packages/flutter/lib/src/widgets/platform_view.dart - mirrors/flutter - Git at Google

 // Copyright 2018 The Chromium 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/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';

 import 'basic.dart';
 import 'debug.dart';
 import 'framework.dart';

 /// Embeds an Android view in the Widget hierarchy.
 ///
 /// Requires Android API level 20 or greater.
 ///
 /// Embedding Android views is an expensive operation and should be avoided when a Flutter
 /// equivalent is possible.
 ///
 /// The embedded Android view is painted just like any other Flutter widget and transformations
 /// apply to it as well.
 ///
 /// {@template flutter.widgets.platformViews.layout}
 /// The widget fills all available space, the parent of this object must provide bounded layout
 /// constraints.
 /// {@endtemplate}
 ///
 /// {@template flutter.widgets.platformViews.gestures}
 /// The widget participates in Flutter's [GestureArena]s, and dispatches touch events to the
 /// platform view iff it won the arena. Specific gestures that should be dispatched to the platform
 /// view can be specified in the `gestureRecognizers` constructor parameter. If
 /// the set of gesture recognizers is empty, a gesture will be dispatched to the platform
 /// view iff it was not claimed by any other gesture recognizer.
 /// {@endtemplate}
 ///
 /// The Android view object is created using a [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html).
 /// Plugins can register platform view factories with [PlatformViewRegistry#registerViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewRegistry.html#registerViewFactory-java.lang.String-io.flutter.plugin.platform.PlatformViewFactory-).
 ///
 /// Registration is typically done in the plugin's registerWith method, e.g:
 ///
 /// ```java
 ///   public static void registerWith(Registrar registrar) {
 ///     registrar.platformViewRegistry().registerViewFactory("webview", WebViewFactory(registrar.messenger()));
 ///   }
 /// ```
 ///
 /// {@template flutter.widgets.platformViews.lifetime}
 /// The platform view's lifetime is the same as the lifetime of the [State] object for this widget.
 /// When the [State] is disposed the platform view (and auxiliary resources) are lazily
 /// released (some resources are immediately released and some by platform garbage collector).
 /// A stateful widget's state is disposed when the widget is removed from the tree or when it is
 /// moved within the tree. If the stateful widget has a key and it's only moved relative to its siblings,
 /// or it has a [GlobalKey] and it's moved within the tree, it will not be disposed.
 /// {@endtemplate}
 class AndroidView extends StatefulWidget {
   /// Creates a widget that embeds an Android view.
   ///
   /// {@template flutter.widgets.platformViews.constructorParams}
   /// The `viewType` and `hitTestBehavior` parameters must not be null.
   /// If `creationParams` is not null then `creationParamsCodec` must not be null.
   /// {@endtemplate}
   const AndroidView({
     Key key,
     @required this.viewType,
     this.onPlatformViewCreated,
     this.hitTestBehavior = PlatformViewHitTestBehavior.opaque,
     this.layoutDirection,
     this.gestureRecognizers,
     this.creationParams,
     this.creationParamsCodec,
   }) : assert(viewType != null),
        assert(hitTestBehavior != null),
        assert(creationParams == null || creationParamsCodec != null),
        super(key: key);

   /// The unique identifier for Android view type to be embedded by this widget.
   ///
   /// A [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html)
   /// for this type must have been registered.
   ///
   /// See also: [AndroidView] for an example of registering a platform view factory.
   final String viewType;

   /// {@template flutter.widgets.platformViews.createdParam}
   /// Callback to invoke after the platform view has been created.
   ///
   /// May be null.
   /// {@endtemplate}
   final PlatformViewCreatedCallback onPlatformViewCreated;

   /// {@template flutter.widgets.platformViews.hittestParam}
   /// How this widget should behave during hit testing.
   ///
   /// This defaults to [PlatformViewHitTestBehavior.opaque].
   /// {@endtemplate}
   final PlatformViewHitTestBehavior hitTestBehavior;

   /// {@template flutter.widgets.platformViews.directionParam}
   /// The text direction to use for the embedded view.
   ///
   /// If this is null, the ambient [Directionality] is used instead.
   /// {@endtemplate}
   final TextDirection layoutDirection;

