From 0e16deb085a91611f7290efc4ea2bea41deb828b Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Thu, 24 Jan 2019 16:06:14 -0800
Subject: [PATCH 01/11] Add WebView JavaScript channels (Dart side only).

---
 .../webview_flutter/lib/webview_flutter.dart  | 151 ++++++++++++++++--
 .../test/webview_flutter_test.dart            | 131 ++++++++++++---
 2 files changed, 252 insertions(+), 30 deletions(-)

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index 43f88b6892e4..ccc2a438df1c 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -19,6 +19,32 @@ enum JavascriptMode {
   unrestricted,
 }
 
+/// Callback type for handling messages sent from Javascript running in a web view.
+typedef void JavascriptMessageHandler(String message);
+
+/// 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,
+  });
+
+  /// 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`.
+  ///
+  /// 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.
@@ -32,6 +58,7 @@ class WebView extends StatefulWidget {
     this.onWebViewCreated,
     this.initialUrl,
     this.javascriptMode = JavascriptMode.disabled,
+    this.javascriptChannels,
     this.gestureRecognizers,
   })  : assert(javascriptMode != null),
         super(key: key);
@@ -56,13 +83,39 @@ class WebView extends StatefulWidget {
   /// 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.
+  ///
+  /// 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>();
+  final Completer<WebViewController> _controller = Completer<WebViewController>();
 
   _WebSettings _settings;
 
@@ -99,49 +152,78 @@ class _WebViewState extends State<WebView> {
         creationParamsCodec: const StandardMessageCodec(),
       );
     }
-    return Text(
-        '$defaultTargetPlatform is not yet supported by the webview_flutter plugin');
+    return Text('$defaultTargetPlatform is not yet supported by the webview_flutter plugin');
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    _assertJavascriptChannelNamesAreUnique();
   }
 
   @override
   void didUpdateWidget(WebView oldWidget) {
     super.didUpdateWidget(oldWidget);
-    _updateSettings(_WebSettings.fromWidget(widget));
+    _assertJavascriptChannelNamesAreUnique();
+    _updateConfiguration(_WebSettings.fromWidget(widget));
   }
 
-  Future<void> _updateSettings(_WebSettings settings) async {
+  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));
+    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});
+  _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,
     };
   }
 }
@@ -178,14 +260,29 @@ class _WebSettings {
 /// A [WebViewController] instance can be obtained by setting the [WebView.onWebViewCreated]
 /// callback for a [WebView] widget.
 class WebViewController {
-  WebViewController._(int id, _WebSettings settings)
-      : _channel = MethodChannel('plugins.flutter.io/webview_$id'),
-        _settings = settings;
+  WebViewController._(int id, this._settings, Set<JavascriptChannel> javascriptChannels)
+      : _channel = MethodChannel('plugins.flutter.io/webview_$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(message);
+        break;
+    }
+  }
+
   /// Loads the specified URL.
   ///
   /// `url` must not be null.
@@ -279,6 +376,36 @@ class WebViewController {
     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) {
+    if (channels == null) {
+      return;
+    }
+    _javascriptChannels.clear();
+    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.
diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index ae286bf5118e..ccd9546f6aba 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -10,12 +10,11 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 
 void main() {
-  final _FakePlatformViewsController fakePlatformViewsController =
-      _FakePlatformViewsController();
+  final _FakePlatformViewsController fakePlatformViewsController = _FakePlatformViewsController();
 
   setUpAll(() {
-    SystemChannels.platform_views.setMockMethodCallHandler(
-        fakePlatformViewsController.fakePlatformViewsMethodHandler);
+    SystemChannels.platform_views
+        .setMockMethodCallHandler(fakePlatformViewsController.fakePlatformViewsMethodHandler);
   });
 
   setUp(() {
@@ -46,8 +45,7 @@ void main() {
       javascriptMode: JavascriptMode.unrestricted,
     ));
 
-    final FakePlatformWebView platformWebView =
-        fakePlatformViewsController.lastCreatedView;
+    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
 
     expect(platformWebView.javascriptMode, JavascriptMode.unrestricted);
 
@@ -99,8 +97,7 @@ void main() {
     expect(await controller.currentUrl(), isNull);
   });
 
-  testWidgets("Can't go back before loading a page",
-      (WidgetTester tester) async {
+  testWidgets("Can't go back before loading a page", (WidgetTester tester) async {
     WebViewController controller;
     await tester.pumpWidget(
       WebView(
@@ -153,8 +150,7 @@ void main() {
     expect(canGoBackSecondPageLoaded, true);
   });
 
