main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primaryColor: Colors.indigo),
      home: Scaffold(
        backgroundColor: Colors.blueAccent,
        appBar: AppBar(
          title: Text('Counter'),
          centerTitle: true,
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'Tap "-" to decrement',
                style: TextStyle(color: Colors.white),
              ),
              SizedBox(height: 10,),
              CounterWidget(),
              SizedBox(height: 10,),
              Text(
                'Tap "+" to increment',
                style: TextStyle(color: Colors.white),
              )
            ],
          ),
        ),
      ),
    );
  }
}

class CounterWidget extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _CounterWidgetState();
  }
}

class _CounterWidgetState extends State<CounterWidget> {
  int _count = 50;

  @override
  Widget build(BuildContext context) {
    return FittedBox(
      child: Container(
        decoration: BoxDecoration(
            color: Colors.white.withOpacity(0.6),
            borderRadius: BorderRadius.circular(5)),
        child: Row(
          children: <Widget>[
            IconButton(
              icon: const Icon(Icons.remove),
              onPressed: () {
                setState(() {
                  _count--;
                });
              },
            ),
            Text(
              '$_count',
              style: TextStyle(
                fontSize: 20,
              ),
            ),
            IconButton(
              icon: const Icon(Icons.add),
              onPressed: () {
                setState(() {
                  _count++;
                });
              },
            )
          ],
        ),
      ),
    );
  }
}