flutter sqlite 数据存储

Flutter SQLite Tutorial

In this tutorial, we shall learn basic SQLite operations with the help of a complete Flutter Application.

Use Case

We maintain a car database where each car has an id, name and number of miles driven. Our Application should be able to insert a row into the database, query rows, update a row or delete a row based on the required fields provided.

About UI

Following example application contains a TabBar with TabBarView for operations Insert, View, Query, Update and Delete operations that we shall perform on the car_table.

In Insert Screen, we shall take car name and number of miles it has gone through TextField widgets. Then when you click on the Insert button, we shall prepare the Car object through _insert() method of main() and call insert() method of Database Helper.

In View Screen, there a Refresh button. When you click on it, it queries all the rows and displays them in a ListView.

In Query Screen, there is a TextField to get the name of the car from user. We have attached onChanged() method, so that, when user starts typing, it dynamically queries the table and shows the rows below the button in a ListView.

In Update Screen, we have three TextFields for reading id, name and miles from user. When user enters these fields and click update button, we shall update name and miles for the id provided. You can go the View tab, press on Refresh button to see if the update happened.

In Delete Screen, we have a TextField to read id. When user provides the id and presses Delete button, the row shall be deleted, based on id, if present in the database table.

Dependencies

Under dependencies section, below flutter property, add sqlite and path packages.

dependencies:
  flutter:
    sdk: flutter
  sqflite:
  path:

And click on Packages get button on the top right corner of editor.

No need to mention the version number for the packages sqflite and path.

Class File

Under lib folder, create a file named car.dart with class as shown below.

car.dart

import 'package:flutter_sqlite_tutorial/dbhelper.dart';


class Car {
  int id;
  String name;
  int miles;


  Car(this.id, this.name, this.miles);


  Car.fromMap(Map<String, dynamic> map) {
    id = map['id'];
    name = map['name'];
    miles = map['miles'];
  }


  Map<String, dynamic> toMap() {
    return {
      DatabaseHelper.columnId: id,
      DatabaseHelper.columnName: name,
      DatabaseHelper.columnMiles: miles,
    };
  }
}

We shall use this class type to transfer data between UI (main.dart) and Database Helper Class.

Database Helper Class

Create a Database helper Class as shown below.

It contains methods to create a Database if not present, connect to the database, perform SQLite operations like query rows from table, update a row, delete a row, insert a row, etc.

dbhelper.dart

import 'package:flutter_sqlite_tutorial/car.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';


class DatabaseHelper {


  static final _databaseName = "cardb.db";
  static final _databaseVersion = 1;


  static final table = 'cars_table';


  static final columnId = 'id';
  static final columnName = 'name';
  static final columnMiles = 'miles';


  // make this a singleton class
  DatabaseHelper._privateConstructor();
  static final DatabaseHelper instance = DatabaseHelper._privateConstructor();


  // only have a single app-wide reference to the database
  static Database _database;
  Future<Database> get database async {
    if (_database != null) return _database;
    // lazily instantiate the db the first time it is accessed
    _database = await _initDatabase();
    return _database;
  }


  // this opens the database (and creates it if it doesn't exist)
  _initDatabase() async {
    String path = join(await getDatabasesPath(), _databaseName);
    return await openDatabase(path,
        version: _databaseVersion,
        onCreate: _onCreate);
  }


  // SQL code to create the database table
  Future _onCreate(Database db, int version) async {
    await db.execute('''
          CREATE TABLE $table (
            $columnId INTEGER PRIMARY KEY AUTOINCREMENT,
            $columnName TEXT NOT NULL,
            $columnMiles INTEGER NOT NULL
          )
          ''');
  }


  // Helper methods


  // Inserts a row in the database where each key in the Map is a column name
  // and the value is the column value. The return value is the id of the
  // inserted row.
  Future<int> insert(Car car) async {
    Database db = await instance.database;
    return await db.insert(table, {'name': car.name, 'miles': car.miles});
  }


  // All of the rows are returned as a list of maps, where each map is
  // a key-value list of columns.
  Future<List<Map<String, dynamic>>> queryAllRows() async {
    Database db = await instance.database;
    return await db.query(table);
  }
   