-  testWidgets("Can't go forward before loading a page",
-      (WidgetTester tester) async {
+  testWidgets("Can't go forward before loading a page", (WidgetTester tester) async {
     WebViewController controller;
     await tester.pumpWidget(
       WebView(
@@ -296,8 +292,7 @@ void main() {
       ),
     );
 
-    final FakePlatformWebView platformWebView =
-        fakePlatformViewsController.lastCreatedView;
+    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
 
     expect(platformWebView.currentUrl, 'https://flutter.io');
     expect(platformWebView.amountOfReloadsOnCurrentUrl, 0);
@@ -323,8 +318,7 @@ void main() {
         },
       ),
     );
-    expect(
-        await controller.evaluateJavascript("fake js string"), "fake js string",
+    expect(await controller.evaluateJavascript("fake js string"), "fake js string",
         reason: 'should get the argument');
     expect(
       () => controller.evaluateJavascript(null),
@@ -332,8 +326,7 @@ void main() {
     );
   });
 
-  testWidgets('evaluate Javascript with JavascriptMode disabled',
-      (WidgetTester tester) async {
+  testWidgets('evaluate Javascript with JavascriptMode disabled', (WidgetTester tester) async {
     WebViewController controller;
     await tester.pumpWidget(
       WebView(
@@ -353,6 +346,86 @@ void main() {
       throwsA(anything),
     );
   });
+
+  testWidgets('Initial JavaScript channels', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptChannels: <JavascriptChannel>[
+          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
+        ].toSet(),
+      ),
+    );
+
+    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+
+    expect(platformWebView.javascriptChannelNames, unorderedEquals(<String>['Tts', 'Alarm']));
+  });
+
+  testWidgets('Unique JavaScript channel names are required', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptChannels: <JavascriptChannel>[
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
+        ].toSet(),
+      ),
+    );
+    expect(tester.takeException(), isNot(null));
+  });
+
+  testWidgets('JavaScript channels update', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptChannels: <JavascriptChannel>[
+          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
+        ].toSet(),
+      ),
+    );
+
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptChannels: <JavascriptChannel>[
+          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Alarm2', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Alarm3', onMessageReceived: (String msg) {}),
+        ].toSet(),
+      ),
+    );
+
+    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+
+    expect(platformWebView.javascriptChannelNames, unorderedEquals(<String>['Tts', 'Alarm2', 'Alarm3']));
+  });
+
+  testWidgets('JavaScript channel messages', (WidgetTester tester) async {
+    final List<String> ttsMessagesReceived = <String>[];
+    final List<String> alarmMessagesReceived = <String>[];
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptChannels: <JavascriptChannel>[
+          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {ttsMessagesReceived.add(msg); }),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {alarmMessagesReceived.add(msg); }),
+        ].toSet(),
+      ),
+    );
+
+    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+
+    expect(ttsMessagesReceived, isEmpty);
+    expect(alarmMessagesReceived, isEmpty);
+
+    platformWebView.fakeJavascriptPostMessage('Tts', 'Hello');
+    platformWebView.fakeJavascriptPostMessage('Tts', 'World');
+
+    expect(ttsMessagesReceived, <String>['Hello', 'World']);
+  });
 }
 
 class FakePlatformWebView {
@@ -365,8 +438,10 @@ class FakePlatformWebView {
       }
       javascriptMode = JavascriptMode.values[params['settings']['jsMode']];
     }
-    channel = MethodChannel(
-        'plugins.flutter.io/webview_$id', const StandardMethodCodec());
+    if (params.containsKey('javascriptChannelNames')) {
+      javascriptChannelNames = List<String>.from(params['javascriptChannelNames']);
+    }
+    channel = MethodChannel('plugins.flutter.io/webview_$id', const StandardMethodCodec());
     channel.setMockMethodCallHandler(onMethodCall);
   }
 
@@ -378,6 +453,7 @@ class FakePlatformWebView {
 
   String get currentUrl => history.isEmpty ? null : history[currentPosition];
   JavascriptMode javascriptMode;
+  List<String> javascriptChannelNames;
 
