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.

// Template: dev/snippets/config/templates/stateful_widget_scaffold_center_freeform_state.tmpl
//
// Comment lines marked with "▼▼▼" and "▲▲▲" are used for authoring
// of samples, and may be ignored if you are just exploring the sample.

// Flutter code sample for SliverAnimatedOpacity
//
//***************************************************************************
//* ▼▼▼▼▼▼▼▼ description ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)

// Creates a [CustomScrollView] with a [SliverFixedExtentList] and a
// [FloatingActionButton]. Pressing the button animates the lists' opacity.

//* ▲▲▲▲▲▲▲▲ description ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
//***************************************************************************

import 'package:flutter/material.dart';

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

/// This is the main application widget.
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

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

/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

/// This is the private State class that goes with MyStatefulWidget.
//********************************************************************
//* ▼▼▼▼▼▼▼▼ code ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)

class _MyStatefulWidgetState extends State<MyStatefulWidget>
    with SingleTickerProviderStateMixin {
  bool _visible = true;

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(slivers: <Widget>[
      SliverAnimatedOpacity(
        opacity: _visible ? 1.0 : 0.0,
        duration: const Duration(milliseconds: 500),
        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),
      )),
    ]);
  }
}

//* ▲▲▲▲▲▲▲▲ code ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
//********************************************************************