Example of using PageStorage to store data during usage of a PageView.

main.dart

import 'package:flutter/material.dart';


void main() => runApp(new MainWidget());


class MainWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        body: new PageView.builder(
          itemBuilder: (context, index) => new MainPageWidget(index),
          itemCount: 3,
        ),
      ),
    );
  }
}


class MainPageWidget extends StatefulWidget {
  final int pageIndex;

  MainPageWidget(this.pageIndex) : super(key: new PageStorageKey<String>('page-$pageIndex'));

  @override
  _MainPageWidgetState createState() => new _MainPageWidgetState();
}

class _MainPageWidgetState extends State<MainPageWidget> {

  static var pageColors = [Colors.red[50], Colors.green[50], Colors.blue[50]];

  final List<TextEditingController> _editController = new List(3);
  Map<String, String> _savedData;


  @override
  void initState() {
    super.initState();
    _savedData = PageStorage.of(context).readState(context, identifier: 'content-${widget.pageIndex}') ?? new Map();
    for (int i = 0; i < _editController.length; i++) {
      _editController[i] = new TextEditingController(text: _savedData['edit$i']);
      _editController[i].addListener(() => _writeState(i, _editController[i].text));
    }
  }

  _writeState(int editIndex, String value) {
    _savedData['edit$editIndex'] = value;
    PageStorage.of(context).writeState(context, _savedData, identifier: 'content-${widget.pageIndex}');
  }

  @override
  Widget build(BuildContext context) {
    return new Container(
      color: pageColors[widget.pageIndex],
      padding: const EdgeInsets.all(24.0),
      child: new Column(
        mainAxisSize: MainAxisSize.max,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          new TextField(controller: _editController[0]),
          new SizedBox(height: 16.0),
          new TextField(controller: _editController[1]),
          new SizedBox(height: 16.0),
          new TextField(controller: _editController[2]),
        ],
      ),
    );
  }
}