dev/benchmarks/microbenchmarks/lib/foundation/all_elements_bench.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';
import 'package:flutter/scheduler.dart';
import 'package:flutter/services.dart';
import 'package:flutter_test/flutter_test.dart' show collectAllElementsFrom;

import '../common.dart';

const int _kNumIters = 10000;

Future<void> execute() async {
  runApp(
    MaterialApp(
      home: Scaffold(
        body: GridView.count(
          crossAxisCount: 5,
          children: List<Widget>.generate(25, (int index) {
            return Center(
              child: Scaffold(
                appBar: AppBar(
                  title: Text('App $index'),
                  actions: const <Widget>[Icon(Icons.help), Icon(Icons.add), Icon(Icons.ac_unit)],
                ),
                body: const Column(
                  children: <Widget>[
                    Text('Item 1'),
                    Text('Item 2'),
                    Text('Item 3'),
                    Text('Item 4'),
                  ],
                ),
              ),
            );
          }),
        ),
      ),
    ),
  );

  // Lists may not be scrolled into frame in landscape.
  await SystemChrome.setPreferredOrientations(<DeviceOrientation>[
    DeviceOrientation.portraitUp,
    DeviceOrientation.portraitDown,
  ]);

  // Wait for frame rendering to stabilize.
  for (var i = 0; i < 5; i++) {
    await SchedulerBinding.instance.endOfFrame;
  }

  final watch = Stopwatch();

  print('flutter_test allElements benchmark... (${WidgetsBinding.instance.rootElement})');
  // Make sure we get enough elements to process for consistent benchmark runs
  int elementCount = collectAllElementsFrom(
    WidgetsBinding.instance.rootElement!,
    skipOffstage: false,
  ).length;
  while (elementCount < 2458) {
    await Future<void>.delayed(Duration.zero);
    elementCount = collectAllElementsFrom(
      WidgetsBinding.instance.rootElement!,
      skipOffstage: false,
    ).length;
  }
  print('element count: $elementCount');

  watch.start();
  for (var i = 0; i < _kNumIters; i += 1) {
    final List<Element> allElements = collectAllElementsFrom(
      WidgetsBinding.instance.rootElement!,
      skipOffstage: false,
    ).toList();
    allElements.clear();
  }
  watch.stop();

  final printer = BenchmarkResultPrinter();
  printer.addResult(
    description: 'All elements iterate',
    value: watch.elapsedMicroseconds / _kNumIters,
    unit: 'µs per iteration',
    name: 'all_elements_iteration',
  );
  printer.printToStdout();
}