StatelessWidget {
  final Widget defaultPage;

  const MyApp({Key key, @required this.defaultPage}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Gaia',
      debugShowCheckedModeBanner: false,
      home: defaultPage,
      routes: <String, WidgetBuilder>{
        '/tabs': (BuildContext context) => new TabsPage(),
        '/login': (BuildContext context) => new LoginPage(),
      },
    );
  }
}

//LoginPage.dart
import 'package:flutter/material.dart';
import '../main.dart';

class LoginPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => new _State();
}

class _State extends State<LoginPage> {
  TextEditingController userIdController = TextEditingController();
  TextEditingController passwordController = TextEditingController();

  void login() async {
     Navigator.of(context).pushReplacementNamed('/tabs');
  }

  void forgotPassword() {
    print("Forgot password!");
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Padding(
            padding: EdgeInsets.all(10),
            child: ListView(
              children: <Widget>[
                Container(
                    alignment: Alignment.center,
                    padding: EdgeInsets.all(40),
                    child: Text(
                      'Gaia',
                      style: TextStyle(
                          color: Colors.blue,
                          fontWeight: FontWeight.w500,
                          fontSize: 30),
                    )),
                Container(
                  padding: EdgeInsets.all(10),
                  child: TextField(
                    style: TextStyle(fontSize: 25),
                    maxLength: 6,
                    keyboardType: TextInputType.number,
                    controller: userIdController,
                    decoration: InputDecoration(
                      border: OutlineInputBorder(),
                      labelText: 'User Id',
                      labelStyle: TextStyle(fontSize: 25),
                      counter: Spacer(),
                    ),
                  ),
                ),
                Container(
                  padding: EdgeInsets.fromLTRB(10, 10, 10, 0),
                  child: TextField(
                    style: TextStyle(fontSize: 25),
                    obscureText: true,
                    controller: passwordController,
                    decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'password',
                        labelStyle: TextStyle(fontSize: 25)),
                  ),
                ),
                SizedBox(height: 50),
                Container(
                    padding: EdgeInsets.fromLTRB(100, 30, 100, 0),
                    child: RaisedButton(
                        child: Text(
                          'ログイン',
                          style: TextStyle(fontSize: 30),
                        ),
                        textColor: Colors.white,
                        color: Colors.blue,
                        onPressed: () {
                          login();
                        })),
                SizedBox(height: 120),
                FlatButton(
                  child: Text('Forgot password'),
                  onPressed: () {
                    forgotPassword();
                  },
                  textColor: Colors.blue,
                ),
                Container(
                  alignment: Alignment.center,
                  child: Text('Information'),
                ),
                Container(
                  alignment: Alignment.center,
                  child: Text('Here'),
                ),
              ],
            )));
  }
}
 

когда я запускаю его, который показывает мне предупреждающее сообщение, что я могу решить?

 ════════ Exception caught by widgets library ═══════════════════════════════════
The following assertion was thrown while applying parent data.:
Incorrect use of ParentDataWidget.

The ParentDataWidget Expanded(flex: 1) wants to apply ParentData of type FlexParentData to a RenderObject, which has been set up to accept ParentData of incompatible type BoxParentData.

Usually, this means that the Expanded widget has the wrong ancestor RenderObjectWidget. Typically, Expanded widgets are placed directly inside Flex widgets.
The offending Expanded is currently placed inside a _Decorator widget.

The ownership chain for the RenderObject that received the incompatible parent data was:
  SizedBox.shrink ← Expanded ← Spacer ← _Decorator ← InputDecorator ← AnimatedBuilder ← _PointerListener ← Listener ← RawGestureDetector ← TextSelectionGestureDetector ← ⋯
When the exception was thrown, this was the stack
#0      RenderObjectElement._updateParentData.<anonymous closure>
package:flutter/…/widgets/framework.dart:5770
#1      RenderObjectElement._updateParentData
package:flutter/…/widgets/framework.dart:5786
#2      RenderObjectElement.attachRenderObject
package:flutter/…/widgets/framework.dart:5808
#3      RenderObjectElement.mount
package:flutter/…/widgets/framework.dart:5501
#4      SingleChildRenderObjectElement.mount
package:flutter/…/widgets/framework.dart:6117
...