animated_label.dart

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Animated Label',
      theme: ThemeData(
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: Home(),
    );
  }
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  double labelValue = 0.0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: Center(
          child: AnimatedLabel(
            labelValue: labelValue,
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.refresh),
        onPressed: () {
          labelValue = math.Random().nextDouble() * 100.0;
          setState(() {});
        },
      ),
    );
  }
}

class AnimatedLabel extends StatelessWidget {
  final double labelValue;
  const AnimatedLabel({
    Key key,
    @required this.labelValue,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TweenAnimationBuilder<double>(
      duration: Duration(milliseconds: 500),
      tween: Tween(begin: 0.0, end: labelValue),
      builder: (context, value, child) {
        return Text(
          '${value.toStringAsFixed(2)}',
          style: TextStyle(fontSize: 50),
        );
      },
    );
  }
}