flutter/examples/api/lib/widgets/transitions/sliver_fade_transition.0.dart

// Copyright 2014 The Flutter Authors. 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';

/// Flutter code sample for [SliverFadeTransition].

void main() => runApp(const SliverFadeTransitionExampleApp());

class SliverFadeTransitionExampleApp extends StatelessWidget {
  const SliverFadeTransitionExampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('SliverFadeTransition Sample')),
        body: const Center(
          child: SliverFadeTransitionExample(),
        ),
      ),
    );
  }
}

class SliverFadeTransitionExample extends StatefulWidget {
  const SliverFadeTransitionExample({super.key});

  @override
  State<SliverFadeTransitionExample> createState() => _SliverFadeTransitionExampleState();
}

class _SliverFadeTransitionExampleState extends State<SliverFadeTransitionExample> with SingleTickerProviderStateMixin {
  late final AnimationController controller = AnimationController(
    duration: const Duration(milliseconds: 1000),
    vsync: this,
  );
  late final Animation<double> animation = CurvedAnimation(
    parent: controller,
    curve: Curves.easeIn,
  );

  @override
  void initState() {
    super.initState();
    animation.addStatusListener((AnimationStatus status) {
      if (status == AnimationStatus.completed) {
        controller.reverse();
      } else if (status == AnimationStatus.dismissed) {
        controller.forward();
      }
    });
    controller.forward();
  }

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

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(slivers: <Widget>[
      SliverFadeTransition(
        opacity: animation,
        sliver: SliverFixedExtentList(
          itemExtent: 100.0,
          delegate: SliverChildBuilderDelegate(
            (BuildContext context, int index) {
              return Container(
                color: index.isEven ? Colors.indigo[200] : Colors.orange[200],
              );
            },
            childCount: 5,
          ),
        ),
      ),
    ]);
  }
}