   /// Which gestures should be forwarded to the Android view.
   ///
   /// {@template flutter.widgets.platformViews.gestureRecognizersDescHead}
   /// The gesture recognizers built by factories in this set participate in the gesture arena for
   /// each pointer that was put down on the widget. If any of these recognizers win the
   /// gesture arena, the entire pointer event sequence starting from the pointer down event
   /// will be dispatched to the platform view.
   ///
   /// When null, an empty set of gesture recognizer factories is used, in which case a pointer event sequence
   /// will only be dispatched to the platform view if no other member of the arena claimed it.
   /// {@endtemplate}
   ///
   /// For example, with the following setup vertical drags will not be dispatched to the Android
   /// view as the vertical drag gesture is claimed by the parent [GestureDetector].
   /// ```dart
   /// GestureDetector(
   ///   onVerticalDragStart: (DragStartDetails d) {},
   ///   child: AndroidView(
   ///     viewType: 'webview',
   ///   ),
   /// )
   /// ```
   /// To get the [AndroidView] to claim the vertical drag gestures we can pass a vertical drag
   /// gesture recognizer factory in [gestureRecognizers] e.g:
   /// ```dart
   /// GestureDetector(
   ///   onVerticalDragStart: (DragStartDetails details) {},
   ///   child: SizedBox(
   ///     width: 200.0,
   ///     height: 100.0,
   ///     child: AndroidView(
   ///       viewType: 'webview',
   ///       gestureRecognizers: <Factory<OneSequenceGestureRecognizer>>[
   ///         new Factory<OneSequenceGestureRecognizer>(
   ///           () => new EagerGestureRecognizer(),
   ///         ),
   ///       ].toSet(),
   ///     ),
   ///   ),
   /// )
   /// ```
   ///
   /// {@template flutter.widgets.platformViews.gestureRecognizersDescFoot}
   /// A platform view can be configured to consume all pointers that were put down in its bounds
   /// by passing a factory for an [EagerGestureRecognizer] in [gestureRecognizers].
   /// [EagerGestureRecognizer] is a special gesture recognizer that immediately claims the gesture
   /// after a pointer down event.
   ///
   /// The `gestureRecognizers` property must not contain more than one factory with the same [Factory.type].
   ///
   /// Changing `gestureRecognizers` results in rejection of any active gesture arenas (if the
   /// platform view is actively participating in an arena).
   /// {@endtemplate}
   // We use OneSequenceGestureRecognizers as they support gesture arena teams.
   // TODO(amirh): get a list of GestureRecognizers here.
   // https://github.com/flutter/flutter/issues/20953
   final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

   /// Passed as the args argument of [PlatformViewFactory#create](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html#create-android.content.Context-int-java.lang.Object-)
   ///
   /// This can be used by plugins to pass constructor parameters to the embedded Android view.
   final dynamic creationParams;

   /// The codec used to encode `creationParams` before sending it to the
   /// platform side. It should match the codec passed to the constructor of [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html#PlatformViewFactory-io.flutter.plugin.common.MessageCodec-).
   ///
   /// This is typically one of: [StandardMessageCodec], [JSONMessageCodec], [StringCodec], or [BinaryCodec].
   ///
   /// This must not be null if [creationParams] is not null.
   final MessageCodec<dynamic> creationParamsCodec;

   @override
   State<AndroidView> createState() => _AndroidViewState();
 }

 // TODO(amirh): describe the embedding mechanism.
 /// Embeds an iOS view in the Widget hierarchy.
 ///
 /// {@macro flutter.rendering.platformView.preview}
 ///
 /// Embedding iOS views is an expensive operation and should be avoided when a Flutter
 /// equivalent is possible.
 ///
 /// {@macro flutter.widgets.platformViews.layout}
 ///
 /// {@macro flutter.widgets.platformViews.gestures}
 ///
 /// {@macro flutter.widgets.platformViews.lifetime}
 ///
 /// Construction of UIViews is done asynchronously, before the UIView is ready this widget paints
 /// nothing while maintaining the same layout constraints.
 class UiKitView extends StatefulWidget {
   /// Creates a widget that embeds an iOS view.
   ///
   /// {@macro flutter.widgets.platformViews.constructorParams}
   UiKitView({ // ignore: prefer_const_constructors_in_immutables
     // TODO(aam): Remove lint ignore above once https://dartbug.com/34297 is fixed
     Key key,
     @required this.viewType,
     this.onPlatformViewCreated,
     this.hitTestBehavior = PlatformViewHitTestBehavior.opaque,
     this.layoutDirection,
     this.creationParams,
     this.creationParamsCodec,
     this.gestureRecognizers,
   }) : assert(viewType != null),
         assert(hitTestBehavior != null),
         assert(creationParams == null || creationParamsCodec != null),
         super(key: key);

   // TODO(amirh): reference the iOS API doc once avaliable.
   /// The unique identifier for iOS view type to be embedded by this widget.
   ///
   /// A PlatformViewFactory for this type must have been registered.
   final String viewType;

   /// {@macro flutter.widgets.platformViews.createdParam}
   final PlatformViewCreatedCallback onPlatformViewCreated;

   /// {@macro flutter.widgets.platformViews.hittestParam}
   final PlatformViewHitTestBehavior hitTestBehavior;

   /// {@macro flutter.widgets.platformViews.directionParam}
   final TextDirection layoutDirection;

