packages/flutter/lib/src/services/binding.dart - external/github.com/flutter/flutter - Git at Google

 // 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:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:ui' as ui;

 import 'package:flutter/foundation.dart';
 import 'package:flutter/scheduler.dart';

 import 'asset_bundle.dart';
 import 'binary_messenger.dart';
 import 'hardware_keyboard.dart';
 import 'message_codec.dart';
 import 'restoration.dart';
 import 'system_channels.dart';
 import 'text_input.dart';

 export 'dart:ui' show ChannelBuffers;

 export 'binary_messenger.dart' show BinaryMessenger;
 export 'hardware_keyboard.dart' show HardwareKeyboard, KeyEventManager;
 export 'restoration.dart' show RestorationManager;

 /// Listens for platform messages and directs them to the [defaultBinaryMessenger].
 ///
 /// The [ServicesBinding] also registers a [LicenseEntryCollector] that exposes
 /// the licenses found in the `LICENSE` file stored at the root of the asset
 /// bundle, and implements the `ext.flutter.evict` service extension (see
 /// [evict]).
 mixin ServicesBinding on BindingBase, SchedulerBinding {
   @override
   void initInstances() {
     super.initInstances();
     _instance = this;
     _defaultBinaryMessenger = createBinaryMessenger();
     _restorationManager = createRestorationManager();
     _initKeyboard();
     initLicenses();
     SystemChannels.system.setMessageHandler((dynamic message) => handleSystemMessage(message as Object));
     SystemChannels.lifecycle.setMessageHandler(_handleLifecycleMessage);
     SystemChannels.platform.setMethodCallHandler(_handlePlatformMessage);
     TextInput.ensureInitialized();
     readInitialLifecycleStateFromNativeWindow();
   }

   /// The current [ServicesBinding], if one has been created.
   ///
   /// Provides access to the features exposed by this mixin. The binding must
   /// be initialized before using this getter; this is typically done by calling
   /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
   static ServicesBinding get instance => BindingBase.checkInstance(_instance);
   static ServicesBinding? _instance;

   /// The global singleton instance of [HardwareKeyboard], which can be used to
   /// query keyboard states.
   HardwareKeyboard get keyboard => _keyboard;
   late final HardwareKeyboard _keyboard;

   /// The global singleton instance of [KeyEventManager], which is used
   /// internally to dispatch key messages.
   KeyEventManager get keyEventManager => _keyEventManager;
   late final KeyEventManager _keyEventManager;

   void _initKeyboard() {
     _keyboard = HardwareKeyboard();
     _keyEventManager = KeyEventManager(_keyboard, RawKeyboard.instance);
     platformDispatcher.onKeyData = _keyEventManager.handleKeyData;
     SystemChannels.keyEvent.setMessageHandler(_keyEventManager.handleRawKeyMessage);
   }

   /// The default instance of [BinaryMessenger].
   ///
   /// This is used to send messages from the application to the platform, and
   /// keeps track of which handlers have been registered on each channel so
   /// it may dispatch incoming messages to the registered handler.
   ///
   /// The default implementation returns a [BinaryMessenger] that delivers the
   /// messages in the same order in which they are sent.
   BinaryMessenger get defaultBinaryMessenger => _defaultBinaryMessenger;
   late final BinaryMessenger _defaultBinaryMessenger;

   /// The low level buffering and dispatch mechanism for messages sent by
   /// plugins on the engine side to their corresponding plugin code on
   /// the framework side.
   ///
   /// This exposes the [dart:ui.channelBuffers] object. Bindings can override
   /// this getter to intercept calls to the [ChannelBuffers] mechanism (for
   /// example, for tests).
   ///
   /// In production, direct access to this object should not be necessary.
   /// Messages are received and dispatched by the [defaultBinaryMessenger]. This
   /// object is primarily used to send mock messages in tests, via the
   /// [ChannelBuffers.push] method (simulating a plugin sending a message to the
   /// framework).
   ///
   /// See also:
   ///
   ///  * [PlatformDispatcher.sendPlatformMessage], which is used for sending
   ///    messages to plugins from the framework (the opposite of
   ///    [channelBuffers]).
   ///  * [platformDispatcher], the [PlatformDispatcher] singleton.
   ui.ChannelBuffers get channelBuffers => ui.channelBuffers;