   Future<dynamic> onMethodCall(MethodCall call) {
     switch (call.method) {
@@ -416,9 +492,28 @@ class FakePlatformWebView {
         break;
       case 'evaluateJavascript':
         return Future<dynamic>.value(call.arguments);
+        break;
+      case 'addJavascriptChannels':
+        final List<String> channelNames = List<String>.from(call.arguments);
+        javascriptChannelNames.addAll(channelNames);
+        break;
+      case 'removeJavascriptChannels':
+        final List<String> channelNames = List<String>.from(call.arguments);
+        javascriptChannelNames.removeWhere((String channel) => channelNames.contains(channel));
+        break;
     }
     return Future<void>.sync(() {});
   }
+
+  void fakeJavascriptPostMessage(String jsChannel, String message) {
+    final StandardMethodCodec codec = const StandardMethodCodec();
+    final Map<String, dynamic> arguments = <String, dynamic> {
+      'channel': jsChannel,
+      'message': message
+    };
+    final ByteData data = codec.encodeMethodCall(MethodCall('javascriptChannelMessage', arguments));
+    BinaryMessages.handlePlatformMessage(channel.name, data, (ByteData data) {});
+  }
 }
 
 class _FakePlatformViewsController {

From 015f025a24a1b39220434f6e38e92e923d62e3ce Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Fri, 25 Jan 2019 13:29:23 -0800
Subject: [PATCH 02/11] format

---
 .../webview_flutter/lib/webview_flutter.dart  | 38 ++++++----
 .../test/webview_flutter_test.dart            | 72 +++++++++++++------
 2 files changed, 74 insertions(+), 36 deletions(-)

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index ccc2a438df1c..4ec173793618 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -115,7 +115,8 @@ class WebView extends StatefulWidget {
 }
 
 class _WebViewState extends State<WebView> {
-  final Completer<WebViewController> _controller = Completer<WebViewController>();
+  final Completer<WebViewController> _controller =
+      Completer<WebViewController>();
 
   _WebSettings _settings;
 
@@ -152,7 +153,8 @@ class _WebViewState extends State<WebView> {
         creationParamsCodec: const StandardMessageCodec(),
       );
     }
-    return Text('$defaultTargetPlatform is not yet supported by the webview_flutter plugin');
+    return Text(
+        '$defaultTargetPlatform is not yet supported by the webview_flutter plugin');
   }
 
   @override
@@ -188,10 +190,12 @@ class _WebViewState extends State<WebView> {
   }
 
   void _assertJavascriptChannelNamesAreUnique() {
-    if (widget.javascriptChannels == null || widget.javascriptChannels.isEmpty) {
+    if (widget.javascriptChannels == null ||
+        widget.javascriptChannels.isEmpty) {
       return;
     }
-    assert(_extractChannelNames(widget.javascriptChannels).length == widget.javascriptChannels.length);
+    assert(_extractChannelNames(widget.javascriptChannels).length ==
+        widget.javascriptChannels.length);
   }
 }
 
@@ -203,13 +207,15 @@ Set<String> _extractChannelNames(Set<JavascriptChannel> channels) {
 }
 
 class _CreationParams {
-  _CreationParams({this.initialUrl, this.settings, this.javascriptChannelNames});
+  _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(),
+      javascriptChannelNames:
+          _extractChannelNames(widget.javascriptChannels).toList(),
     );
   }
 
@@ -260,7 +266,8 @@ class _WebSettings {
 /// 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)
+  WebViewController._(
+      int id, this._settings, Set<JavascriptChannel> javascriptChannels)
       : _channel = MethodChannel('plugins.flutter.io/webview_$id') {
     _updateJavascriptChannelsFromSet(javascriptChannels);
     _channel.setMethodCallHandler(_onMethodCall);
@@ -271,10 +278,11 @@ class WebViewController {
   _WebSettings _settings;
 
   // Maps a channel name to a channel.
-  Map<String, JavascriptChannel> _javascriptChannels = <String, JavascriptChannel> {};
+  Map<String, JavascriptChannel> _javascriptChannels =
+      <String, JavascriptChannel>{};
 
   Future<void> _onMethodCall(MethodCall call) async {
-    switch(call.method) {
+    switch (call.method) {
       case 'javascriptChannelMessage':
         final String channel = call.arguments['channel'];
         final String message = call.arguments['message'];
@@ -376,16 +384,20 @@ class WebViewController {
     return _channel.invokeMethod('updateSettings', updateMap);
   }
 
