content: import 'package:flutter/cupertino.dart';
  import 'package:flutter/material.dart';
  import 'package:url_launcher/url_launcher.dart';
  
  class Day77CupertinoActivityIndicator extends StatefulWidget {
    const Day77CupertinoActivityIndicator({Key key}) : super(key: key);
  
    @override
    _Day77CupertinoActivityIndicatorState createState() =>
        _Day77CupertinoActivityIndicatorState();
  }
  
  class _Day77CupertinoActivityIndicatorState
      extends State<Day77CupertinoActivityIndicator> {
    bool loader = true;
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        appBar: AppBar(
          title: Text('CupertinoActivityIndicator'),
          actions: <Widget>[
            IconButton(
              icon: Icon(Icons.help),
              onPressed: () async {
                const url =
                    'https://github.com/sanjaysanju618/100-Days-Of-Flutter-Widgets/' +
                        'blob/master/hundred_days_of_flutter_widget/' +
                        'lib/day077_cupertino_activity_indicator.dart';
                if (await canLaunch(url)) {
                  await launch(url);
                } else {
                  throw 'Could not launch $url';
                }
              },
            )
          ],
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: [
              CupertinoActivityIndicator(
                radius: 50,
                animating: loader,
              ),
              RaisedButton(
                color: Theme.of(context).primaryColor,
                onPressed: () {
                  setState(() {
                    loader = !loader;
                  });
                },
                child: Text(
                  loader ? "Stop Loading" : "Start Loading",
                  style: TextStyle(color: Colors.white),
                ),
              )
            ],
          ),
        ),
      );
    }
  }
  