  // Queries rows based on the argument received
  Future<List<Map<String, dynamic>>> queryRows(name) async {
    Database db = await instance.database;
    return await db.query(table, where: "$columnName LIKE '%$name%'");
  }


  // All of the methods (insert, query, update, delete) can also be done using
  // raw SQL commands. This method uses a raw query to give the row count.
  Future<int> queryRowCount() async {
    Database db = await instance.database;
    return Sqflite.firstIntValue(await db.rawQuery('SELECT COUNT(*) FROM $table'));
  }


  // We are assuming here that the id column in the map is set. The other
  // column values will be used to update the row.
  Future<int> update(Car car) async {
    Database db = await instance.database;
    int id = car.toMap()['id'];
    return await db.update(table, car.toMap(), where: '$columnId = ?', whereArgs: [id]);
  }


  // Deletes the row specified by the id. The number of affected rows is
  // returned. This should be 1 as long as the row exists.
  Future<int> delete(int id) async {
    Database db = await instance.database;
    return await db.delete(table, where: '$columnId = ?', whereArgs: [id]);
  }
}

Observe that we have imported the sqflite and path at the start of our main.dart file.

Flutter UI

Following is the complete main.dart file.

main.dart

import 'package:flutter/material.dart';
import 'package:flutter_sqlite_tutorial/car.dart';
import 'package:flutter_sqlite_tutorial/dbhelper.dart';


void main() => runApp(MyApp());


class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'TutorialKart - Flutter',
      theme: ThemeData(
        primarySwatch: Colors.purple,
      ),
      home: MyHomePage(),
    );
  }
}


class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}


class _MyHomePageState extends State<MyHomePage> {
  final dbHelper = DatabaseHelper.instance;


  List<Car> cars = [];
  List<Car> carsByName = [];


  //controllers used in insert operation UI
  TextEditingController nameController = TextEditingController();
  TextEditingController milesController = TextEditingController();


  //controllers used in update operation UI
  TextEditingController idUpdateController = TextEditingController();
  TextEditingController nameUpdateController = TextEditingController();
  TextEditingController milesUpdateController = TextEditingController();


  //controllers used in delete operation UI
  TextEditingController idDeleteController = TextEditingController();


  //controllers used in query operation UI
  TextEditingController queryController = TextEditingController();


  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();


  void _showMessageInScaffold(String message){
    _scaffoldKey.currentState.showSnackBar(
        SnackBar(
          content: Text(message),
        )
    );
  }