-  Future<void> _updateJavascriptChannels(Set<JavascriptChannel> newChannels) async {
+  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);
+    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());
+      _channel.invokeMethod(
+          'removeJavascriptChannels', channelsToRemove.toList());
     }
     if (channelsToAdd.isNotEmpty) {
       // TODO(amirh): remove this when the invokeMethod update makes it to stable Flutter.
diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index ccd9546f6aba..f87517a04582 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -10,11 +10,12 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 
 void main() {
-  final _FakePlatformViewsController fakePlatformViewsController = _FakePlatformViewsController();
+  final _FakePlatformViewsController fakePlatformViewsController =
+      _FakePlatformViewsController();
 
   setUpAll(() {
-    SystemChannels.platform_views
-        .setMockMethodCallHandler(fakePlatformViewsController.fakePlatformViewsMethodHandler);
+    SystemChannels.platform_views.setMockMethodCallHandler(
+        fakePlatformViewsController.fakePlatformViewsMethodHandler);
   });
 
   setUp(() {
@@ -45,7 +46,8 @@ void main() {
       javascriptMode: JavascriptMode.unrestricted,
     ));
 
-    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+    final FakePlatformWebView platformWebView =
+        fakePlatformViewsController.lastCreatedView;
 
     expect(platformWebView.javascriptMode, JavascriptMode.unrestricted);
 
@@ -97,7 +99,8 @@ void main() {
     expect(await controller.currentUrl(), isNull);
   });
 
-  testWidgets("Can't go back before loading a page", (WidgetTester tester) async {
+  testWidgets("Can't go back before loading a page",
+      (WidgetTester tester) async {
     WebViewController controller;
     await tester.pumpWidget(
       WebView(
@@ -150,7 +153,8 @@ void main() {
     expect(canGoBackSecondPageLoaded, true);
   });
 
-  testWidgets("Can't go forward before loading a page", (WidgetTester tester) async {
+  testWidgets("Can't go forward before loading a page",
+      (WidgetTester tester) async {
     WebViewController controller;
     await tester.pumpWidget(
       WebView(
@@ -292,7 +296,8 @@ void main() {
       ),
     );
 
-    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+    final FakePlatformWebView platformWebView =
+        fakePlatformViewsController.lastCreatedView;
 
     expect(platformWebView.currentUrl, 'https://flutter.io');
     expect(platformWebView.amountOfReloadsOnCurrentUrl, 0);
@@ -318,7 +323,8 @@ void main() {
         },
       ),
     );
-    expect(await controller.evaluateJavascript("fake js string"), "fake js string",
+    expect(
+        await controller.evaluateJavascript("fake js string"), "fake js string",
         reason: 'should get the argument');
     expect(
       () => controller.evaluateJavascript(null),
@@ -326,7 +332,8 @@ void main() {
     );
   });
 
-  testWidgets('evaluate Javascript with JavascriptMode disabled', (WidgetTester tester) async {
+  testWidgets('evaluate Javascript with JavascriptMode disabled',
+      (WidgetTester tester) async {
     WebViewController controller;
     await tester.pumpWidget(
       WebView(
@@ -358,12 +365,15 @@ void main() {
       ),
     );
 
-    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+    final FakePlatformWebView platformWebView =
+        fakePlatformViewsController.lastCreatedView;
 
-    expect(platformWebView.javascriptChannelNames, unorderedEquals(<String>['Tts', 'Alarm']));
+    expect(platformWebView.javascriptChannelNames,
+        unorderedEquals(<String>['Tts', 'Alarm']));
   });
 
-  testWidgets('Unique JavaScript channel names are required', (WidgetTester tester) async {
+  testWidgets('Unique JavaScript channel names are required',
+      (WidgetTester tester) async {
     await tester.pumpWidget(
       WebView(
         initialUrl: 'https://youtube.com',
@@ -398,9 +408,11 @@ void main() {
       ),
     );
 
-    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+    final FakePlatformWebView platformWebView =
+        fakePlatformViewsController.lastCreatedView;
 
-    expect(platformWebView.javascriptChannelNames, unorderedEquals(<String>['Tts', 'Alarm2', 'Alarm3']));
+    expect(platformWebView.javascriptChannelNames,
+        unorderedEquals(<String>['Tts', 'Alarm2', 'Alarm3']));
   });
 
   testWidgets('JavaScript channel messages', (WidgetTester tester) async {
@@ -410,13 +422,22 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {ttsMessagesReceived.add(msg); }),
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {alarmMessagesReceived.add(msg); }),
+          JavascriptChannel(
+              name: 'Tts',
+              onMessageReceived: (String msg) {
+                ttsMessagesReceived.add(msg);
+              }),
+          JavascriptChannel(
+              name: 'Alarm',
+              onMessageReceived: (String msg) {
+                alarmMessagesReceived.add(msg);
+              }),
         ].toSet(),
       ),
     );
 
