我正在尝试将一个Hive从主屏幕传递到下一个，但无法。我试着在materialpageroute时使用box类型，但没有成功。
我正在接受来自用户的数据并尝试对其执行crud操作。我还想把一个Hive从一页传递到下一页

import 'dart:io';
import 'package:flutter/material.dart';
import 'package:fluttertoast/fluttertoast.dart';
import 'package:hive/hive.dart';
import 'package:path_provider/path_provider.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  Directory dir = await getExternalStorageDirectory();
  Hive.init(dir.path);
  print(dir.path);
  await Hive.openBox<String>('box1');
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Hive Storage Test Run'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String name, pass;

  Box<String> box2;

  TextEditingController _fullname = TextEditingController();
  TextEditingController _password = TextEditingController();

  @override
  void initState() {
    super.initState();
    box2 = Hive.box<String>('box1');
  }

  bool _showpass = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            //Full name
            TextField(
              controller: _fullname,
              decoration: InputDecoration(labelText: 'Enter Full name'),
              onSubmitted: (String value) {
                name = value;
                Fluttertoast.showToast(msg: 'Welcome ${name}');
              },
            ),
            //Password
            TextField(
              controller: _password,
              obscureText: !this._showpass,
              decoration: InputDecoration(
                labelText: 'Enter Password',
                suffixIcon: IconButton(
                  icon: Icon(
                    Icons.remove_red_eye_outlined,
                    color: this._showpass ? Colors.redAccent : Colors.blueAccent,
                  ),
                  onPressed: () {
                    setState(() => this._showpass = !this._showpass);
                  },
                ),
              ),
              onSubmitted: (String value) {
                pass = value;
                Fluttertoast.showToast(msg: 'Password is ${pass}');
              },
            ),
            SizedBox(height: 100,),
            Column(
              children: <Widget>[
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  children: <Widget>[
                    RaisedButton(
                      child: Text('Save'),
                      onPressed: () {
                        final key = _fullname.text;
                        final value = _password.text;
                        box2.put(key, value);
                        print(key);
                        print(value);
                        setState(() {
                          _fullname = TextEditingController(text: "");
                          _password = TextEditingController(text: "");
                        });
                      },
                    ),
                    RaisedButton(
                      child: Text('Print Values'),
                      onPressed: () {
                        print(box2.getAt(0));
                      },
                    ),
                  ],
                ),
                SizedBox(height: 30.0,),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  children: <Widget>[
                    RaisedButton(
                      child: Text('Load'),
                      onPressed: () {
                        if(box2.isEmpty == true){
                          Fluttertoast.showToast(msg: "No data present. Please enter new data");
                        }else{
                          Box box3 = box2;
                          Navigator.of(context)
                              .push(
                            MaterialPageRoute(
                              builder: (context) => Page2(box3: box3),
                            )
                          );
                        }
                      },
                    ),
                    RaisedButton(
                      child: Text("Empty Data"),
                      onPressed: () {
                        box2.clear();
                      },
                    ),
                  ],
                ),
              ],
            ),
          ],
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class Page2 extends StatefulWidget {

  Box box3;
  Page2({box3});

  @override
  _Page2State createState() => _Page2State(box3);
}

class _Page2State extends State<Page2> {

  Box box3;
  _Page2State(this.box3);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Page 2"),
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            Text("Page 2"),
            Text(box3.getAt(0)),
            RaisedButton(
              onPressed: () {
                child: Text("Back");
                Navigator.of(context).pop();
              },
            )
          ],
        ),
      ),
    );
  }
}

我需要把第二栏从我的主页转到第二页
这是我的错。。。。

The following NoSuchMethodError was thrown building Page2(dirty, state: _Page2State#33882):
The method 'getAt' was called on null.
Receiver: null
Tried calling: getAt(0)

The relevant error-causing widget was: 
  Page2 file:///C:/Users/harsh/AndroidStudioProjects/storage/lib/main.dart:142:53
When the exception was thrown, this was the stack: 

# 0      Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)

# 1      _Page2State.build (package:storage/main.dart:190:23)

# 2      StatefulElement.build (package:flutter/src/widgets/framework.dart:4744:28)

# 3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4627:15)

# 4      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)

...