flutter/examples/api/lib/widgets/implicit_animations/sliver_animated_opacity.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 [SliverAnimatedOpacity].

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

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

  static const Duration duration = Duration(milliseconds: 500);
  static const Curve curve = Curves.easeInOut;

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

class SliverAnimatedOpacityExample extends StatefulWidget {
  const SliverAnimatedOpacityExample({
    required this.duration,
    required this.curve,
    super.key,
  });

  final Duration duration;

  final Curve curve;

  @override
  State<SliverAnimatedOpacityExample> createState() =>
      _SliverAnimatedOpacityExampleState();
}

class _SliverAnimatedOpacityExampleState
    extends State<SliverAnimatedOpacityExample>
    with SingleTickerProviderStateMixin {
  bool _visible = true;

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(slivers: <Widget>[
      SliverAnimatedOpacity(
        opacity: _visible ? 1.0 : 0.0,
        duration: widget.duration,
        curve: widget.curve,
        sliver: SliverFixedExtentList(
          itemExtent: 100.0,
          delegate: SliverChildBuilderDelegate(
            (BuildContext context, int index) {
              return Container(
                color: index.isEven ? Colors.indigo[200] : Colors.orange[200],
              );
            },
            childCount: 5,
          ),
        ),
      ),
      SliverToBoxAdapter(
          child: FloatingActionButton(
        onPressed: () {
          setState(() {
            _visible = !_visible;
          });
        },
        tooltip: 'Toggle opacity',
        child: const Icon(Icons.flip),
      )),
    ]);
  }
}