   /// Passed as the `arguments` argument of [-\[FlutterPlatformViewFactory createWithFrame:viewIdentifier:arguments:\]](/objcdoc/Protocols/FlutterPlatformViewFactory.html#/c:objc(pl)FlutterPlatformViewFactory(im)createWithFrame:viewIdentifier:arguments:)
   ///
   /// This can be used by plugins to pass constructor parameters to the embedded Android view.
   final dynamic creationParams;

   /// The codec used to encode `creationParams` before sending it to the
   /// platform side. It should match the codec returned by [-\[FlutterPlatformViewFactory createArgsCodec:\]](/objcdoc/Protocols/FlutterPlatformViewFactory.html#/c:objc(pl)FlutterPlatformViewFactory(im)createArgsCodec)
   ///
   /// This is typically one of: [StandardMessageCodec], [JSONMessageCodec], [StringCodec], or [BinaryCodec].
   ///
   /// This must not be null if [creationParams] is not null.
   final MessageCodec<dynamic> creationParamsCodec;

   /// Which gestures should be forwarded to the UIKit view.
   ///
   /// {@macro flutter.widgets.platformViews.gestureRecognizersDescHead}
   ///
   /// For example, with the following setup vertical drags will not be dispatched to the UIKit
   /// view as the vertical drag gesture is claimed by the parent [GestureDetector].
   /// ```dart
   /// GestureDetector(
   ///   onVerticalDragStart: (DragStartDetails details) {},
   ///   child: UiKitView(
   ///     viewType: 'webview',
   ///   ),
   /// )
   /// ```
   /// To get the [UiKitView] to claim the vertical drag gestures we can pass a vertical drag
   /// gesture recognizer factory in [gestureRecognizers] e.g:
   /// ```dart
   /// GestureDetector(
   ///   onVerticalDragStart: (DragStartDetails details) {},
   ///   child: SizedBox(
   ///     width: 200.0,
   ///     height: 100.0,
   ///     child: UiKitView(
   ///       viewType: 'webview',
   ///       gestureRecognizers: <Factory<OneSequenceGestureRecognizer>>[
   ///         new Factory<OneSequenceGestureRecognizer>(
   ///           () => new EagerGestureRecognizer(),
   ///         ),
   ///       ].toSet(),
   ///     ),
   ///   ),
   /// )
   /// ```
   ///
   /// {@macro flutter.widgets.platformViews.gestureRecognizersDescFoot}
   // We use OneSequenceGestureRecognizers as they support gesture arena teams.
   // TODO(amirh): get a list of GestureRecognizers here.
   // https://github.com/flutter/flutter/issues/20953
   final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

   @override
   State<UiKitView> createState() => _UiKitViewState();
 }

 class _AndroidViewState extends State<AndroidView> {
   int _id;
   AndroidViewController _controller;
   TextDirection _layoutDirection;
   bool _initialized = false;

   static final Set<Factory<OneSequenceGestureRecognizer>> _emptyRecognizersSet =
     Set<Factory<OneSequenceGestureRecognizer>>();

   @override
   Widget build(BuildContext context) {
     return _AndroidPlatformView(
         controller: _controller,
         hitTestBehavior: widget.hitTestBehavior,
         gestureRecognizers: widget.gestureRecognizers ?? _emptyRecognizersSet,
     );
   }

   void _initializeOnce() {
     if (_initialized) {
       return;
     }
     _initialized = true;
     _createNewAndroidView();
   }

   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
     final TextDirection newLayoutDirection = _findLayoutDirection();
     final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
     _layoutDirection = newLayoutDirection;

     _initializeOnce();
     if (didChangeLayoutDirection) {
       // The native view will update asynchronously, in the meantime we don't want
       // to block the framework. (so this is intentionally not awaiting).
       _controller.setLayoutDirection(_layoutDirection);
     }
   }

   @override
   void didUpdateWidget(AndroidView oldWidget) {
     super.didUpdateWidget(oldWidget);

     final TextDirection newLayoutDirection = _findLayoutDirection();
     final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
     _layoutDirection = newLayoutDirection;

     if (widget.viewType != oldWidget.viewType) {
       _controller.dispose();
       _createNewAndroidView();
       return;
     }

     if (didChangeLayoutDirection) {
       _controller.setLayoutDirection(_layoutDirection);
     }
   }

   TextDirection _findLayoutDirection() {
     assert(widget.layoutDirection != null || debugCheckHasDirectionality(context));
     return widget.layoutDirection ?? Directionality.of(context);
   }

