import 'package:flutter/material.dart';

void main() => runApp(SampleApp());

class SampleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark(),
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      floatingActionButton: FloatingActionButton(
        child: const Icon(Icons.search),
        onPressed: () {
          showSearch(
            context: context,
            delegate: SampleDelegate(),
          );
        },
      ),
      body: const Placeholder(),
    );
  }
}

class SampleDelegate extends SearchDelegate {
  @override
  List<Widget> buildActions(BuildContext context) {
    return <Widget>[
      if (query.isNotEmpty)
        IconButton(
          icon: const Icon(Icons.clear),
          onPressed: () => query = '',
        ),
    ];
  }

  @override
  Widget buildLeading(BuildContext context) => const BackButton();

  @override
  Widget buildResults(BuildContext context) => const Placeholder();

  @override
  Widget buildSuggestions(BuildContext context) => const Placeholder();
}