How do I get data from an sqflite table and display it as a % inside text widget - flutter

Question

import 'dart:io';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart';
class DatabaseHelper {
static final _databaseName = "MyDatabase.db";
static final _databaseVersion = 1;
static final table = 'my_table';
static final columnId = '_id';
static final columnName = 'name';
static final columnAge = 'age';
// 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 {
Directory documentsDirectory = await getApplicationDocumentsDirectory();
String path = join(documentsDirectory.path, _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,
$columnName TEXT NOT NULL,
$columnAge 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(Map<String, dynamic> row) async {
Database db = await instance.database;
return await db.insert(table, row);
}
// 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);
}
// 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<double> queryRowCount() async {
Database db = await instance.database;
List<Map<String, dynamic>> x = await db.rawQuery('SELECT COUNT(*) FROM $table');
int rowCount = Sqflite.firstIntValue(x);
return rowCount.toDouble();
}
// We are assuming here that the id column in the map is set. The other
// column values will be used to update the row.
Future<int> update(Map<String, dynamic> row) async {
Database db = await instance.database;
int id = row[columnId];
return await db.update(table, row, where: '$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: '$columnId = ?', whereArgs: [id]);
}
Future<List<Map<String, dynamic>>> queryOmnivore() async {
Database db = await instance.database;
return await db.query(table, where: '$columnName = ?', whereArgs: ['omnivore']);
}
Future<List<Map<String, dynamic>>> queryPescatarian() async {
Database db = await instance.database;
return await db.query(table, where: '$columnName = ?', whereArgs: ['pescatarian']);
}
Future<List<Map<String, dynamic>>> queryVegetarian() async {
Database db = await instance.database;
return await db.query(table, where: '$columnName = ?', whereArgs: ['vegetarian']);
}
Future<int> queryVegetarianCount() async {
var vegList = await queryVegetarian();
int count = vegList.length;
return count;
}
Future<double> queryOmnivoreCount() async {
var omniList = await queryOmnivore();
int omniCount = omniList.length;
return omniCount.toDouble();
}
Future<double> calcOmnivorePercentage() async {
var x = await queryOmnivoreCount();
var y = await queryRowCount();
double omniPercentage = (x / y) * 100;
return omniPercentage;
}
}
Hey Folks!
I was hoping someone may be able to help me please?!
I'm trying to figure out how to take data out of a a sqflite table I've created, perform a calculation that expresses it as a percentage of the other values, and display it inside a text widget in the app.
I've actually managed to get the result to print in the console using this code:
void omnivorePercentageQ() async {
final omni = await dbHelper.calcOmnivorePercentage();
print('omnivore percentage: ${omni.toStringAsFixed(1)}');
}
But I have no idea how to get it to show up in a text widget in the app itself.
Any ideas would be greatly appreciated!
Thank you,
Jason

Answer 1

you are not far off the answer, and already catch the value of the calculation needed. As i can see you dont need to pass any parameters to the function so i would recomend using a futurebuilder:
return FutureBuilder(
future: dbHelper.calcOmnivorePercentage(),
builder: (context, AsyncSnapshot<double> snapshot) {
if (snapshot.hasData) {
return Center( child: Text('${snapshot.data.toStringAsFixed(1)}'),);
}else
return Center(
child: CupertinoActivityIndicator(),
);
});
The Future Builder class https://api.flutter.dev/flutter/widgets/FutureBuilder-class.html
Serves to manage widgets that depend on futures, since your calculation and database querys are async you can check its state (As inside the widget in snapshot.hasData). That conditional checks if the future has finished and else shows an indicator. Hope it helps