dependencies:
  flutter:
    sdk: flutter
  path_provider: ^2.0.2

import 'package:path_provider/path_provider.dart';
import 'dart:io';

Future<String> get _localPath async {
  final directory = await getApplicationDocumentsDirectory();
  return directory.path;
}

Future<File> get _localFile async {
  final path = await _localPath;
  return File('$path/demo.txt');
}

Future<File> writeContent(String content) async {
  final file = await _localFile;
  return file.writeAsString(content);
}

Future<String> readContent() async {
  try {
    final file = await _localFile;
    String contents = await file.readAsString();
    return contents;
  } catch (e) {
    return 'Error: $e';
  }
}

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: FileStorageDemo(),
    );
  }
}

class FileStorageDemo extends StatefulWidget {
  @override
  _FileStorageDemoState createState() => _FileStorageDemoState();
}

class _FileStorageDemoState extends State<FileStorageDemo> {
  TextEditingController _controller = TextEditingController();
  String _fileContent = '';

  Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();
    return directory.path;
  }

  Future<File> get _localFile async {
    final path = await _localPath;
    return File('$path/demo.txt');
  }

  Future<File> writeContent(String content) async {
    final file = await _localFile;
    return file.writeAsString(content);
  }

  Future<String> readContent() async {
    try {
      final file = await _localFile;
      String contents = await file.readAsString();
      return contents;
    } catch (e) {
      return 'Error: $e';
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Emmagatzematge de Fitxers'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          children: [
            TextField(
              controller: _controller,
              decoration: InputDecoration(labelText: 'Escriu alguna cosa'),
            ),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: () async {
                await writeContent(_controller.text);
                _controller.clear();
              },
              child: Text('Guardar al Fitxer'),
            ),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: () async {
                String content = await readContent();
                setState(() {
                  _fileContent = content;
                });
              },
              child: Text('Llegir del Fitxer'),
            ),
            SizedBox(height: 20),
            Text('Contingut del Fitxer:'),
            Text(_fileContent),
          ],
        ),
      ),
    );
  }
}