linear_progress_demo.dart

import 'package:flutter/material.dart';

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

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

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  List nums = [1, 2, 3];

  void _incrementCounter() {
    if (_counter <= 1) {
      setState(() {
        _counter++;
      });
    } else {
      setState(() {
        _counter = 0;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          children: [
            SizedBox(
             width: 100,
             child: LinearProgressIndicator(
               minHeight: 18, 
               backgroundColor: Colors.redAccent, 
               valueColor: AlwaysStoppedAnimation(Colors.red)),
            ),
            Text('${nums[_counter]}'),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        child: Icon(Icons.add),
      ),
    );
  }
}