samples/animations/lib/src/basics/fade_transition.dart

// Copyright 2019 The Flutter team. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';

// Refer to the AnimatedWidget docs here - https://api.flutter.dev/flutter/widgets/AnimatedWidget-class.html
// for examples of other common animated widgets.
class FadeTransitionDemo extends StatefulWidget {
  const FadeTransitionDemo({super.key});
  static const String routeName = 'basics/fade_transition';

  @override
  State<FadeTransitionDemo> createState() => _FadeTransitionDemoState();
}

class _FadeTransitionDemoState extends State<FadeTransitionDemo>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;
  late final CurvedAnimation _curve;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 500),
    );

    _curve = CurvedAnimation(parent: _controller, curve: Curves.easeIn);

    _animation = Tween(begin: 1.0, end: 0.0).animate(_curve);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Fade Transition')),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            FadeTransition(
              opacity: _animation,
              child: const Icon(Icons.star, color: Colors.amber, size: 300),
            ),
            ElevatedButton(
              child: const Text('animate'),
              onPressed:
                  () => setState(() {
                    _controller
                        .animateTo(1.0)
                        .then<TickerFuture>(
                          (value) => _controller.animateBack(0.0),
                        );
                  }),
            ),
          ],
        ),
      ),
    );
  }
}