   /// Creates a default [BinaryMessenger] instance that can be used for sending
   /// platform messages.
   ///
   /// Many Flutter framework components that communicate with the platform
   /// assume messages are received by the platform in the same order in which
   /// they are sent. When overriding this method, be sure the [BinaryMessenger]
   /// implementation guarantees FIFO delivery.
   @protected
   BinaryMessenger createBinaryMessenger() {
     return const _DefaultBinaryMessenger._();
   }

   /// Called when the operating system notifies the application of a memory
   /// pressure situation.
   ///
   /// This method exposes the `memoryPressure` notification from
   /// [SystemChannels.system].
   @protected
   @mustCallSuper
   void handleMemoryPressure() {
     rootBundle.clear();
   }

   /// Handler called for messages received on the [SystemChannels.system]
   /// message channel.
   ///
   /// Other bindings may override this to respond to incoming system messages.
   @protected
   @mustCallSuper
   Future<void> handleSystemMessage(Object systemMessage) async {
     final Map<String, dynamic> message = systemMessage as Map<String, dynamic>;
     final String type = message['type'] as String;
     switch (type) {
       case 'memoryPressure':
         handleMemoryPressure();
         break;
     }
     return;
   }

   /// Adds relevant licenses to the [LicenseRegistry].
   ///
   /// By default, the [ServicesBinding]'s implementation of [initLicenses] adds
   /// all the licenses collected by the `flutter` tool during compilation.
   @protected
   @mustCallSuper
   void initLicenses() {
     LicenseRegistry.addLicense(_addLicenses);
   }

   Stream<LicenseEntry> _addLicenses() {
     late final StreamController<LicenseEntry> controller;
     controller = StreamController<LicenseEntry>(
       onListen: () async {
         late final String rawLicenses;
         if (kIsWeb) {
           // NOTICES for web isn't compressed since we don't have access to
           // dart:io on the client side and it's already compressed between
           // the server and client.
           rawLicenses = await rootBundle.loadString('NOTICES', cache: false);
         } else {
           // The compressed version doesn't have a more common .gz extension
           // because gradle for Android non-transparently manipulates .gz files.
           final ByteData licenseBytes = await rootBundle.load('NOTICES.Z');
           final List<int> unzippedBytes = await compute<List<int>, List<int>>(gzip.decode, licenseBytes.buffer.asUint8List(), debugLabel: 'decompressLicenses');
           rawLicenses = await compute<List<int>, String>(utf8.decode, unzippedBytes, debugLabel: 'utf8DecodeLicenses');
         }
         final List<LicenseEntry> licenses = await compute<String, List<LicenseEntry>>(_parseLicenses, rawLicenses, debugLabel: 'parseLicenses');
         licenses.forEach(controller.add);
         await controller.close();
       },
     );
     return controller.stream;
   }

   // This is run in another isolate created by _addLicenses above.
   static List<LicenseEntry> _parseLicenses(String rawLicenses) {
     final String licenseSeparator = '\n${'-' * 80}\n';
     final List<LicenseEntry> result = <LicenseEntry>[];
     final List<String> licenses = rawLicenses.split(licenseSeparator);
     for (final String license in licenses) {
       final int split = license.indexOf('\n\n');
       if (split >= 0) {
         result.add(LicenseEntryWithLineBreaks(
           license.substring(0, split).split('\n'),
           license.substring(split + 2),
         ));
       } else {
         result.add(LicenseEntryWithLineBreaks(const <String>[], license));
       }
     }
     return result;
   }

   @override
   void initServiceExtensions() {
     super.initServiceExtensions();

     assert(() {
       registerStringServiceExtension(
         // ext.flutter.evict value=foo.png will cause foo.png to be evicted from
         // the rootBundle cache and cause the entire image cache to be cleared.
         // This is used by hot reload mode to clear out the cache of resources
         // that have changed.
         name: 'evict',
         getter: () async => '',
         setter: (String value) async {
           evict(value);
         },
       );
       return true;
     }());
   }

