// 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 'dart:ui'; import 'package:flutter/scheduler.dart'; import 'package:flutter/services.dart'; import 'package:flutter/widgets.dart'; import 'package:flutter_test/flutter_test.dart'; void main() { test('Instantiating WidgetsFlutterBinding does neither schedule a frame nor register frame callbacks', () async { // Regression test for https://github.com/flutter/flutter/issues/39494. // Preconditions. expect(PlatformDispatcher.instance.onBeginFrame, isNull); expect(PlatformDispatcher.instance.onDrawFrame, isNull); // Instantiation does nothing with regards to frame scheduling. expect(WidgetsFlutterBinding.ensureInitialized(), isA<WidgetsFlutterBinding>()); expect(SchedulerBinding.instance.hasScheduledFrame, isFalse); expect(PlatformDispatcher.instance.onBeginFrame, isNull); expect(PlatformDispatcher.instance.onDrawFrame, isNull); // Framework starts with detached statue. Sends resumed signal to enable frame. final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed')!; await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { }); expect(PlatformDispatcher.instance.onBeginFrame, isNull); expect(PlatformDispatcher.instance.onDrawFrame, isNull); expect(SchedulerBinding.instance.hasScheduledFrame, isFalse); // Frame callbacks are registered lazily (and a frame scheduled) when the root widget is attached. WidgetsBinding.instance.attachRootWidget(const Placeholder()); expect(PlatformDispatcher.instance.onBeginFrame, isNotNull); expect(PlatformDispatcher.instance.onDrawFrame, isNotNull); expect(SchedulerBinding.instance.hasScheduledFrame, isTrue); }); }