【flutter】Error: The non-abstract class 'MyApp' is missing implementations for these members:

解決したい課題

下記エラーを解消したい。

エラー

lib/main.dart:9:7: Error: The non-abstract class 'MyApp' is missing implementations for these members:
 - StatefulWidget.createState
Try to either
 - provide an implementation,
 - inherit an implementation from a superclass or mixin,
 - mark the class as abstract, or
 - provide a 'noSuchMethod' implementation.

class MyApp extends StatefulWidget {
      ^^^^^
/C:/src/flutter/packages/flutter/lib/src/widgets/framework.dart:925:9: Context: 'StatefulWidget.createState' is defined here.
  State createState();
        ^^^^^^^^^^^
lib/main.dart:61:7: Error: The non-abstract class 'NextPage' is missing implementations for these members:
 - StatefulWidget.createState
Try to either
 - provide an implementation,
 - inherit an implementation from a superclass or mixin,
 - mark the class as abstract, or
 - provide a 'noSuchMethod' implementation.

class NextPage extends StatefulWidget{
      ^^^^^^^^
/C:/src/flutter/packages/flutter/lib/src/widgets/framework.dart:925:9: Context: 'StatefulWidget.createState' is defined here.
  State createState();
        ^^^^^^^^^^^
lib/main.dart:75:7: Error: The non-abstract class 'NextPage2' is missing implementations for these members:
 - StatefulWidget.createState
Try to either
 - provide an implementation,
 - inherit an implementation from a superclass or mixin,
 - mark the class as abstract, or
 - provide a 'noSuchMethod' implementation.

class NextPage2 extends StatefulWidget{
      ^^^^^^^^^
/C:/src/flutter/packages/flutter/lib/src/widgets/framework.dart:925:9: Context: 'StatefulWidget.createState' is defined here.
  State createState();
        ^^^^^^^^^^^
lib/main.dart:30:29: Error: 'setState' isn't a function or method and can't be invoked.
                    setState((){
                            ^^^^^...

コード

//入力画面
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

// ignore: must_be_immutable
class MyApp extends StatefulWidget {
  String name;
  String setState;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        theme: ThemeData(
          primarySwatch: Colors.blue,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: Scaffold(
          appBar: AppBar(
            title: Text('入力画面'),
          ),
          body: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                TextField(
                  onChanged: (value) {
                    setState((){
                      name = value;
                    });
                  },
                  decoration: InputDecoration(
                      hintText: 'ここに入力した値を次の画面に渡したい'
                  ),
                ),
                TextField(
                  decoration: InputDecoration(
                      hintText: 'ここに入力した値を次の画面に渡したい'
                  ),
                ),
                RaisedButton(
                    child: Text('確認画面へ'),
                    onPressed: (){
                      Navigator.push(
                        context,
                        MaterialPageRoute(builder: (context) => NextPage()),
                      );
                    }
                ),
              ],
            ),
          ),
        )
    );
  }
}

//確認画面
class NextPage extends StatefulWidget{

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        theme: ThemeData(
          primarySwatch: Colors.blue,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: NextPage2(),
    );
  }
}

class NextPage2 extends StatefulWidget{
  NextPage2({this.name});
  final String name;

  @override
  Widget build(BuildContext context){
    return Scaffold(
      appBar: AppBar(
        title: Text('確認画面'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(name),
            Text(name),
          ],
        ),
      ),
    );
  }
}

何が間違っているのかエラー見ても不明です。
どなたかアドバイスいただけませんでしょうか。
よろしくお願いいたします。

追記

//入力画面
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

// ignore: must_be_immutable
class MyApp extends StatefulWidget {
  String name;
  String phone;

  MyApp({Key key, this.name, this.phone}) : super(key: key);

  @override
  MyAppState createState() => MyAppState();
}
class MyAppState extends State<MyApp> {
  Widget build(BuildContext context) {
    return MaterialApp(
        theme: ThemeData(
          primarySwatch: Colors.blue,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: Scaffold(
          appBar: AppBar(
            title: Text('入力画面'),
          ),
          body: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                TextField(
                  onChanged: (value) {
                    setState((){
                      name = value;
                    });
                  },
                  decoration: InputDecoration(
                      hintText: 'ここに入力した値を次の画面に渡したい'
                  ),
                ),
                TextField(
                  decoration: InputDecoration(
                      hintText: 'ここに入力した値を次の画面に渡したい'
                  ),
                ),
                RaisedButton(
                    child: Text('確認画面へ'),
                    onPressed: (){
                      Navigator.push(
                        context,
                        MaterialPageRoute(builder: (context) => NextPage()),
                      );
                    }
                ),
              ],
            ),
          ),
        )
    );
  }
}

//確認画面
class NextPage extends StatefulWidget{

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: NextPage2(),
    );
  }
}

class NextPage2 extends StatefulWidget{
  NextPage2({this.name});
  final String name;

  @override
  Widget build(BuildContext context){
    return Scaffold(
      appBar: AppBar(
        title: Text('確認画面'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(name),
            Text(name),
          ],
        ),
      ),
    );
  }
}