   /// Called in response to the `ext.flutter.evict` service extension.
   ///
   /// This is used by the `flutter` tool during hot reload so that any images
   /// that have changed on disk get cleared from caches.
   @protected
   @mustCallSuper
   void evict(String asset) {
     rootBundle.evict(asset);
   }

   // App life cycle

   /// Initializes the [lifecycleState] with the
   /// [dart:ui.PlatformDispatcher.initialLifecycleState].
   ///
   /// Once the [lifecycleState] is populated through any means (including this
   /// method), this method will do nothing. This is because the
   /// [dart:ui.PlatformDispatcher.initialLifecycleState] may already be
   /// stale and it no longer makes sense to use the initial state at dart vm
   /// startup as the current state anymore.
   ///
   /// The latest state should be obtained by subscribing to
   /// [WidgetsBindingObserver.didChangeAppLifecycleState].
   @protected
   void readInitialLifecycleStateFromNativeWindow() {
     if (lifecycleState != null) {
       return;
     }
     final AppLifecycleState? state = _parseAppLifecycleMessage(platformDispatcher.initialLifecycleState);
     if (state != null) {
       handleAppLifecycleStateChanged(state);
     }
   }

   Future<String?> _handleLifecycleMessage(String? message) async {
     handleAppLifecycleStateChanged(_parseAppLifecycleMessage(message!)!);
     return null;
   }

   Future<void> _handlePlatformMessage(MethodCall methodCall) async {
     final String method = methodCall.method;
     // There is only one incoming method call currently possible.
     assert(method == 'SystemChrome.systemUIChange');
     final List<dynamic> args = methodCall.arguments as List<dynamic>;
     if (_systemUiChangeCallback != null) {
       await _systemUiChangeCallback!(args[0] as bool);
     }
   }

   static AppLifecycleState? _parseAppLifecycleMessage(String message) {
     switch (message) {
       case 'AppLifecycleState.paused':
         return AppLifecycleState.paused;
       case 'AppLifecycleState.resumed':
         return AppLifecycleState.resumed;
       case 'AppLifecycleState.inactive':
         return AppLifecycleState.inactive;
       case 'AppLifecycleState.detached':
         return AppLifecycleState.detached;
     }
     return null;
   }

   /// The [RestorationManager] synchronizes the restoration data between
   /// engine and framework.
   ///
   /// See the docs for [RestorationManager] for a discussion of restoration
   /// state and how it is organized in Flutter.
   ///
   /// To use a different [RestorationManager] subclasses can override
   /// [createRestorationManager], which is called to create the instance
   /// returned by this getter.
   RestorationManager get restorationManager => _restorationManager;
   late RestorationManager _restorationManager;

   /// Creates the [RestorationManager] instance available via
   /// [restorationManager].
   ///
   /// Can be overridden in subclasses to create a different [RestorationManager].
   @protected
   RestorationManager createRestorationManager() {
     return RestorationManager();
   }

   SystemUiChangeCallback? _systemUiChangeCallback;

   /// Sets the callback for the `SystemChrome.systemUIChange` method call
   /// received on the [SystemChannels.platform] channel.
   ///
   /// This is typically not called directly. System UI changes that this method
   /// responds to are associated with [SystemUiMode]s, which are configured
   /// using [SystemChrome]. Use [SystemChrome.setSystemUIChangeCallback] to configure
   /// along with other SystemChrome settings.
   ///
   /// See also:
   ///
   ///   * [SystemChrome.setEnabledSystemUIMode], which specifies the
   ///     [SystemUiMode] to have visible when the application is running.
   // ignore: use_setters_to_change_properties, (API predates enforcing the lint)
   void setSystemUiChangeCallback(SystemUiChangeCallback? callback) {
     _systemUiChangeCallback = callback;
   }

 }

 /// Signature for listening to changes in the [SystemUiMode].
 ///
 /// Set by [SystemChrome.setSystemUIChangeCallback].
 typedef SystemUiChangeCallback = Future<void> Function(bool systemOverlaysAreVisible);

 /// The default implementation of [BinaryMessenger].
 ///
 /// This messenger sends messages from the app-side to the platform-side and
 /// dispatches incoming messages from the platform-side to the appropriate
 /// handler.
 class _DefaultBinaryMessenger extends BinaryMessenger {
   const _DefaultBinaryMessenger._();