   @override
   void dispose() {
     _controller.dispose();
     super.dispose();
   }

   void _createNewAndroidView() {
     _id = platformViewsRegistry.getNextPlatformViewId();
     _controller = PlatformViewsService.initAndroidView(
       id: _id,
       viewType: widget.viewType,
       layoutDirection: _layoutDirection,
       onPlatformViewCreated: widget.onPlatformViewCreated,
       creationParams: widget.creationParams,
       creationParamsCodec: widget.creationParamsCodec,
     );
   }
 }

 class _UiKitViewState extends State<UiKitView> {
   UiKitViewController _controller;
   TextDirection _layoutDirection;
   bool _initialized = false;

   static final Set<Factory<OneSequenceGestureRecognizer>> _emptyRecognizersSet =
     Set<Factory<OneSequenceGestureRecognizer>>();

   @override
   Widget build(BuildContext context) {
     if (_controller == null) {
       return const SizedBox.expand();
     }
     return _UiKitPlatformView(
       controller: _controller,
       hitTestBehavior: widget.hitTestBehavior,
       gestureRecognizers: widget.gestureRecognizers ?? _emptyRecognizersSet,
     );
   }

   void _initializeOnce() {
     if (_initialized) {
       return;
     }
     _initialized = true;
     _createNewUiKitView();
   }

   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
     final TextDirection newLayoutDirection = _findLayoutDirection();
     final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
     _layoutDirection = newLayoutDirection;

     _initializeOnce();
     if (didChangeLayoutDirection) {
       // The native view will update asynchronously, in the meantime we don't want
       // to block the framework. (so this is intentionally not awaiting).
       _controller?.setLayoutDirection(_layoutDirection);
     }
   }

   @override
   void didUpdateWidget(UiKitView oldWidget) {
     super.didUpdateWidget(oldWidget);

     final TextDirection newLayoutDirection = _findLayoutDirection();
     final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
     _layoutDirection = newLayoutDirection;

     if (widget.viewType != oldWidget.viewType) {
       _controller?.dispose();
       _createNewUiKitView();
       return;
     }

     if (didChangeLayoutDirection) {
       _controller?.setLayoutDirection(_layoutDirection);
     }
   }

   TextDirection _findLayoutDirection() {
     assert(widget.layoutDirection != null || debugCheckHasDirectionality(context));
     return widget.layoutDirection ?? Directionality.of(context);
   }

   @override
   void dispose() {
     _controller?.dispose();
     super.dispose();
   }

   Future<void> _createNewUiKitView() async {
     final int id = platformViewsRegistry.getNextPlatformViewId();
     final UiKitViewController controller = await PlatformViewsService.initUiKitView(
       id: id,
       viewType: widget.viewType,
       layoutDirection: _layoutDirection,
       creationParams: widget.creationParams,
       creationParamsCodec: widget.creationParamsCodec,
     );
     if (!mounted) {
       controller.dispose();
       return;
     }
     if (widget.onPlatformViewCreated != null) {
       widget.onPlatformViewCreated(id);
     }
     setState(() { _controller = controller; });
   }
 }

 class _AndroidPlatformView extends LeafRenderObjectWidget {
   const _AndroidPlatformView({
     Key key,
     @required this.controller,
     @required this.hitTestBehavior,
     @required this.gestureRecognizers,
   }) : assert(controller != null),
        assert(hitTestBehavior != null),
        assert(gestureRecognizers != null),
        super(key: key);

   final AndroidViewController controller;
   final PlatformViewHitTestBehavior hitTestBehavior;
   final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

   @override
   RenderObject createRenderObject(BuildContext context) =>
       RenderAndroidView(
         viewController: controller,
         hitTestBehavior: hitTestBehavior,
         gestureRecognizers: gestureRecognizers,
       );

   @override
   void updateRenderObject(BuildContext context, RenderAndroidView renderObject) {
     renderObject.viewController = controller;
     renderObject.hitTestBehavior = hitTestBehavior;
     renderObject.updateGestureRecognizers(gestureRecognizers);
   }
 }

 class _UiKitPlatformView extends LeafRenderObjectWidget {
   const _UiKitPlatformView({
     Key key,
     @required this.controller,
     @required this.hitTestBehavior,
     @required this.gestureRecognizers,
   }) : assert(controller != null),
        assert(hitTestBehavior != null),
        assert(gestureRecognizers != null),
        super(key: key);

   final UiKitViewController controller;
   final PlatformViewHitTestBehavior hitTestBehavior;
   final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

   @override
   RenderObject createRenderObject(BuildContext context) {
     return RenderUiKitView(
       viewController: controller,
       hitTestBehavior: hitTestBehavior,
       gestureRecognizers: gestureRecognizers,
     );
   }

   @override
   void updateRenderObject(BuildContext context, RenderUiKitView renderObject) {
     renderObject.viewController = controller;
     renderObject.hitTestBehavior = hitTestBehavior;
     renderObject.updateGestureRecognizers(gestureRecognizers);
   }
 }
	// Copyright 2018 The Chromium 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/foundation.dart';
	import 'package:flutter/gestures.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/services.dart';

	import 'basic.dart';
	import 'debug.dart';
	import 'framework.dart';

