flutter/examples/api/lib/material/navigation_rail/navigation_rail.extended_animation.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.

// Flutter code sample for NavigationRail.extendedAnimation

import 'dart:ui';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(
        body: MyNavigationRail(),
      ),
    );
  }
}

class MyNavigationRail extends StatefulWidget {
  const MyNavigationRail({Key? key}) : super(key: key);

  @override
  State<MyNavigationRail> createState() => _MyNavigationRailState();
}

class _MyNavigationRailState extends State<MyNavigationRail> {
  int _selectedIndex = 0;
  bool _extended = false;

  @override
  Widget build(BuildContext context) {
    return Row(
      children: <Widget>[
        NavigationRail(
          selectedIndex: _selectedIndex,
          extended: _extended,
          leading: MyNavigationRailFab(onPressed: () {
            setState(() {
              _extended = !_extended;
            });
          }),
          onDestinationSelected: (int index) {
            setState(() {
              _selectedIndex = index;
            });
          },
          labelType: NavigationRailLabelType.none,
          destinations: const <NavigationRailDestination>[
            NavigationRailDestination(
              icon: Icon(Icons.favorite_border),
              selectedIcon: Icon(Icons.favorite),
              label: Text('First'),
            ),
            NavigationRailDestination(
              icon: Icon(Icons.bookmark_border),
              selectedIcon: Icon(Icons.book),
              label: Text('Second'),
            ),
            NavigationRailDestination(
              icon: Icon(Icons.star_border),
              selectedIcon: Icon(Icons.star),
              label: Text('Third'),
            ),
          ],
        ),
        const VerticalDivider(thickness: 1, width: 1),
        // This is the main content.
        Expanded(
          child: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                const Text('Tap on FloatingActionButton to expand'),
                const SizedBox(height: 20),
                Text('selectedIndex: $_selectedIndex'),
              ],
            ),
          ),
        ),
      ],
    );
  }
}

class MyNavigationRailFab extends StatelessWidget {
  const MyNavigationRailFab({Key? key, this.onPressed}) : super(key: key);

  final VoidCallback? onPressed;

  @override
  Widget build(BuildContext context) {
    final Animation<double> animation = NavigationRail.extendedAnimation(context);
    return AnimatedBuilder(
      animation: animation,
      builder: (BuildContext context, Widget? child) {
        // The extended fab has a shorter height than the regular fab.
        return Container(
          height: 56,
          padding: EdgeInsets.symmetric(
            vertical: lerpDouble(0, 6, animation.value)!,
          ),
          child: animation.value == 0
              ? FloatingActionButton(
                  onPressed: onPressed,
                  child: const Icon(Icons.add),
                )
              : Align(
                  alignment: AlignmentDirectional.centerStart,
                  widthFactor: animation.value,
                  child: Padding(
                    padding: const EdgeInsetsDirectional.only(start: 8),
                    child: FloatingActionButton.extended(
                      icon: const Icon(Icons.add),
                      label: const Text('CREATE'),
                      onPressed: onPressed,
                    ),
                  ),
                ),
        );
      },
    );
  }
}