How do I create an animated number counter?

Question

I'd like to create a number counter that animates from a starting value to an end value. I've looked into using a Timer but can't seem to animate/update state properly. Including the decimal value would be great, but a simple integer animation is fine.

Number counter that needs to animate

double _mileCounter = 643.6;

_animateMileCounter() {
  Duration duration = new Duration(milliseconds: 300);
  return new Timer(duration, _updateMileCounter);
}

_updateMileCounter() {
  setState(() {
    _mileCounter += 1;
  });
}

How would I increment the counter X number of times (with animation)? Similar to how a car's odometer increments.

Answer 1

For anyone still looking, you can use ImplicitlyAnimatedWidget.

Here is an example of an int counter. Works analogously for doubles.

class AnimatedCount extends ImplicitlyAnimatedWidget {
  final int count;

  AnimatedCount({
    Key key,
    @required this.count,
    @required Duration duration,
    Curve curve = Curves.linear
  }) : super(duration: duration, curve: curve, key: key);

  @override
  ImplicitlyAnimatedWidgetState<ImplicitlyAnimatedWidget> createState() => _AnimatedCountState();
}

class _AnimatedCountState extends AnimatedWidgetBaseState<AnimatedCount> {
  IntTween _count;

  @override
  Widget build(BuildContext context) {
    return new Text(_count.evaluate(animation).toString());
  }

  @override
  void forEachTween(TweenVisitor visitor) {
    _count = visitor(_count, widget.count, (dynamic value) => new IntTween(begin: value));
  }
}

Just rebuild the widget with a new value and it automatically animates there.

Answer 2

You should use an AnimationController with an AnimatedBuilder to rebuild your text when the controller changes. Here's an example that increments the miles when the floating action button is pressed (double.toStringAsFixed to get the decimal to show), with a curve on the animation speed:

import 'dart:math';
import 'package:flutter/material.dart';

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

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

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);
  @override
  createState() => new MyHomePageState();
}

class MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  AnimationController _controller;
  Animation<double> _animation;
  double _miles = 0.0;

  @override initState() {
    _controller = new AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 1500),
    );
    _animation = _controller;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    TextTheme textTheme = Theme.of(context).textTheme;
    return new Scaffold(
      body: new Material(
        color: const Color.fromRGBO(246, 251, 8, 1.0),
        child: new Center(
          child: new Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              new AnimatedBuilder(
                animation: _animation,
                builder: (BuildContext context, Widget child) {
                  return new Text(
                    _animation.value.toStringAsFixed(1),
                    style: textTheme.display4.copyWith(fontStyle: FontStyle.italic),
                  );
                },
              ),
              new Text(
                  "MILES",
                  style: textTheme.display1.copyWith(fontStyle: FontStyle.italic),
              )
            ],
          ),
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        child: new Icon(Icons.directions_run),
        onPressed: () {
          Random rng = new Random();
          setState(() {
            _miles += rng.nextInt(20) + 0.3;
            _animation = new Tween<double>(
                begin: _animation.value,
                end: _miles,
            ).animate(new CurvedAnimation(
              curve: Curves.fastOutSlowIn,
              parent: _controller,
            ));
          });
          _controller.forward(from: 0.0);
        }
      ),
    );
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }
}

Answer 3

You can use Countup package.

Countup(
  begin: 0,
  end: 7500,
  duration: Duration(seconds: 3),
  separator: ',',
  style: TextStyle(
    fontSize: 36,
  ),
)

https://pub.dev/packages/countup