How To Create Bar Charts with charts_flutter

Introduction

The charts_flutter library is a “Material Design data visualization library written natively in Dart”. You can use this library in your Flutter application to display data as bar charts, line charts, scatter plot charts, pie charts, and more.

In this article, you will use data for World of Warcraft subscriber numbers between the years of 2008 to 2015 and display it as a bar chart using charts_flutter.

Prerequisites

To complete this tutorial, you will need:

• To download and install Flutter.
• To download and install Android Studio or Visual Studio Code.
• It is recommended to install plugins for your code editor:
  • Flutter and Dart plugins installed for Android Studio.
  • Flutter extension installed for Visual Studio Code.

This tutorial was verified with Flutter v1.22.2, Android SDK v31.0.2, and Android Studio v4.1.

Step 1 — Setting Up the Project

Once you have your environment set up for Flutter, you can run the following to create a new application:

flutter create charts_flutter_example

Navigate to the new project directory:

cd charts_flutter_example

Using flutter create will produce a demo application that will display the number of times a button is clicked.

Step 2 — Adding the charts_flutter Plugin

Next up, we’ll need to add the charts_flutter plugin within our pubspec.yaml:

dependencies:
  flutter:
    sdk: flutter

  charts_flutter: ^0.10.0

We can now go ahead and run this on the iOS or Android simulator or device of your choice.

Step 3 — Scaffolding the Application

Now, open main.dart in your code editor.

Replace everything in this file with with a MaterialApp that points at a HomePage which can be found at home.dart:

import 'package:flutter/material.dart';
import 'package:charts_flutter_example/home.dart';

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

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

Next, create a new home.dart file and add the following lines of code:

import 'package:flutter/material.dart';

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.red,
        title: Text("World of Warcraft Subscribers"),
      ),
      body: Center(
        child: Text("charts_flutter_example"),
      ),
    );
  }
}

Now that we’ve established a base application, we can go ahead and create the model for our bar chart data.

Step 4 — Building the Subscriber Model

Our bar chart will be focused on showing the amount of World of Warcraft subscribers for a particular year.

Next, create a new subscriber_series.dart file and add the following lines of code:

import 'package:flutter/foundation.dart';
import 'package:charts_flutter/flutter.dart' as charts;

class SubscriberSeries {
  final String year;
  final int subscribers;
  final charts.Color barColor;

  SubscriberSeries(
    {
      @required this.year,
      @required this.subscribers,
      @required this.barColor
    }
  );
}

This allows us to represent our data of year and subscribers.

Step 5 — Creating the Data

For the sake of this tutorial, the data will be created inside of the HomePage as a List<SubscriberSeries>:

Revisit home.dart and add the following lines of code:

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:charts_flutter_example/subscriber_series.dart';

class HomePage extends StatelessWidget {
  final List<SubscriberSeries> data = [
    SubscriberSeries(
      year: "2008",
      subscribers: 10000000,
      barColor: charts.ColorUtil.fromDartColor(Colors.blue),
    ),
    SubscriberSeries(
      year: "2009",
      subscribers: 11000000,
      barColor: charts.ColorUtil.fromDartColor(Colors.blue),
    ),
    SubscriberSeries(
      year: "2010",
      subscribers: 12000000,
      barColor: charts.ColorUtil.fromDartColor(Colors.blue),
    ),
    SubscriberSeries(
      year: "2011",
      subscribers: 10000000,
      barColor: charts.ColorUtil.fromDartColor(Colors.blue),
    ),
    SubscriberSeries(
      year: "2012",
      subscribers: 8500000,
      barColor: charts.ColorUtil.fromDartColor(Colors.blue),
    ),
    SubscriberSeries(
      year: "2013",
      subscribers: 7700000,
      barColor: charts.ColorUtil.fromDartColor(Colors.blue),
    ),
    SubscriberSeries(
      year: "2014",
      subscribers: 7600000,
      barColor: charts.ColorUtil.fromDartColor(Colors.blue),
    ),
    SubscriberSeries(
      year: "2015",
      subscribers: 5500000,
      barColor: charts.ColorUtil.fromDartColor(Colors.red),
    ),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.red,
        title: Text("World of Warcraft Subscribers"),
      ),
      body: Center(
        child: Text("charts_flutter_example"),
      ),
    );
  }
}

Now that we’ve got our data, all we need to is create the bar chart!