   @override
   Future<void> handlePlatformMessage(
     String channel,
     ByteData? message,
     ui.PlatformMessageResponseCallback? callback,
   ) async {
     ui.channelBuffers.push(channel, message, (ByteData? data) {
       if (callback != null) {
         callback(data);
       }
     });
   }

   @override
   Future<ByteData?> send(String channel, ByteData? message) {
     final Completer<ByteData?> completer = Completer<ByteData?>();
     // ui.PlatformDispatcher.instance is accessed directly instead of using
     // ServicesBinding.instance.platformDispatcher because this method might be
     // invoked before any binding is initialized. This issue was reported in
     // #27541. It is not ideal to statically access
     // ui.PlatformDispatcher.instance because the PlatformDispatcher may be
     // dependency injected elsewhere with a different instance. However, static
     // access at this location seems to be the least bad option.
     // TODO(ianh): Use ServicesBinding.instance once we have better diagnostics
     // on that getter.
     ui.PlatformDispatcher.instance.sendPlatformMessage(channel, message, (ByteData? reply) {
       try {
         completer.complete(reply);
       } catch (exception, stack) {
         FlutterError.reportError(FlutterErrorDetails(
           exception: exception,
           stack: stack,
           library: 'services library',
           context: ErrorDescription('during a platform message response callback'),
         ));
       }
     });
     return completer.future;
   }

   @override
   void setMessageHandler(String channel, MessageHandler? handler) {
     if (handler == null) {
       ui.channelBuffers.clearListener(channel);
     } else {
       ui.channelBuffers.setListener(channel, (ByteData? data, ui.PlatformMessageResponseCallback callback) async {
         ByteData? response;
         try {
           response = await handler(data);
         } catch (exception, stack) {
           FlutterError.reportError(FlutterErrorDetails(
             exception: exception,
             stack: stack,
             library: 'services library',
             context: ErrorDescription('during a platform message callback'),
           ));
         } finally {
           callback(response);
         }
       });
     }
   }
 }
	// 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:async';
	import 'dart:convert';
	import 'dart:io';
	import 'dart:ui' as ui;

	import 'package:flutter/foundation.dart';
	import 'package:flutter/scheduler.dart';

	import 'asset_bundle.dart';
	import 'binary_messenger.dart';
	import 'hardware_keyboard.dart';
	import 'message_codec.dart';
	import 'restoration.dart';
	import 'system_channels.dart';
	import 'text_input.dart';

	export 'dart:ui' show ChannelBuffers;

	export 'binary_messenger.dart' show BinaryMessenger;
	export 'hardware_keyboard.dart' show HardwareKeyboard, KeyEventManager;
	export 'restoration.dart' show RestorationManager;

	/// Listens for platform messages and directs them to the [defaultBinaryMessenger].
	///
	/// The [ServicesBinding] also registers a [LicenseEntryCollector] that exposes
	/// the licenses found in the `LICENSE` file stored at the root of the asset
	/// bundle, and implements the `ext.flutter.evict` service extension (see
	/// [evict]).
	mixin ServicesBinding on BindingBase, SchedulerBinding {
	@override
	void initInstances() {
	super.initInstances();
	_instance = this;
	_defaultBinaryMessenger = createBinaryMessenger();
	_restorationManager = createRestorationManager();
	_initKeyboard();
	initLicenses();
	SystemChannels.system.setMessageHandler((dynamic message) => handleSystemMessage(message as Object));
	SystemChannels.lifecycle.setMessageHandler(_handleLifecycleMessage);
	SystemChannels.platform.setMethodCallHandler(_handlePlatformMessage);
	TextInput.ensureInitialized();
	readInitialLifecycleStateFromNativeWindow();
	}

	/// The current [ServicesBinding], if one has been created.
	///
	/// Provides access to the features exposed by this mixin. The binding must
	/// be initialized before using this getter; this is typically done by calling
	/// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
	static ServicesBinding get instance => BindingBase.checkInstance(_instance);
	static ServicesBinding? _instance;

