content: import 'package:flutter/material.dart';
  import 'package:url_launcher/url_launcher.dart';
  
  class Day64TweenAnimationBuilder extends StatefulWidget {
    Day64TweenAnimationBuilder({Key key}) : super(key: key);
  
    @override
    _Day64TweenAnimationBuilderState createState() =>
        _Day64TweenAnimationBuilderState();
  }
  
  class _Day64TweenAnimationBuilderState
      extends State<Day64TweenAnimationBuilder> {
    bool repeat = true;
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        body: Center(
          // ? What is TweenAnimationBuilder....
          /**
           * ! With the help of TweenAnimationBuilder we can create the custom animation effect to the user....
           */
          child: TweenAnimationBuilder<Color>(
            tween: repeat
                ? ColorTween(begin: Colors.red, end: Colors.green)
                : ColorTween(
                    begin: Colors.green,
                    end: Colors
                        .red), // ! it required the [tween] property to hold the tween value....
            duration: Duration(
                seconds: 3), // ! set the [duration] for the animation timing....
            curve: Curves
                .bounceInOut, // ! set the [curve] for the animation effect....
            builder: (context, value, child) => Container(
              // ! generate the [builder] to display the ui of the animation....
              width: 250,
              height: 250,
              color: value,
            ),
            onEnd: () {
              // ! ues the [onEnd] call back to get the end of the animation....
              print("Tween Animation Ends....");
              setState(() {
                repeat = !repeat;
              });
            },
          ),
        ),
        appBar: AppBar(
          title: Text('TweenAnimationBuilder'),
          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/day064_tween_animation_builder.dart';
                if (await canLaunch(url)) {
                  await launch(url);
                } else {
                  throw 'Could not launch $url';
                }
              },
            )
          ],
        ),
      );
    }
  }
  