	/// Embeds an Android view in the Widget hierarchy.
	///
	/// Requires Android API level 20 or greater.
	///
	/// Embedding Android views is an expensive operation and should be avoided when a Flutter
	/// equivalent is possible.
	///
	/// The embedded Android view is painted just like any other Flutter widget and transformations
	/// apply to it as well.
	///
	/// {@template flutter.widgets.platformViews.layout}
	/// The widget fills all available space, the parent of this object must provide bounded layout
	/// constraints.
	/// {@endtemplate}
	///
	/// {@template flutter.widgets.platformViews.gestures}
	/// The widget participates in Flutter's [GestureArena]s, and dispatches touch events to the
	/// platform view iff it won the arena. Specific gestures that should be dispatched to the platform
	/// view can be specified in the `gestureRecognizers` constructor parameter. If
	/// the set of gesture recognizers is empty, a gesture will be dispatched to the platform
	/// view iff it was not claimed by any other gesture recognizer.
	/// {@endtemplate}
	///
	/// The Android view object is created using a [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html).
	/// Plugins can register platform view factories with [PlatformViewRegistry#registerViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewRegistry.html#registerViewFactory-java.lang.String-io.flutter.plugin.platform.PlatformViewFactory-).
	///
	/// Registration is typically done in the plugin's registerWith method, e.g:
	///
	/// ```java
	/// public static void registerWith(Registrar registrar) {
	/// registrar.platformViewRegistry().registerViewFactory("webview", WebViewFactory(registrar.messenger()));
	/// }
	/// ```
	///
	/// {@template flutter.widgets.platformViews.lifetime}
	/// The platform view's lifetime is the same as the lifetime of the [State] object for this widget.
	/// When the [State] is disposed the platform view (and auxiliary resources) are lazily
	/// released (some resources are immediately released and some by platform garbage collector).
	/// A stateful widget's state is disposed when the widget is removed from the tree or when it is
	/// moved within the tree. If the stateful widget has a key and it's only moved relative to its siblings,
	/// or it has a [GlobalKey] and it's moved within the tree, it will not be disposed.
	/// {@endtemplate}
	class AndroidView extends StatefulWidget {
	/// Creates a widget that embeds an Android view.
	///
	/// {@template flutter.widgets.platformViews.constructorParams}
	/// The `viewType` and `hitTestBehavior` parameters must not be null.
	/// If `creationParams` is not null then `creationParamsCodec` must not be null.
	/// {@endtemplate}
	const AndroidView({
	Key key,
	@required this.viewType,
	this.onPlatformViewCreated,
	this.hitTestBehavior = PlatformViewHitTestBehavior.opaque,
	this.layoutDirection,
	this.gestureRecognizers,
	this.creationParams,
	this.creationParamsCodec,
	}) : assert(viewType != null),
	assert(hitTestBehavior != null),
	assert(creationParams == null \|\| creationParamsCodec != null),
	super(key: key);

	/// The unique identifier for Android view type to be embedded by this widget.
	///
	/// A [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html)
	/// for this type must have been registered.
	///
	/// See also: [AndroidView] for an example of registering a platform view factory.
	final String viewType;

	/// {@template flutter.widgets.platformViews.createdParam}
	/// Callback to invoke after the platform view has been created.
	///
	/// May be null.
	/// {@endtemplate}
	final PlatformViewCreatedCallback onPlatformViewCreated;

	/// {@template flutter.widgets.platformViews.hittestParam}
	/// How this widget should behave during hit testing.
	///
	/// This defaults to [PlatformViewHitTestBehavior.opaque].
	/// {@endtemplate}
	final PlatformViewHitTestBehavior hitTestBehavior;

	/// {@template flutter.widgets.platformViews.directionParam}
	/// The text direction to use for the embedded view.
	///
	/// If this is null, the ambient [Directionality] is used instead.
	/// {@endtemplate}
	final TextDirection layoutDirection;

	/// Which gestures should be forwarded to the Android view.
	///
	/// {@template flutter.widgets.platformViews.gestureRecognizersDescHead}
	/// The gesture recognizers built by factories in this set participate in the gesture arena for
	/// each pointer that was put down on the widget. If any of these recognizers win the
	/// gesture arena, the entire pointer event sequence starting from the pointer down event
	/// will be dispatched to the platform view.
	///
	/// When null, an empty set of gesture recognizer factories is used, in which case a pointer event sequence
	/// will only be dispatched to the platform view if no other member of the arena claimed it.
	/// {@endtemplate}
	///
	/// For example, with the following setup vertical drags will not be dispatched to the Android
	/// view as the vertical drag gesture is claimed by the parent [GestureDetector].
	/// ```dart
	/// GestureDetector(
	/// onVerticalDragStart: (DragStartDetails d) {},
	/// child: AndroidView(
	/// viewType: 'webview',
	/// ),
	/// )
	/// ```
	/// To get the [AndroidView] to claim the vertical drag gestures we can pass a vertical drag
	/// gesture recognizer factory in [gestureRecognizers] e.g:
	/// ```dart
	/// GestureDetector(
	/// onVerticalDragStart: (DragStartDetails details) {},
	/// child: SizedBox(
	/// width: 200.0,
	/// height: 100.0,
	/// child: AndroidView(
	/// viewType: 'webview',
	/// gestureRecognizers: <Factory<OneSequenceGestureRecognizer>>[
	/// new Factory<OneSequenceGestureRecognizer>(
	/// () => new EagerGestureRecognizer(),
	/// ),
	/// ].toSet(),
	/// ),
	/// ),
	/// )
	/// ```
	///
	/// {@template flutter.widgets.platformViews.gestureRecognizersDescFoot}
	/// A platform view can be configured to consume all pointers that were put down in its bounds
	/// by passing a factory for an [EagerGestureRecognizer] in [gestureRecognizers].
	/// [EagerGestureRecognizer] is a special gesture recognizer that immediately claims the gesture
	/// after a pointer down event.
	///
	/// The `gestureRecognizers` property must not contain more than one factory with the same [Factory.type].
	///
	/// Changing `gestureRecognizers` results in rejection of any active gesture arenas (if the
	/// platform view is actively participating in an arena).
	/// {@endtemplate}
	// We use OneSequenceGestureRecognizers as they support gesture arena teams.
	// TODO(amirh): get a list of GestureRecognizers here.
	// https://github.com/flutter/flutter/issues/20953
	final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

	/// Passed as the args argument of [PlatformViewFactory#create](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html#create-android.content.Context-int-java.lang.Object-)
	///
	/// This can be used by plugins to pass constructor parameters to the embedded Android view.
	final dynamic creationParams;

	/// The codec used to encode `creationParams` before sending it to the
	/// platform side. It should match the codec passed to the constructor of [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html#PlatformViewFactory-io.flutter.plugin.common.MessageCodec-).
	///
	/// This is typically one of: [StandardMessageCodec], [JSONMessageCodec], [StringCodec], or [BinaryCodec].
	///
	/// This must not be null if [creationParams] is not null.
	final MessageCodec<dynamic> creationParamsCodec;

	@override
	State<AndroidView> createState() => _AndroidViewState();
	}

	// TODO(amirh): describe the embedding mechanism.
	/// Embeds an iOS view in the Widget hierarchy.
	///
	/// {@macro flutter.rendering.platformView.preview}
	///
	/// Embedding iOS views is an expensive operation and should be avoided when a Flutter
	/// equivalent is possible.
	///
	/// {@macro flutter.widgets.platformViews.layout}
	///
	/// {@macro flutter.widgets.platformViews.gestures}
	///
	/// {@macro flutter.widgets.platformViews.lifetime}
	///
	/// Construction of UIViews is done asynchronously, before the UIView is ready this widget paints
	/// nothing while maintaining the same layout constraints.
	class UiKitView extends StatefulWidget {
	/// Creates a widget that embeds an iOS view.
	///
	/// {@macro flutter.widgets.platformViews.constructorParams}
	UiKitView({ // ignore: prefer_const_constructors_in_immutables
	// TODO(aam): Remove lint ignore above once https://dartbug.com/34297 is fixed
	Key key,
	@required this.viewType,
	this.onPlatformViewCreated,
	this.hitTestBehavior = PlatformViewHitTestBehavior.opaque,
	this.layoutDirection,
	this.creationParams,
	this.creationParamsCodec,
	this.gestureRecognizers,
	}) : assert(viewType != null),
	assert(hitTestBehavior != null),
	assert(creationParams == null \|\| creationParamsCodec != null),
	super(key: key);

	// TODO(amirh): reference the iOS API doc once avaliable.
	/// The unique identifier for iOS view type to be embedded by this widget.
	///
	/// A PlatformViewFactory for this type must have been registered.
	final String viewType;

	/// {@macro flutter.widgets.platformViews.createdParam}
	final PlatformViewCreatedCallback onPlatformViewCreated;

	/// {@macro flutter.widgets.platformViews.hittestParam}
	final PlatformViewHitTestBehavior hitTestBehavior;

	/// {@macro flutter.widgets.platformViews.directionParam}
	final TextDirection layoutDirection;

	/// Passed as the `arguments` argument of [-\[FlutterPlatformViewFactory createWithFrame:viewIdentifier:arguments:\]](/objcdoc/Protocols/FlutterPlatformViewFactory.html#/c:objc(pl)FlutterPlatformViewFactory(im)createWithFrame:viewIdentifier:arguments:)
	///
	/// This can be used by plugins to pass constructor parameters to the embedded Android view.
	final dynamic creationParams;

	/// The codec used to encode `creationParams` before sending it to the
	/// platform side. It should match the codec returned by [-\[FlutterPlatformViewFactory createArgsCodec:\]](/objcdoc/Protocols/FlutterPlatformViewFactory.html#/c:objc(pl)FlutterPlatformViewFactory(im)createArgsCodec)
	///
	/// This is typically one of: [StandardMessageCodec], [JSONMessageCodec], [StringCodec], or [BinaryCodec].
	///
	/// This must not be null if [creationParams] is not null.
	final MessageCodec<dynamic> creationParamsCodec;

	/// Which gestures should be forwarded to the UIKit view.
	///
	/// {@macro flutter.widgets.platformViews.gestureRecognizersDescHead}
	///
	/// For example, with the following setup vertical drags will not be dispatched to the UIKit
	/// view as the vertical drag gesture is claimed by the parent [GestureDetector].
	/// ```dart
	/// GestureDetector(
	/// onVerticalDragStart: (DragStartDetails details) {},
	/// child: UiKitView(
	/// viewType: 'webview',
	/// ),
	/// )
	/// ```
	/// To get the [UiKitView] to claim the vertical drag gestures we can pass a vertical drag
	/// gesture recognizer factory in [gestureRecognizers] e.g:
	/// ```dart
	/// GestureDetector(
	/// onVerticalDragStart: (DragStartDetails details) {},
	/// child: SizedBox(
	/// width: 200.0,
	/// height: 100.0,
	/// child: UiKitView(
	/// viewType: 'webview',
	/// gestureRecognizers: <Factory<OneSequenceGestureRecognizer>>[
	/// new Factory<OneSequenceGestureRecognizer>(
	/// () => new EagerGestureRecognizer(),
	/// ),
	/// ].toSet(),
	/// ),
	/// ),
	/// )
	/// ```
	///
	/// {@macro flutter.widgets.platformViews.gestureRecognizersDescFoot}
	// We use OneSequenceGestureRecognizers as they support gesture arena teams.
	// TODO(amirh): get a list of GestureRecognizers here.
	// https://github.com/flutter/flutter/issues/20953
	final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

	@override
	State<UiKitView> createState() => _UiKitViewState();
	}

	class _AndroidViewState extends State<AndroidView> {
	int _id;
	AndroidViewController _controller;
	TextDirection _layoutDirection;
	bool _initialized = false;

	static final Set<Factory<OneSequenceGestureRecognizer>> _emptyRecognizersSet =
	Set<Factory<OneSequenceGestureRecognizer>>();

	@override
	Widget build(BuildContext context) {
	return _AndroidPlatformView(
	controller: _controller,
	hitTestBehavior: widget.hitTestBehavior,
	gestureRecognizers: widget.gestureRecognizers ?? _emptyRecognizersSet,
	);
	}

	void _initializeOnce() {
	if (_initialized) {
	return;
	}
	_initialized = true;
	_createNewAndroidView();
	}

	@override
	void didChangeDependencies() {
	super.didChangeDependencies();
	final TextDirection newLayoutDirection = _findLayoutDirection();
	final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
	_layoutDirection = newLayoutDirection;

	_initializeOnce();
	if (didChangeLayoutDirection) {
	// The native view will update asynchronously, in the meantime we don't want
	// to block the framework. (so this is intentionally not awaiting).
	_controller.setLayoutDirection(_layoutDirection);
	}
	}

	@override
	void didUpdateWidget(AndroidView oldWidget) {
	super.didUpdateWidget(oldWidget);

	final TextDirection newLayoutDirection = _findLayoutDirection();
	final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
	_layoutDirection = newLayoutDirection;

	if (widget.viewType != oldWidget.viewType) {
	_controller.dispose();
	_createNewAndroidView();
	return;
	}

	if (didChangeLayoutDirection) {
	_controller.setLayoutDirection(_layoutDirection);
	}
	}

	TextDirection _findLayoutDirection() {
	assert(widget.layoutDirection != null \|\| debugCheckHasDirectionality(context));
	return widget.layoutDirection ?? Directionality.of(context);
	}

	@override
	void dispose() {
	_controller.dispose();
	super.dispose();
	}

	void _createNewAndroidView() {
	_id = platformViewsRegistry.getNextPlatformViewId();
	_controller = PlatformViewsService.initAndroidView(
	id: _id,
	viewType: widget.viewType,
	layoutDirection: _layoutDirection,
	onPlatformViewCreated: widget.onPlatformViewCreated,
	creationParams: widget.creationParams,
	creationParamsCodec: widget.creationParamsCodec,
	);
	}
	}

	class _UiKitViewState extends State<UiKitView> {
	UiKitViewController _controller;
	TextDirection _layoutDirection;
	bool _initialized = false;

	static final Set<Factory<OneSequenceGestureRecognizer>> _emptyRecognizersSet =
	Set<Factory<OneSequenceGestureRecognizer>>();

	@override
	Widget build(BuildContext context) {
	if (_controller == null) {
	return const SizedBox.expand();
	}
	return _UiKitPlatformView(
	controller: _controller,
	hitTestBehavior: widget.hitTestBehavior,
	gestureRecognizers: widget.gestureRecognizers ?? _emptyRecognizersSet,
	);
	}

	void _initializeOnce() {
	if (_initialized) {
	return;
	}
	_initialized = true;
	_createNewUiKitView();
	}

	@override
	void didChangeDependencies() {
	super.didChangeDependencies();
	final TextDirection newLayoutDirection = _findLayoutDirection();
	final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
	_layoutDirection = newLayoutDirection;

	_initializeOnce();
	if (didChangeLayoutDirection) {
	// The native view will update asynchronously, in the meantime we don't want
	// to block the framework. (so this is intentionally not awaiting).
	_controller?.setLayoutDirection(_layoutDirection);
	}
	}

	@override
	void didUpdateWidget(UiKitView oldWidget) {
	super.didUpdateWidget(oldWidget);

	final TextDirection newLayoutDirection = _findLayoutDirection();
	final bool didChangeLayoutDirection = _layoutDirection != newLayoutDirection;
	_layoutDirection = newLayoutDirection;

	if (widget.viewType != oldWidget.viewType) {
	_controller?.dispose();
	_createNewUiKitView();
	return;
	}

	if (didChangeLayoutDirection) {
	_controller?.setLayoutDirection(_layoutDirection);
	}
	}

	TextDirection _findLayoutDirection() {
	assert(widget.layoutDirection != null \|\| debugCheckHasDirectionality(context));
	return widget.layoutDirection ?? Directionality.of(context);
	}

	@override
	void dispose() {
	_controller?.dispose();
	super.dispose();
	}

	Future<void> _createNewUiKitView() async {
	final int id = platformViewsRegistry.getNextPlatformViewId();
	final UiKitViewController controller = await PlatformViewsService.initUiKitView(
	id: id,
	viewType: widget.viewType,
	layoutDirection: _layoutDirection,
	creationParams: widget.creationParams,
	creationParamsCodec: widget.creationParamsCodec,
	);
	if (!mounted) {
	controller.dispose();
	return;
	}
	if (widget.onPlatformViewCreated != null) {
	widget.onPlatformViewCreated(id);
	}
	setState(() { _controller = controller; });
	}
	}

	class _AndroidPlatformView extends LeafRenderObjectWidget {
	const _AndroidPlatformView({
	Key key,
	@required this.controller,
	@required this.hitTestBehavior,
	@required this.gestureRecognizers,
	}) : assert(controller != null),
	assert(hitTestBehavior != null),
	assert(gestureRecognizers != null),
	super(key: key);

	final AndroidViewController controller;
	final PlatformViewHitTestBehavior hitTestBehavior;
	final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

	@override
	RenderObject createRenderObject(BuildContext context) =>
	RenderAndroidView(
	viewController: controller,
	hitTestBehavior: hitTestBehavior,
	gestureRecognizers: gestureRecognizers,
	);

	@override
	void updateRenderObject(BuildContext context, RenderAndroidView renderObject) {
	renderObject.viewController = controller;
	renderObject.hitTestBehavior = hitTestBehavior;
	renderObject.updateGestureRecognizers(gestureRecognizers);
	}
	}

	class _UiKitPlatformView extends LeafRenderObjectWidget {
	const _UiKitPlatformView({
	Key key,
	@required this.controller,
	@required this.hitTestBehavior,
	@required this.gestureRecognizers,
	}) : assert(controller != null),
	assert(hitTestBehavior != null),
	assert(gestureRecognizers != null),
	super(key: key);

	final UiKitViewController controller;
	final PlatformViewHitTestBehavior hitTestBehavior;
	final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

	@override
	RenderObject createRenderObject(BuildContext context) {
	return RenderUiKitView(
	viewController: controller,
	hitTestBehavior: hitTestBehavior,
	gestureRecognizers: gestureRecognizers,
	);
	}

	@override
	void updateRenderObject(BuildContext context, RenderUiKitView renderObject) {
	renderObject.viewController = controller;
	renderObject.hitTestBehavior = hitTestBehavior;
	renderObject.updateGestureRecognizers(gestureRecognizers);
	}
	}