	/// The global singleton instance of [HardwareKeyboard], which can be used to
	/// query keyboard states.
	HardwareKeyboard get keyboard => _keyboard;
	late final HardwareKeyboard _keyboard;

	/// The global singleton instance of [KeyEventManager], which is used
	/// internally to dispatch key messages.
	KeyEventManager get keyEventManager => _keyEventManager;
	late final KeyEventManager _keyEventManager;

	void _initKeyboard() {
	_keyboard = HardwareKeyboard();
	_keyEventManager = KeyEventManager(_keyboard, RawKeyboard.instance);
	platformDispatcher.onKeyData = _keyEventManager.handleKeyData;
	SystemChannels.keyEvent.setMessageHandler(_keyEventManager.handleRawKeyMessage);
	}

	/// The default instance of [BinaryMessenger].
	///
	/// This is used to send messages from the application to the platform, and
	/// keeps track of which handlers have been registered on each channel so
	/// it may dispatch incoming messages to the registered handler.
	///
	/// The default implementation returns a [BinaryMessenger] that delivers the
	/// messages in the same order in which they are sent.
	BinaryMessenger get defaultBinaryMessenger => _defaultBinaryMessenger;
	late final BinaryMessenger _defaultBinaryMessenger;

	/// The low level buffering and dispatch mechanism for messages sent by
	/// plugins on the engine side to their corresponding plugin code on
	/// the framework side.
	///
	/// This exposes the [dart:ui.channelBuffers] object. Bindings can override
	/// this getter to intercept calls to the [ChannelBuffers] mechanism (for
	/// example, for tests).
	///
	/// In production, direct access to this object should not be necessary.
	/// Messages are received and dispatched by the [defaultBinaryMessenger]. This
	/// object is primarily used to send mock messages in tests, via the
	/// [ChannelBuffers.push] method (simulating a plugin sending a message to the
	/// framework).
	///
	/// See also:
	///
	/// * [PlatformDispatcher.sendPlatformMessage], which is used for sending
	/// messages to plugins from the framework (the opposite of
	/// [channelBuffers]).
	/// * [platformDispatcher], the [PlatformDispatcher] singleton.
	ui.ChannelBuffers get channelBuffers => ui.channelBuffers;

	/// Creates a default [BinaryMessenger] instance that can be used for sending
	/// platform messages.
	///
	/// Many Flutter framework components that communicate with the platform
	/// assume messages are received by the platform in the same order in which
	/// they are sent. When overriding this method, be sure the [BinaryMessenger]
	/// implementation guarantees FIFO delivery.
	@protected
	BinaryMessenger createBinaryMessenger() {
	return const _DefaultBinaryMessenger._();
	}

	/// Called when the operating system notifies the application of a memory
	/// pressure situation.
	///
	/// This method exposes the `memoryPressure` notification from
	/// [SystemChannels.system].
	@protected
	@mustCallSuper
	void handleMemoryPressure() {
	rootBundle.clear();
	}

	/// Handler called for messages received on the [SystemChannels.system]
	/// message channel.
	///
	/// Other bindings may override this to respond to incoming system messages.
	@protected
	@mustCallSuper
	Future<void> handleSystemMessage(Object systemMessage) async {
	final Map<String, dynamic> message = systemMessage as Map<String, dynamic>;
	final String type = message['type'] as String;
	switch (type) {
	case 'memoryPressure':
	handleMemoryPressure();
	break;
	}
	return;
	}

	/// Adds relevant licenses to the [LicenseRegistry].
	///
	/// By default, the [ServicesBinding]'s implementation of [initLicenses] adds
	/// all the licenses collected by the `flutter` tool during compilation.
	@protected
	@mustCallSuper
	void initLicenses() {
	LicenseRegistry.addLicense(_addLicenses);
	}