Step 6 — Creating the Bar Chart

Now, create a new subscriber_chart.dart file and add the following lines of code:

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:charts_flutter_example/subscriber_series.dart';

class SubscriberChart extends StatelessWidget {
  final List<SubscriberSeries> data;

  SubscriberChart({@required this.data});
}

This code creates a new StatelessWidget named SubscriberChart that takes in the SubscriberSeries as a prop.

We can then use this data to build our charts.Series like so:

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:charts_flutter_example/subscriber_series.dart';

class SubscriberChart extends StatelessWidget {
  final List<SubscriberSeries> data;

  SubscriberChart({@required this.data});

  @override
  Widget build(BuildContext context) {
    List<charts.Series<SubscriberSeries, String>> series = [
      charts.Series(
        id: "Subscribers",
        data: data,
        domainFn: (SubscriberSeries series, _) => series.year,
        measureFn: (SubscriberSeries series, _) => series.subscribers,
        colorFn: (SubscriberSeries series, _) => series.barColor
      )
    ];
  }
}

The domainFn and measureFn are used to compare the subscribers data for that year.

We’re also using the colorFn to potentially pass a barColor.

Recall how home.dart used barColor:

SubscriberSeries(
  year: "2008",
  subscribers: 10000000,
  barColor: charts.ColorUtil.fromDartColor(Colors.blue),
),

We may want to make the barColor optional with a default of Colors.blue (or a color of your choice) in a production application. In this tutorial, one bar will be colored red and the others will be colored blue.

Let’s update the build function to return our chart:

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:charts_flutter_example/subscriber_series.dart';

class SubscriberChart extends StatelessWidget {
  final List<SubscriberSeries> data;

  SubscriberChart({@required this.data});

  @override
  Widget build(BuildContext context) {
    List<charts.Series<SubscriberSeries, String>> series = [
      charts.Series(
        id: "Subscribers",
        data: data,
        domainFn: (SubscriberSeries series, _) => series.year,
        measureFn: (SubscriberSeries series, _) => series.subscribers,
        colorFn: (SubscriberSeries series, _) => series.barColor
      )
    ];

    return Container(
      height: 400,
      padding: EdgeInsets.all(20),
      child: Card(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Column(
            children: <Widget>[
              Text(
                "World of Warcraft Subscribers by Year",
                style: Theme.of(context).textTheme.body2,
              ),
              Expanded(
                child: charts.BarChart(series, animate: true),
              )
            ],
          ),
        ),
      ),
    );
  }
}

This code adds markup to the charts.BarChart by surrounding it with a Card.

The key thing to note is that we’re passing the series as a required parameter to charts.BarChart:

charts.BarChart(series, animate: true)

At this point, your data and chart are ready for use.

Step 7 — Displaying the Chart

Finally, revisit home.dart in your code editor and change the build to use the SubscriberChart:

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:charts_flutter_example/subscriber_series.dart';
import 'package:charts_flutter_example/subscriber_chart.dart';

class HomePage extends StatelessWidget {
  // ...

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.red,
        title: Text("World of Warcraft Subscribers"),
      ),
      body: Center(
        child: SubscriberChart(
          data: data,
        )
      ),
    );
  }
}

Save your changes and run the application in a simulator:

Your application now uses charts_flutter to display data as a bar chart.

Conclusion

In this article, you used data for World of Warcraft subscriber numbers between the years of 2008 to 2015 and displayed it as a bar chart using charts_flutter.

If you’d like to learn more about Flutter, check out our Flutter topic page for exercises and programming projects.