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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:
A unique id, the name, and the age of each dog.
<code_start>class Dog {
final int id;
final String name;
final int age;
const Dog({
required this.id,
required this.name,
required this.age,
});
}<code_end>
<topic_end>
<topic_start>
3. Open the database
Before reading and writing data to the database, open a connection
to the database. This involves two steps:info Note
In order to use the keyword await, the code must be placed
inside an async function. You should place all the following
table functions inside void main() async {}.
<code_start>// Avoid errors caused by flutter upgrade.
// Importing 'package:flutter/widgets.dart' is required.
WidgetsFlutterBinding.ensureInitialized();
// Open the database and store the reference.
final database = openDatabase(
// Set the path to the database. Note: Using the `join` function from the
// `path` package is best practice to ensure the path is correctly
// constructed for each platform.
join(await getDatabasesPath(), 'doggie_database.db'),
);<code_end>
<topic_end>
<topic_start>
4. Create the dogs table
Next, create a table to store information about various Dogs.
For this example, create a table called dogs that defines the data
that can be stored. Each Dog contains an id, name, and age.
Therefore, these are represented as three columns in the dogs table.For more information about the available Datatypes that can be stored in a
SQLite database, see the official SQLite Datatypes documentation.
<code_start>final database = openDatabase(
// Set the path to the database. Note: Using the `join` function from the
// `path` package is best practice to ensure the path is correctly