	Stream<LicenseEntry> _addLicenses() {
	late final StreamController<LicenseEntry> controller;
	controller = StreamController<LicenseEntry>(
	onListen: () async {
	late final String rawLicenses;
	if (kIsWeb) {
	// NOTICES for web isn't compressed since we don't have access to
	// dart:io on the client side and it's already compressed between
	// the server and client.
	rawLicenses = await rootBundle.loadString('NOTICES', cache: false);
	} else {
	// The compressed version doesn't have a more common .gz extension
	// because gradle for Android non-transparently manipulates .gz files.
	final ByteData licenseBytes = await rootBundle.load('NOTICES.Z');
	final List<int> unzippedBytes = await compute<List<int>, List<int>>(gzip.decode, licenseBytes.buffer.asUint8List(), debugLabel: 'decompressLicenses');
	rawLicenses = await compute<List<int>, String>(utf8.decode, unzippedBytes, debugLabel: 'utf8DecodeLicenses');
	}
	final List<LicenseEntry> licenses = await compute<String, List<LicenseEntry>>(_parseLicenses, rawLicenses, debugLabel: 'parseLicenses');
	licenses.forEach(controller.add);
	await controller.close();
	},
	);
	return controller.stream;
	}

	// This is run in another isolate created by _addLicenses above.
	static List<LicenseEntry> _parseLicenses(String rawLicenses) {
	final String licenseSeparator = '\n${'-' * 80}\n';
	final List<LicenseEntry> result = <LicenseEntry>[];
	final List<String> licenses = rawLicenses.split(licenseSeparator);
	for (final String license in licenses) {
	final int split = license.indexOf('\n\n');
	if (split >= 0) {
	result.add(LicenseEntryWithLineBreaks(
	license.substring(0, split).split('\n'),
	license.substring(split + 2),
	));
	} else {
	result.add(LicenseEntryWithLineBreaks(const <String>[], license));
	}
	}
	return result;
	}

	@override
	void initServiceExtensions() {
	super.initServiceExtensions();

	assert(() {
	registerStringServiceExtension(
	// ext.flutter.evict value=foo.png will cause foo.png to be evicted from
	// the rootBundle cache and cause the entire image cache to be cleared.
	// This is used by hot reload mode to clear out the cache of resources
	// that have changed.
	name: 'evict',
	getter: () async => '',
	setter: (String value) async {
	evict(value);
	},
	);
	return true;
	}());
	}

	/// Called in response to the `ext.flutter.evict` service extension.
	///
	/// This is used by the `flutter` tool during hot reload so that any images
	/// that have changed on disk get cleared from caches.
	@protected
	@mustCallSuper
	void evict(String asset) {
	rootBundle.evict(asset);
	}

	// App life cycle

	/// Initializes the [lifecycleState] with the
	/// [dart:ui.PlatformDispatcher.initialLifecycleState].
	///
	/// Once the [lifecycleState] is populated through any means (including this
	/// method), this method will do nothing. This is because the
	/// [dart:ui.PlatformDispatcher.initialLifecycleState] may already be
	/// stale and it no longer makes sense to use the initial state at dart vm
	/// startup as the current state anymore.
	///
	/// The latest state should be obtained by subscribing to
	/// [WidgetsBindingObserver.didChangeAppLifecycleState].
	@protected
	void readInitialLifecycleStateFromNativeWindow() {
	if (lifecycleState != null) {
	return;
	}
	final AppLifecycleState? state = _parseAppLifecycleMessage(platformDispatcher.initialLifecycleState);
	if (state != null) {
	handleAppLifecycleStateChanged(state);
	}
	}

	Future<String?> _handleLifecycleMessage(String? message) async {
	handleAppLifecycleStateChanged(_parseAppLifecycleMessage(message!)!);
	return null;
	}

	Future<void> _handlePlatformMessage(MethodCall methodCall) async {
	final String method = methodCall.method;
	// There is only one incoming method call currently possible.
	assert(method == 'SystemChrome.systemUIChange');
	final List<dynamic> args = methodCall.arguments as List<dynamic>;
	if (_systemUiChangeCallback != null) {
	await _systemUiChangeCallback!(args[0] as bool);
	}
	}

	static AppLifecycleState? _parseAppLifecycleMessage(String message) {
	switch (message) {
	case 'AppLifecycleState.paused':
	return AppLifecycleState.paused;
	case 'AppLifecycleState.resumed':
	return AppLifecycleState.resumed;
	case 'AppLifecycleState.inactive':
	return AppLifecycleState.inactive;
	case 'AppLifecycleState.detached':
	return AppLifecycleState.detached;
	}
	return null;
	}

