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Dataset card Data Studio Files
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future<int> readCounter() async {
try {
final file = await _localFile;
// read the file
final contents = await file.readAsString();
return int.parse(contents);
} catch (e) {
// if encountering an error, return 0
return 0;
}
}
Future<File> writeCounter(int counter) async {
final file = await _localFile;
// write the file
return file.writeAsString('$counter');
}
}
class FlutterDemo extends StatefulWidget {
const FlutterDemo({super.key, required this.storage});
final CounterStorage storage;
@override
State<FlutterDemo> createState() => _FlutterDemoState();
}
class _FlutterDemoState extends State<FlutterDemo> {
int _counter = 0;
@override
void initState() {
super.initState();
widget.storage.readCounter().then((value) {
setState(() {
_counter = value;
});
});
}
Future<File> _incrementCounter() {
setState(() {
_counter++;
});
// write the variable as a string to the file.
return widget.storage.writeCounter(_counter);
}
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(
title: const Text('Reading and writing files'),
),
body: center(
child: text(
'button tapped $_counter time${_counter == 1 ? '' : 's'}.',
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'increment',
child: const Icon(Icons.add),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
persist data with SQLite
info note
this guide uses the sqflite package.
this package only supports apps that run on
macOS, iOS, or android.
if you are writing an app that needs to persist and query large amounts of data on
the local device, consider using a database instead of a local file or
key-value store. in general, databases provide faster inserts, updates,
and queries compared to other local persistence solutions.
flutter apps can make use of the SQLite databases via the
sqflite plugin available on pub.dev.
this recipe demonstrates the basics of using sqflite
to insert, read, update, and remove data about various dogs.
if you are new to SQLite and SQL statements, review the
SQLite tutorial to learn the basics before
completing this recipe.
this recipe uses the following steps:
<topic_end>
<topic_start>
1. add the dependencies
to work with SQLite databases, import the sqflite and
path packages.
to add the packages as a dependency,
run flutter pub add:
make sure to import the packages in the file you’ll be working in.
<code_start>
import 'dart:async';
import 'package:flutter/widgets.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
<code_end>
<topic_end>
<topic_start>
2. define the dog data model
before creating the table to store information on dogs, take a few moments to
define the data that needs to be stored. for this example, define a dog class
that contains three pieces of data: