packages/webview_flutter/lib/webview_flutter.dart - mirrors/plugins - 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 'dart:async';

 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';

 typedef void WebViewCreatedCallback(WebViewController controller);

 enum JavascriptMode {
   /// JavaScript execution is disabled.
   disabled,

   /// JavaScript execution is not restricted.
   unrestricted,
 }

 /// A message that was sent by JavaScript code running in a [WebView].
 class JavascriptMessage {
   /// Constructs a JavaScript message object.
   ///
   /// The `message` parameter must not be null.
   const JavascriptMessage(this.message) : assert(message != null);

   /// The contents of the message that was sent by the JavaScript code.
   final String message;
 }

 /// Callback type for handling messages sent from Javascript running in a web view.
 typedef void JavascriptMessageHandler(JavascriptMessage message);

 final RegExp _validChannelNames = RegExp('^[a-zA-Z_][a-zA-Z0-9]*\$');

 /// A named channel for receiving messaged from JavaScript code running inside a web view.
 class JavascriptChannel {
   /// Constructs a Javascript channel.
   ///
   /// The parameters `name` and `onMessageReceived` must not be null.
   JavascriptChannel({
     @required this.name,
     @required this.onMessageReceived,
   })  : assert(name != null),
         assert(onMessageReceived != null),
         assert(_validChannelNames.hasMatch(name));

   /// The channel's name.
   ///
   /// Passing this channel object as part of a [WebView.javascriptChannels] adds a channel object to
   /// the Javascript window object's property named `name`.
   ///
   /// The name must start with a letter or underscore(_), followed by any combination of those
   /// characters plus digits.
   ///
   /// Note that any JavaScript existing `window` property with this name will be overriden.
   ///
   /// See also [WebView.javascriptChannels] for more details on the channel registration mechanism.
   final String name;

   /// A callback that's invoked when a message is received through the channel.
   final JavascriptMessageHandler onMessageReceived;
 }

 /// A web view widget for showing html content.
 class WebView extends StatefulWidget {
   /// Creates a new web view.
   ///
   /// The web view can be controlled using a `WebViewController` that is passed to the
   /// `onWebViewCreated` callback once the web view is created.
   ///
   /// The `javascriptMode` parameter must not be null.
   const WebView({
     Key key,
     this.onWebViewCreated,
     this.initialUrl,
     this.javascriptMode = JavascriptMode.disabled,
     this.javascriptChannels,
     this.gestureRecognizers,
   })  : assert(javascriptMode != null),
         super(key: key);

   /// If not null invoked once the web view is created.
   final WebViewCreatedCallback onWebViewCreated;

   /// Which gestures should be consumed by the web view.
   ///
   /// It is possible for other gesture recognizers to be competing with the web view on pointer
   /// events, e.g if the web view is inside a [ListView] the [ListView] will want to handle
   /// vertical drags. The web view will claim gestures that are recognized by any of the
   /// recognizers on this list.
   ///
   /// When this set is empty or null, the web view will only handle pointer events for gestures that
   /// were not claimed by any other gesture recognizer.
   final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

   /// The initial URL to load.
   final String initialUrl;

   /// Whether Javascript execution is enabled.
   final JavascriptMode javascriptMode;

   /// The set of [JavascriptChannel]s available to JavaScript code running in the web view.
   ///
   /// For each [JavascriptChannel] in the set, a channel object is made available for the
   /// JavaScript code in a window property named [JavascriptChannel.name].
   /// The JavaScript code can then call `postMessage` on that object to send a message that will be
   /// passed to [JavascriptChannel.onMessageReceived].
   ///
   /// For example for the following JavascriptChannel:
   ///
   /// ```dart
   /// JavascriptChannel(name: 'Print', onMessageReceived: (String message) { print(message); });
   /// ```
   ///
   /// JavaScript code can call:
   ///
   /// ```javascript
   /// Print.postMessage('Hello');
   /// ```
   ///
   /// To asynchronously invoke the message handler which will print the message to standard output.
   ///
   /// Adding a new JavaScript channel only takes affect after the next page is loaded.
   ///
   /// Set values must not be null. A [JavascriptChannel.name] cannot be the same for multiple
   /// channels in the list.
   ///
   /// A null value is equivalent to an empty set.
   final Set<JavascriptChannel> javascriptChannels;

   @override
   State<StatefulWidget> createState() => _WebViewState();
 }

 class _WebViewState extends State<WebView> {
   final Completer<WebViewController> _controller =
       Completer<WebViewController>();

   _WebSettings _settings;

   @override
   Widget build(BuildContext context) {
     if (defaultTargetPlatform == TargetPlatform.android) {
       return GestureDetector(
         // We prevent text selection by intercepting the long press event.
         // This is a temporary stop gap due to issues with text selection on Android:
         // https://github.com/flutter/flutter/issues/24585 - the text selection
         // dialog is not responding to touch events.
         // https://github.com/flutter/flutter/issues/24584 - the text selection
         // handles are not showing.
         // TODO(amirh): remove this when the issues above are fixed.
         onLongPress: () {},
         child: AndroidView(
           viewType: 'plugins.flutter.io/webview',
           onPlatformViewCreated: _onPlatformViewCreated,
           gestureRecognizers: widget.gestureRecognizers,
           // WebView content is not affected by the Android view's layout direction,
           // we explicitly set it here so that the widget doesn't require an ambient
           // directionality.
           layoutDirection: TextDirection.rtl,
           creationParams: _CreationParams.fromWidget(widget).toMap(),
           creationParamsCodec: const StandardMessageCodec(),
         ),
       );
     } else if (defaultTargetPlatform == TargetPlatform.iOS) {
       return UiKitView(
         viewType: 'plugins.flutter.io/webview',
         onPlatformViewCreated: _onPlatformViewCreated,
         gestureRecognizers: widget.gestureRecognizers,
         creationParams: _CreationParams.fromWidget(widget).toMap(),
         creationParamsCodec: const StandardMessageCodec(),
       );
     }
     return Text(
         '$defaultTargetPlatform is not yet supported by the webview_flutter plugin');
   }

   @override
   void initState() {
     super.initState();
     _assertJavascriptChannelNamesAreUnique();
   }

   @override
   void didUpdateWidget(WebView oldWidget) {
     super.didUpdateWidget(oldWidget);
     _assertJavascriptChannelNamesAreUnique();
     _updateConfiguration(_WebSettings.fromWidget(widget));
   }

   Future<void> _updateConfiguration(_WebSettings settings) async {
     _settings = settings;
     final WebViewController controller = await _controller.future;
     controller._updateSettings(settings);
     controller._updateJavascriptChannels(widget.javascriptChannels);
   }

   void _onPlatformViewCreated(int id) {
     final WebViewController controller = WebViewController._(
       id,
       _WebSettings.fromWidget(widget),
       widget.javascriptChannels,
     );
     _controller.complete(controller);
     if (widget.onWebViewCreated != null) {
       widget.onWebViewCreated(controller);
     }
   }

   void _assertJavascriptChannelNamesAreUnique() {
     if (widget.javascriptChannels == null ||
         widget.javascriptChannels.isEmpty) {
       return;
     }
     assert(_extractChannelNames(widget.javascriptChannels).length ==
         widget.javascriptChannels.length);
   }
 }

 Set<String> _extractChannelNames(Set<JavascriptChannel> channels) {
   final Set<String> channelNames = channels == null
       ? Set<String>()
       : channels.map((JavascriptChannel channel) => channel.name).toSet();
   return channelNames;
 }

 class _CreationParams {
   _CreationParams(
       {this.initialUrl, this.settings, this.javascriptChannelNames});

   static _CreationParams fromWidget(WebView widget) {
     return _CreationParams(
       initialUrl: widget.initialUrl,
       settings: _WebSettings.fromWidget(widget),
       javascriptChannelNames:
           _extractChannelNames(widget.javascriptChannels).toList(),
     );
   }

   final String initialUrl;

   final _WebSettings settings;

   final List<String> javascriptChannelNames;

   Map<String, dynamic> toMap() {
     return <String, dynamic>{
       'initialUrl': initialUrl,
       'settings': settings.toMap(),
       'javascriptChannelNames': javascriptChannelNames,
     };
   }
 }

 class _WebSettings {
   _WebSettings({
     this.javascriptMode,
   });

   static _WebSettings fromWidget(WebView widget) {
     return _WebSettings(javascriptMode: widget.javascriptMode);
   }

   final JavascriptMode javascriptMode;

   Map<String, dynamic> toMap() {
     return <String, dynamic>{
       'jsMode': javascriptMode.index,
     };
   }

   Map<String, dynamic> updatesMap(_WebSettings newSettings) {
     if (javascriptMode == newSettings.javascriptMode) {
       return null;
     }
     return <String, dynamic>{
       'jsMode': newSettings.javascriptMode.index,
     };
   }
 }

 /// Controls a [WebView].
 ///
 /// A [WebViewController] instance can be obtained by setting the [WebView.onWebViewCreated]
 /// callback for a [WebView] widget.
 class WebViewController {
   WebViewController._(
       int id, this._settings, Set<JavascriptChannel> javascriptChannels)
       : _channel = MethodChannel('plugins.flutter.io/webview_$id') {
     _updateJavascriptChannelsFromSet(javascriptChannels);
     _channel.setMethodCallHandler(_onMethodCall);
   }

   final MethodChannel _channel;

   _WebSettings _settings;

   // Maps a channel name to a channel.
   Map<String, JavascriptChannel> _javascriptChannels =
       <String, JavascriptChannel>{};

   Future<void> _onMethodCall(MethodCall call) async {
     switch (call.method) {
       case 'javascriptChannelMessage':
         final String channel = call.arguments['channel'];
         final String message = call.arguments['message'];
         _javascriptChannels[channel]
             .onMessageReceived(JavascriptMessage(message));
         break;
     }
   }

   /// Loads the specified URL.
   ///
   /// `url` must not be null.
   ///
   /// Throws an ArgumentError if `url` is not a valid URL string.
   Future<void> loadUrl(String url) async {
     assert(url != null);
     _validateUrlString(url);
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     return _channel.invokeMethod('loadUrl', url);
   }

   /// Accessor to the current URL that the WebView is displaying.
   ///
   /// If [WebView.initialUrl] was never specified, returns `null`.
   /// Note that this operation is asynchronous, and it is possible that the
   /// current URL changes again by the time this function returns (in other
   /// words, by the time this future completes, the WebView may be displaying a
   /// different URL).
   Future<String> currentUrl() async {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     final String url = await _channel.invokeMethod('currentUrl');
     return url;
   }

   /// Checks whether there's a back history item.
   ///
   /// Note that this operation is asynchronous, and it is possible that the "canGoBack" state has
   /// changed by the time the future completed.
   Future<bool> canGoBack() async {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     final bool canGoBack = await _channel.invokeMethod("canGoBack");
     return canGoBack;
   }

   /// Checks whether there's a forward history item.
   ///
   /// Note that this operation is asynchronous, and it is possible that the "canGoForward" state has
   /// changed by the time the future completed.
   Future<bool> canGoForward() async {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     final bool canGoForward = await _channel.invokeMethod("canGoForward");
     return canGoForward;
   }

   /// Goes back in the history of this WebView.
   ///
   /// If there is no back history item this is a no-op.
   Future<void> goBack() async {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     return _channel.invokeMethod("goBack");
   }

   /// Goes forward in the history of this WebView.
   ///
   /// If there is no forward history item this is a no-op.
   Future<void> goForward() async {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     return _channel.invokeMethod("goForward");
   }

   /// Reloads the current URL.
   Future<void> reload() async {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     return _channel.invokeMethod("reload");
   }

   Future<void> _updateSettings(_WebSettings setting) async {
     final Map<String, dynamic> updateMap = _settings.updatesMap(setting);
     if (updateMap == null) {
       return null;
     }
     _settings = setting;
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     return _channel.invokeMethod('updateSettings', updateMap);
   }

   Future<void> _updateJavascriptChannels(
       Set<JavascriptChannel> newChannels) async {
     final Set<String> currentChannels = _javascriptChannels.keys.toSet();
     final Set<String> newChannelNames = _extractChannelNames(newChannels);
     final Set<String> channelsToAdd =
         newChannelNames.difference(currentChannels);
     final Set<String> channelsToRemove =
         currentChannels.difference(newChannelNames);
     if (channelsToRemove.isNotEmpty) {
       // TODO(amirh): remove this when the invokeMethod update makes it to stable Flutter.
       // https://github.com/flutter/flutter/issues/26431
       // ignore: strong_mode_implicit_dynamic_method
       _channel.invokeMethod(
           'removeJavascriptChannels', channelsToRemove.toList());
     }
     if (channelsToAdd.isNotEmpty) {
       // TODO(amirh): remove this when the invokeMethod update makes it to stable Flutter.
       // https://github.com/flutter/flutter/issues/26431
       // ignore: strong_mode_implicit_dynamic_method
       _channel.invokeMethod('addJavascriptChannels', channelsToAdd.toList());
     }
     _updateJavascriptChannelsFromSet(newChannels);
   }

   void _updateJavascriptChannelsFromSet(Set<JavascriptChannel> channels) {
     _javascriptChannels.clear();
     if (channels == null) {
       return;
     }
     for (JavascriptChannel channel in channels) {
       _javascriptChannels[channel.name] = channel;
     }
   }

   /// Evaluates a JavaScript expression in the context of the current page.
   ///
   /// On Android returns the evaluation result as a JSON formatted string.
   ///
   /// On iOS depending on the value type the return value would be one of:
   ///
   ///  - For primitive JavaScript types: the value string formatted (e.g JavaScript 100 returns '100').
   ///  - For JavaScript arrays of supported types: a string formatted NSArray(e.g '(1,2,3), note that the string for NSArray is formatted and might contain newlines and extra spaces.').
   ///  - Other non-primitive types are not supported on iOS and will complete the Future with an error.
   ///
   /// The Future completes with an error if a JavaScript error occurred, or on iOS, if the type of the
   /// evaluated expression is not supported as described above.
   Future<String> evaluateJavascript(String javascriptString) async {
     if (_settings.javascriptMode == JavascriptMode.disabled) {
       throw FlutterError(
           'JavaScript mode must be enabled/unrestricted when calling evaluateJavascript.');
     }
     if (javascriptString == null) {
       throw ArgumentError('The argument javascriptString must not be null. ');
     }
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
     final String result =
         await _channel.invokeMethod('evaluateJavascript', javascriptString);
     return result;
   }
 }

 // Throws an ArgumentError if `url` is not a valid URL string.
 void _validateUrlString(String url) {
   try {
     final Uri uri = Uri.parse(url);
     if (uri.scheme.isEmpty) {
       throw ArgumentError('Missing scheme in URL string: "$url"');
     }
   } on FormatException catch (e) {
     throw ArgumentError(e);
   }
 }
	// 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 'dart:async';

	import 'package:flutter/foundation.dart';
	import 'package:flutter/gestures.dart';
	import 'package:flutter/services.dart';
	import 'package:flutter/widgets.dart';

	typedef void WebViewCreatedCallback(WebViewController controller);

	enum JavascriptMode {
	/// JavaScript execution is disabled.
	disabled,

	/// JavaScript execution is not restricted.
	unrestricted,
	}

	/// A message that was sent by JavaScript code running in a [WebView].
	class JavascriptMessage {
	/// Constructs a JavaScript message object.
	///
	/// The `message` parameter must not be null.
	const JavascriptMessage(this.message) : assert(message != null);

	/// The contents of the message that was sent by the JavaScript code.
	final String message;
	}

	/// Callback type for handling messages sent from Javascript running in a web view.
	typedef void JavascriptMessageHandler(JavascriptMessage message);

	final RegExp _validChannelNames = RegExp('^[a-zA-Z_][a-zA-Z0-9]*\$');

	/// A named channel for receiving messaged from JavaScript code running inside a web view.
	class JavascriptChannel {
	/// Constructs a Javascript channel.
	///
	/// The parameters `name` and `onMessageReceived` must not be null.
	JavascriptChannel({
	@required this.name,
	@required this.onMessageReceived,
	}) : assert(name != null),
	assert(onMessageReceived != null),
	assert(_validChannelNames.hasMatch(name));

	/// The channel's name.
	///
	/// Passing this channel object as part of a [WebView.javascriptChannels] adds a channel object to
	/// the Javascript window object's property named `name`.
	///
	/// The name must start with a letter or underscore(_), followed by any combination of those
	/// characters plus digits.
	///
	/// Note that any JavaScript existing `window` property with this name will be overriden.
	///
	/// See also [WebView.javascriptChannels] for more details on the channel registration mechanism.
	final String name;

	/// A callback that's invoked when a message is received through the channel.
	final JavascriptMessageHandler onMessageReceived;
	}

	/// A web view widget for showing html content.
	class WebView extends StatefulWidget {
	/// Creates a new web view.
	///
	/// The web view can be controlled using a `WebViewController` that is passed to the
	/// `onWebViewCreated` callback once the web view is created.
	///
	/// The `javascriptMode` parameter must not be null.
	const WebView({
	Key key,
	this.onWebViewCreated,
	this.initialUrl,
	this.javascriptMode = JavascriptMode.disabled,
	this.javascriptChannels,
	this.gestureRecognizers,
	}) : assert(javascriptMode != null),
	super(key: key);

	/// If not null invoked once the web view is created.
	final WebViewCreatedCallback onWebViewCreated;

	/// Which gestures should be consumed by the web view.
	///
	/// It is possible for other gesture recognizers to be competing with the web view on pointer
	/// events, e.g if the web view is inside a [ListView] the [ListView] will want to handle
	/// vertical drags. The web view will claim gestures that are recognized by any of the
	/// recognizers on this list.
	///
	/// When this set is empty or null, the web view will only handle pointer events for gestures that
	/// were not claimed by any other gesture recognizer.
	final Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;

	/// The initial URL to load.
	final String initialUrl;

	/// Whether Javascript execution is enabled.
	final JavascriptMode javascriptMode;

	/// The set of [JavascriptChannel]s available to JavaScript code running in the web view.
	///
	/// For each [JavascriptChannel] in the set, a channel object is made available for the
	/// JavaScript code in a window property named [JavascriptChannel.name].
	/// The JavaScript code can then call `postMessage` on that object to send a message that will be
	/// passed to [JavascriptChannel.onMessageReceived].
	///
	/// For example for the following JavascriptChannel:
	///
	/// ```dart
	/// JavascriptChannel(name: 'Print', onMessageReceived: (String message) { print(message); });
	/// ```
	///
	/// JavaScript code can call:
	///
	/// ```javascript
	/// Print.postMessage('Hello');
	/// ```
	///
	/// To asynchronously invoke the message handler which will print the message to standard output.
	///
	/// Adding a new JavaScript channel only takes affect after the next page is loaded.
	///
	/// Set values must not be null. A [JavascriptChannel.name] cannot be the same for multiple
	/// channels in the list.
	///
	/// A null value is equivalent to an empty set.
	final Set<JavascriptChannel> javascriptChannels;

	@override
	State<StatefulWidget> createState() => _WebViewState();
	}

	class _WebViewState extends State<WebView> {
	final Completer<WebViewController> _controller =
	Completer<WebViewController>();

	_WebSettings _settings;

	@override
	Widget build(BuildContext context) {
	if (defaultTargetPlatform == TargetPlatform.android) {
	return GestureDetector(
	// We prevent text selection by intercepting the long press event.
	// This is a temporary stop gap due to issues with text selection on Android:
	// https://github.com/flutter/flutter/issues/24585 - the text selection
	// dialog is not responding to touch events.
	// https://github.com/flutter/flutter/issues/24584 - the text selection
	// handles are not showing.
	// TODO(amirh): remove this when the issues above are fixed.
	onLongPress: () {},
	child: AndroidView(
	viewType: 'plugins.flutter.io/webview',
	onPlatformViewCreated: _onPlatformViewCreated,
	gestureRecognizers: widget.gestureRecognizers,
	// WebView content is not affected by the Android view's layout direction,
	// we explicitly set it here so that the widget doesn't require an ambient
	// directionality.
	layoutDirection: TextDirection.rtl,
	creationParams: _CreationParams.fromWidget(widget).toMap(),
	creationParamsCodec: const StandardMessageCodec(),
	),
	);
	} else if (defaultTargetPlatform == TargetPlatform.iOS) {
	return UiKitView(
	viewType: 'plugins.flutter.io/webview',
	onPlatformViewCreated: _onPlatformViewCreated,
	gestureRecognizers: widget.gestureRecognizers,
	creationParams: _CreationParams.fromWidget(widget).toMap(),
	creationParamsCodec: const StandardMessageCodec(),
	);
	}
	return Text(
	'$defaultTargetPlatform is not yet supported by the webview_flutter plugin');
	}

	@override
	void initState() {
	super.initState();
	_assertJavascriptChannelNamesAreUnique();
	}

	@override
	void didUpdateWidget(WebView oldWidget) {
	super.didUpdateWidget(oldWidget);
	_assertJavascriptChannelNamesAreUnique();
	_updateConfiguration(_WebSettings.fromWidget(widget));
	}

	Future<void> _updateConfiguration(_WebSettings settings) async {
	_settings = settings;
	final WebViewController controller = await _controller.future;
	controller._updateSettings(settings);
	controller._updateJavascriptChannels(widget.javascriptChannels);
	}

	void _onPlatformViewCreated(int id) {
	final WebViewController controller = WebViewController._(
	id,
	_WebSettings.fromWidget(widget),
	widget.javascriptChannels,
	);
	_controller.complete(controller);
	if (widget.onWebViewCreated != null) {
	widget.onWebViewCreated(controller);
	}
	}

	void _assertJavascriptChannelNamesAreUnique() {
	if (widget.javascriptChannels == null \|\|
	widget.javascriptChannels.isEmpty) {
	return;
	}
	assert(_extractChannelNames(widget.javascriptChannels).length ==
	widget.javascriptChannels.length);
	}
	}

	Set<String> _extractChannelNames(Set<JavascriptChannel> channels) {
	final Set<String> channelNames = channels == null
	? Set<String>()
	: channels.map((JavascriptChannel channel) => channel.name).toSet();
	return channelNames;
	}

	class _CreationParams {
	_CreationParams(
	{this.initialUrl, this.settings, this.javascriptChannelNames});

	static _CreationParams fromWidget(WebView widget) {
	return _CreationParams(
	initialUrl: widget.initialUrl,
	settings: _WebSettings.fromWidget(widget),
	javascriptChannelNames:
	_extractChannelNames(widget.javascriptChannels).toList(),
	);
	}

	final String initialUrl;

	final _WebSettings settings;

	final List<String> javascriptChannelNames;

	Map<String, dynamic> toMap() {
	return <String, dynamic>{
	'initialUrl': initialUrl,
	'settings': settings.toMap(),
	'javascriptChannelNames': javascriptChannelNames,
	};
	}
	}

	class _WebSettings {
	_WebSettings({
	this.javascriptMode,
	});

	static _WebSettings fromWidget(WebView widget) {
	return _WebSettings(javascriptMode: widget.javascriptMode);
	}

	final JavascriptMode javascriptMode;

	Map<String, dynamic> toMap() {
	return <String, dynamic>{
	'jsMode': javascriptMode.index,
	};
	}

	Map<String, dynamic> updatesMap(_WebSettings newSettings) {
	if (javascriptMode == newSettings.javascriptMode) {
	return null;
	}
	return <String, dynamic>{
	'jsMode': newSettings.javascriptMode.index,
	};
	}
	}

	/// Controls a [WebView].
	///
	/// A [WebViewController] instance can be obtained by setting the [WebView.onWebViewCreated]
	/// callback for a [WebView] widget.
	class WebViewController {
	WebViewController._(
	int id, this._settings, Set<JavascriptChannel> javascriptChannels)
	: _channel = MethodChannel('plugins.flutter.io/webview_$id') {
	_updateJavascriptChannelsFromSet(javascriptChannels);
	_channel.setMethodCallHandler(_onMethodCall);
	}

	final MethodChannel _channel;

	_WebSettings _settings;

	// Maps a channel name to a channel.
	Map<String, JavascriptChannel> _javascriptChannels =
	<String, JavascriptChannel>{};

	Future<void> _onMethodCall(MethodCall call) async {
	switch (call.method) {
	case 'javascriptChannelMessage':
	final String channel = call.arguments['channel'];
	final String message = call.arguments['message'];
	_javascriptChannels[channel]
	.onMessageReceived(JavascriptMessage(message));
	break;
	}
	}

	/// Loads the specified URL.
	///
	/// `url` must not be null.
	///
	/// Throws an ArgumentError if `url` is not a valid URL string.
	Future<void> loadUrl(String url) async {
	assert(url != null);
	_validateUrlString(url);
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	return _channel.invokeMethod('loadUrl', url);
	}

	/// Accessor to the current URL that the WebView is displaying.
	///
	/// If [WebView.initialUrl] was never specified, returns `null`.
	/// Note that this operation is asynchronous, and it is possible that the
	/// current URL changes again by the time this function returns (in other
	/// words, by the time this future completes, the WebView may be displaying a
	/// different URL).
	Future<String> currentUrl() async {
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	final String url = await _channel.invokeMethod('currentUrl');
	return url;
	}