  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: 5,
      child: Scaffold(
        key: _scaffoldKey,
        appBar: AppBar(
          bottom: TabBar(
            tabs: [
              Tab(
                text: "Insert",
              ),
              Tab(
                text: "View",
              ),
              Tab(
                text: "Query",
              ),
              Tab(
                text: "Update",
              ),
              Tab(
                text: "Delete",
              ),
            ],
          ),
          title: Text('TutorialKart - Flutter SQLite Tutorial'),
        ),
        body: TabBarView(
          children: [
            Center(
              child: Column(
                children: <Widget>[
                  Container(
                    padding: EdgeInsets.all(20),
                    child: TextField(
                      controller: nameController,
                      decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'Car Name',
                      ),
                    ),
                  ),
                  Container(
                    padding: EdgeInsets.all(20),
                    child: TextField(
                      controller: milesController,
                      decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'Car Miles',
                      ),
                    ),
                  ),
                  RaisedButton(
                    child: Text('Insert Car Details'),
                    onPressed: () {
                      String name = nameController.text;
                      int miles = int.parse(milesController.text);
                      _insert(name, miles);
                    },
                  ),
                ],
              ),
            ),
            Container(
              child: ListView.builder(
                padding: const EdgeInsets.all(8),
                itemCount: cars.length + 1,
                itemBuilder: (BuildContext context, int index) {
                  if (index == cars.length) {
                    return RaisedButton(
                      child: Text('Refresh'),
                      onPressed: () {
                        setState(() {
                          _queryAll();
                        });
                      },
                    );
                  }
                  return Container(
                    height: 40,
                    child: Center(
                      child: Text(
                        '[${cars[index].id}] ${cars[index].name} - ${cars[index].miles} miles',
                        style: TextStyle(fontSize: 18),
                      ),
                    ),
                  );
                },
              ),
            ),
            Center(
              child: Column(
                children: <Widget>[
                  Container(
                    padding: EdgeInsets.all(20),
                    child: TextField(
                      controller: queryController,
                      decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'Car Name',
                      ),
                      onChanged: (text) {
                        if (text.length >= 2) {
                          setState(() {
                            _query(text);
                          });
                        } else {
                          setState(() {
                            carsByName.clear();
                          });
                        }
                      },
                    ),
                    height: 100,
                  ),
                  Container(
                    height: 300,
                    child: ListView.builder(
                      padding: const EdgeInsets.all(8),
                      itemCount: carsByName.length,
                      itemBuilder: (BuildContext context, int index) {
                        return Container(
                          height: 50,
                          margin: EdgeInsets.all(2),
                          child: Center(
                            child: Text(
                              '[${carsByName[index].id}] ${carsByName[index].name} - ${carsByName[index].miles} miles',
                              style: TextStyle(fontSize: 18),
                            ),
                          ),
                        );
                      },
                    ),
                  ),
                ],
              ),
            ),
            Center(
              child: Column(
                children: <Widget>[
                  Container(
                    padding: EdgeInsets.all(20),
                    child: TextField(
                      controller: idUpdateController,
                      decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'Car id',
                      ),
                    ),
                  ),
                  Container(
                    padding: EdgeInsets.all(20),
                    child: TextField(
                      controller: nameUpdateController,
                      decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'Car Name',
                      ),
                    ),
                  ),
                  Container(
                    padding: EdgeInsets.all(20),
                    child: TextField(
                      controller: milesUpdateController,
                      decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'Car Miles',
                      ),
                    ),
                  ),
                  RaisedButton(
                    child: Text('Update Car Details'),
                    onPressed: () {
                      int id = int.parse(idUpdateController.text);
                      String name = nameUpdateController.text;
                      int miles = int.parse(milesUpdateController.text);
                      _update(id, name, miles);
                    },
                  ),
                ],
              ),
            ),
            Center(
              child: Column(
                children: <Widget>[
                  Container(
                    padding: EdgeInsets.all(20),
                    child: TextField(
                      controller: idDeleteController,
                      decoration: InputDecoration(
                        border: OutlineInputBorder(),
                        labelText: 'Car id',
                      ),
                    ),
                  ),
                  RaisedButton(
                    child: Text('Delete'),
                    onPressed: () {
                      int id = int.parse(idDeleteController.text);
                      _delete(id);
                    },
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }


  void _insert(name, miles) async {
    // row to insert
    Map<String, dynamic> row = {
      DatabaseHelper.columnName: name,
      DatabaseHelper.columnMiles: miles
    };
    Car car = Car.fromMap(row);
    final id = await dbHelper.insert(car);
    _showMessageInScaffold('inserted row id: $id');
  }


  void _queryAll() async {
    final allRows = await dbHelper.queryAllRows();
    cars.clear();
    allRows.forEach((row) => cars.add(Car.fromMap(row)));
    _showMessageInScaffold('Query done.');
    setState(() {});
  }


  void _query(name) async {
    final allRows = await dbHelper.queryRows(name);
    carsByName.clear();
    allRows.forEach((row) => carsByName.add(Car.fromMap(row)));
  }


  void _update(id, name, miles) async {
    // row to update
    Car car = Car(id, name, miles);
    final rowsAffected = await dbHelper.update(car);
    _showMessageInScaffold('updated $rowsAffected row(s)');
  }


  void _delete(id) async {
    // Assuming that the number of rows is the id for the last row.
    final rowsDeleted = await dbHelper.delete(id);
    _showMessageInScaffold('deleted $rowsDeleted row(s): row $id');
  }
}

 

分类: 默认 标签: 发布于: 2022-06-16 10:10:23, 更新于: 2022-06-16 17:26:03