StatefulWidget Issues

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Example'),
        ),
        body: PageA(),
      ),
    ),
  );
}

class PageA extends StatefulWidget {
  @override
  _PageAState createState() => _PageAState();
}

class _PageAState extends State<PageA> {
  List<String> texts;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        PageB(this.texts),
        RaisedButton(
          child: Text('Get Details'),
          onPressed: () => getDetails(),
        ),
      ],
    );
  }

  Future<void> getDetails() async {
    var texts = await Future.value(['hi']);
    setState(() {
      this.texts = texts;
    });
  }
}

class PageB extends StatefulWidget {
  final List<String> text;

  PageB(this.text);

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

class _PageBState extends State<PageB> {
  @override
  Widget build(BuildContext context) {
    return someAnimation();
  }

  Widget someAnimation() {
    return Container(
      child: Center(
        child: Text(
          'Details: ${widget.text.toString()}',
        ),
      ),
    );
  }
}