	/// Checks whether there's a back history item.
	///
	/// Note that this operation is asynchronous, and it is possible that the "canGoBack" state has
	/// changed by the time the future completed.
	Future<bool> canGoBack() async {
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	final bool canGoBack = await _channel.invokeMethod("canGoBack");
	return canGoBack;
	}

	/// Checks whether there's a forward history item.
	///
	/// Note that this operation is asynchronous, and it is possible that the "canGoForward" state has
	/// changed by the time the future completed.
	Future<bool> canGoForward() async {
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	final bool canGoForward = await _channel.invokeMethod("canGoForward");
	return canGoForward;
	}

	/// Goes back in the history of this WebView.
	///
	/// If there is no back history item this is a no-op.
	Future<void> goBack() async {
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	return _channel.invokeMethod("goBack");
	}

	/// Goes forward in the history of this WebView.
	///
	/// If there is no forward history item this is a no-op.
	Future<void> goForward() async {
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	return _channel.invokeMethod("goForward");
	}

	/// Reloads the current URL.
	Future<void> reload() async {
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	return _channel.invokeMethod("reload");
	}

	Future<void> _updateSettings(_WebSettings setting) async {
	final Map<String, dynamic> updateMap = _settings.updatesMap(setting);
	if (updateMap == null) {
	return null;
	}
	_settings = setting;
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	return _channel.invokeMethod('updateSettings', updateMap);
	}

	Future<void> _updateJavascriptChannels(
	Set<JavascriptChannel> newChannels) async {
	final Set<String> currentChannels = _javascriptChannels.keys.toSet();
	final Set<String> newChannelNames = _extractChannelNames(newChannels);
	final Set<String> channelsToAdd =
	newChannelNames.difference(currentChannels);
	final Set<String> channelsToRemove =
	currentChannels.difference(newChannelNames);
	if (channelsToRemove.isNotEmpty) {
	// TODO(amirh): remove this when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	_channel.invokeMethod(
	'removeJavascriptChannels', channelsToRemove.toList());
	}
	if (channelsToAdd.isNotEmpty) {
	// TODO(amirh): remove this when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	_channel.invokeMethod('addJavascriptChannels', channelsToAdd.toList());
	}
	_updateJavascriptChannelsFromSet(newChannels);
	}

	void _updateJavascriptChannelsFromSet(Set<JavascriptChannel> channels) {
	_javascriptChannels.clear();
	if (channels == null) {
	return;
	}
	for (JavascriptChannel channel in channels) {
	_javascriptChannels[channel.name] = channel;
	}
	}

	/// Evaluates a JavaScript expression in the context of the current page.
	///
	/// On Android returns the evaluation result as a JSON formatted string.
	///
	/// On iOS depending on the value type the return value would be one of:
	///
	/// - For primitive JavaScript types: the value string formatted (e.g JavaScript 100 returns '100').
	/// - For JavaScript arrays of supported types: a string formatted NSArray(e.g '(1,2,3), note that the string for NSArray is formatted and might contain newlines and extra spaces.').
	/// - Other non-primitive types are not supported on iOS and will complete the Future with an error.
	///
	/// The Future completes with an error if a JavaScript error occurred, or on iOS, if the type of the
	/// evaluated expression is not supported as described above.
	Future<String> evaluateJavascript(String javascriptString) async {
	if (_settings.javascriptMode == JavascriptMode.disabled) {
	throw FlutterError(
	'JavaScript mode must be enabled/unrestricted when calling evaluateJavascript.');
	}
	if (javascriptString == null) {
	throw ArgumentError('The argument javascriptString must not be null. ');
	}
	// TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
	// https://github.com/flutter/flutter/issues/26431
	// ignore: strong_mode_implicit_dynamic_method
	final String result =
	await _channel.invokeMethod('evaluateJavascript', javascriptString);
	return result;
	}
	}

	// Throws an ArgumentError if `url` is not a valid URL string.
	void _validateUrlString(String url) {
	try {
	final Uri uri = Uri.parse(url);
	if (uri.scheme.isEmpty) {
	throw ArgumentError('Missing scheme in URL string: "$url"');
	}
	} on FormatException catch (e) {
	throw ArgumentError(e);
	}
	}