Hive Flutter Usage

I am a newbee at Flutter and Hive, just learning. Here are some questions:

1. I am using Value Listenable Builder, when I press the "Person age Up" person1 age is not updated, but if I press the setstate then is updated. How to auto update?

2. Hive is a database; if I press the "Add person", it adds, and I see when I press "Print person lenght" but when reloaded the app person length is changed to 1 again, all adds removed:

import 'package:flutter/material.dart';
import 'package:hive/hive.dart';
import 'package:hive_flutter/hive_flutter.dart';
import 'departmentClass.dart';
import 'person.dart';

void main() async {
  await Hive.initFlutter('test');
  Hive.registerAdapter(DepartmentAdapter());
  Hive.registerAdapter(PersonAdapter());
  await Hive.openBox<Department>('testBox');

  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final Box testBox = Hive.box<Department>('testBox');

  @override
  Widget build(BuildContext context) {
    if (testBox.isEmpty) {
      final List<Person> personsAll = [];

      final person1 = new Person(23, "Maria");
      personsAll.add(person1);
      var mydepartment = new Department(34, "newD", personsAll);

      Hive.box<Department>('testBox').put("01", mydepartment);
    }
    return ValueListenableBuilder(
      valueListenable: testBox.listenable(),
      builder: (context, box, widget) {
        return MaterialApp(
          home: SafeArea(
            child: Scaffold(
              appBar: AppBar(
                title: Text("Hive Test"),
              ),
              body: Center(
                  child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  Text("Hive  Sample"),
                  RaisedButton(
                    child: Text("Clear Box"),
                    onPressed: () {
                      Hive.box<Department>('testBox').clear();
                    },
                  ),
                  Text("Person1 Age Now: " + box.get("01").persons[0].age.toString()),
                  RaisedButton(
                    child: Text("Person age UP"),
                    onPressed: () {
                      box.get("01").persons[0].age++;
                      print(box.get("01").persons[0].age);
                    },
                  ),
                  RaisedButton(
                    child: Text("Set State"),
                    onPressed: () {
                      setState(() {});
                    },
                  ),
                  RaisedButton(
                    child: Text("Add person "),
                    onPressed: () {
                      final person2 = new Person(23, "Maria");
                      box.get("01").persons.add(person2);
                    },
                  ),
                  RaisedButton(
                    child: Text("Print person lenght "),
                    onPressed: () {
                      print("Persons: " + Hive.box<Department>('testBox').get("01").persons.length.toString());
                    },
                  )
                ],
              )),
            ),
          ),
        );
      },
    );
  }
}