flutter/examples/api/lib/material/app_bar/sliver_app_bar.1.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 [SliverAppBar].

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

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(home: SliverAppBarExample());
  }
}

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

  @override
  State<SliverAppBarExample> createState() => _SliverAppBarExampleState();
}

class _SliverAppBarExampleState extends State<SliverAppBarExample> {
  bool _pinned = true;
  bool _snap = false;
  bool _floating = false;

  // [SliverAppBar]s are typically used in [CustomScrollView.slivers], which in
  // turn can be placed in a [Scaffold.body].
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          SliverAppBar(
            pinned: _pinned,
            snap: _snap,
            floating: _floating,
            expandedHeight: 160.0,
            flexibleSpace: const FlexibleSpaceBar(
              title: Text('SliverAppBar'),
              background: FlutterLogo(),
            ),
          ),
          const SliverToBoxAdapter(
            child: SizedBox(
              height: 20,
              child: Center(child: Text('Scroll to see the SliverAppBar in effect.')),
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate((BuildContext context, int index) {
              return Container(
                color: index.isOdd ? Colors.white : Colors.black12,
                height: 100.0,
                child: Center(child: Text('$index', textScaler: const TextScaler.linear(5))),
              );
            }, childCount: 20),
          ),
        ],
      ),
      bottomNavigationBar: BottomAppBar(
        child: Padding(
          padding: const EdgeInsets.all(8),
          child: OverflowBar(
            overflowAlignment: OverflowBarAlignment.center,
            children: <Widget>[
              Row(
                mainAxisSize: MainAxisSize.min,
                children: <Widget>[
                  const Text('pinned'),
                  Switch(
                    onChanged: (bool val) {
                      setState(() {
                        _pinned = val;
                      });
                    },
                    value: _pinned,
                  ),
                ],
              ),
              Row(
                mainAxisSize: MainAxisSize.min,
                children: <Widget>[
                  const Text('snap'),
                  Switch(
                    onChanged: (bool val) {
                      setState(() {
                        _snap = val;
                        // Snapping only applies when the app bar is floating.
                        _floating = _floating || _snap;
                      });
                    },
                    value: _snap,
                  ),
                ],
              ),
              Row(
                mainAxisSize: MainAxisSize.min,
                children: <Widget>[
                  const Text('floating'),
                  Switch(
                    onChanged: (bool val) {
                      setState(() {
                        _floating = val;
                        _snap = _snap && _floating;
                      });
                    },
                    value: _floating,
                  ),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}