	/// The [RestorationManager] synchronizes the restoration data between
	/// engine and framework.
	///
	/// See the docs for [RestorationManager] for a discussion of restoration
	/// state and how it is organized in Flutter.
	///
	/// To use a different [RestorationManager] subclasses can override
	/// [createRestorationManager], which is called to create the instance
	/// returned by this getter.
	RestorationManager get restorationManager => _restorationManager;
	late RestorationManager _restorationManager;

	/// Creates the [RestorationManager] instance available via
	/// [restorationManager].
	///
	/// Can be overridden in subclasses to create a different [RestorationManager].
	@protected
	RestorationManager createRestorationManager() {
	return RestorationManager();
	}

	SystemUiChangeCallback? _systemUiChangeCallback;

	/// Sets the callback for the `SystemChrome.systemUIChange` method call
	/// received on the [SystemChannels.platform] channel.
	///
	/// This is typically not called directly. System UI changes that this method
	/// responds to are associated with [SystemUiMode]s, which are configured
	/// using [SystemChrome]. Use [SystemChrome.setSystemUIChangeCallback] to configure
	/// along with other SystemChrome settings.
	///
	/// See also:
	///
	/// * [SystemChrome.setEnabledSystemUIMode], which specifies the
	/// [SystemUiMode] to have visible when the application is running.
	// ignore: use_setters_to_change_properties, (API predates enforcing the lint)
	void setSystemUiChangeCallback(SystemUiChangeCallback? callback) {
	_systemUiChangeCallback = callback;
	}

	}

	/// Signature for listening to changes in the [SystemUiMode].
	///
	/// Set by [SystemChrome.setSystemUIChangeCallback].
	typedef SystemUiChangeCallback = Future<void> Function(bool systemOverlaysAreVisible);

	/// The default implementation of [BinaryMessenger].
	///
	/// This messenger sends messages from the app-side to the platform-side and
	/// dispatches incoming messages from the platform-side to the appropriate
	/// handler.
	class _DefaultBinaryMessenger extends BinaryMessenger {
	const _DefaultBinaryMessenger._();

	@override
	Future<void> handlePlatformMessage(
	String channel,
	ByteData? message,
	ui.PlatformMessageResponseCallback? callback,
	) async {
	ui.channelBuffers.push(channel, message, (ByteData? data) {
	if (callback != null) {
	callback(data);
	}
	});
	}

	@override
	Future<ByteData?> send(String channel, ByteData? message) {
	final Completer<ByteData?> completer = Completer<ByteData?>();
	// ui.PlatformDispatcher.instance is accessed directly instead of using
	// ServicesBinding.instance.platformDispatcher because this method might be
	// invoked before any binding is initialized. This issue was reported in
	// #27541. It is not ideal to statically access
	// ui.PlatformDispatcher.instance because the PlatformDispatcher may be
	// dependency injected elsewhere with a different instance. However, static
	// access at this location seems to be the least bad option.
	// TODO(ianh): Use ServicesBinding.instance once we have better diagnostics
	// on that getter.
	ui.PlatformDispatcher.instance.sendPlatformMessage(channel, message, (ByteData? reply) {
	try {
	completer.complete(reply);
	} catch (exception, stack) {
	FlutterError.reportError(FlutterErrorDetails(
	exception: exception,
	stack: stack,
	library: 'services library',
	context: ErrorDescription('during a platform message response callback'),
	));
	}
	});
	return completer.future;
	}

	@override
	void setMessageHandler(String channel, MessageHandler? handler) {
	if (handler == null) {
	ui.channelBuffers.clearListener(channel);
	} else {
	ui.channelBuffers.setListener(channel, (ByteData? data, ui.PlatformMessageResponseCallback callback) async {
	ByteData? response;
	try {
	response = await handler(data);
	} catch (exception, stack) {
	FlutterError.reportError(FlutterErrorDetails(
	exception: exception,
	stack: stack,
	library: 'services library',
	context: ErrorDescription('during a platform message callback'),
	));
	} finally {
	callback(response);
	}
	});
	}
	}
	}