-    final FakePlatformWebView platformWebView = fakePlatformViewsController.lastCreatedView;
+    final FakePlatformWebView platformWebView =
+        fakePlatformViewsController.lastCreatedView;
 
     expect(ttsMessagesReceived, isEmpty);
     expect(alarmMessagesReceived, isEmpty);
@@ -439,9 +460,11 @@ class FakePlatformWebView {
       javascriptMode = JavascriptMode.values[params['settings']['jsMode']];
     }
     if (params.containsKey('javascriptChannelNames')) {
-      javascriptChannelNames = List<String>.from(params['javascriptChannelNames']);
+      javascriptChannelNames =
+          List<String>.from(params['javascriptChannelNames']);
     }
-    channel = MethodChannel('plugins.flutter.io/webview_$id', const StandardMethodCodec());
+    channel = MethodChannel(
+        'plugins.flutter.io/webview_$id', const StandardMethodCodec());
     channel.setMockMethodCallHandler(onMethodCall);
   }
 
@@ -499,7 +522,8 @@ class FakePlatformWebView {
         break;
       case 'removeJavascriptChannels':
         final List<String> channelNames = List<String>.from(call.arguments);
-        javascriptChannelNames.removeWhere((String channel) => channelNames.contains(channel));
+        javascriptChannelNames
+            .removeWhere((String channel) => channelNames.contains(channel));
         break;
     }
     return Future<void>.sync(() {});
@@ -507,12 +531,14 @@ class FakePlatformWebView {
 
   void fakeJavascriptPostMessage(String jsChannel, String message) {
     final StandardMethodCodec codec = const StandardMethodCodec();
-    final Map<String, dynamic> arguments = <String, dynamic> {
+    final Map<String, dynamic> arguments = <String, dynamic>{
       'channel': jsChannel,
       'message': message
     };
-    final ByteData data = codec.encodeMethodCall(MethodCall('javascriptChannelMessage', arguments));
-    BinaryMessages.handlePlatformMessage(channel.name, data, (ByteData data) {});
+    final ByteData data = codec
+        .encodeMethodCall(MethodCall('javascriptChannelMessage', arguments));
+    BinaryMessages.handlePlatformMessage(
+        channel.name, data, (ByteData data) {});
   }
 }
 

From 452a45c17a72ee368640a0c2d76357cafe469164 Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Mon, 28 Jan 2019 08:59:56 -0800
Subject: [PATCH 03/11] Enforce channel names

---
 .../webview_flutter/lib/webview_flutter.dart   | 10 ++++++++--
 .../test/webview_flutter_test.dart             | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index 4ec173793618..0bea7de00c7f 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -22,6 +22,8 @@ enum JavascriptMode {
 /// Callback type for handling messages sent from Javascript running in a web view.
 typedef void JavascriptMessageHandler(String 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.
@@ -30,14 +32,18 @@ class JavascriptChannel {
   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.
+  ///
   /// See also [WebView.javascriptChannels] for more details on the channel registration mechanism.
   final String name;
 
diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index f87517a04582..0f3c2fdd690f 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -9,6 +9,8 @@ import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 
+typedef void VoidCallback();
+
 void main() {
   final _FakePlatformViewsController fakePlatformViewsController =
       _FakePlatformViewsController();
@@ -372,6 +374,22 @@ void main() {
         unorderedEquals(<String>['Tts', 'Alarm']));
   });
 
+  test('Only valid JavaScript channel names are allowed', () {
+    final JavascriptMessageHandler noOp = (String msg) {};
+    JavascriptChannel(name: 'Tts1', onMessageReceived: noOp);
+    JavascriptChannel(name: '_Alarm', onMessageReceived: noOp);
+
+    VoidCallback createChannel(String name) {
+      return () {
+        JavascriptChannel(name: name, onMessageReceived: noOp);
+      };
+    }
+
+    expect(createChannel('1Alarm'), throwsAssertionError);
+    expect(createChannel('foo.bar'), throwsAssertionError);
+    expect(createChannel(''), throwsAssertionError);
+  });
+
   testWidgets('Unique JavaScript channel names are required',
       (WidgetTester tester) async {
     await tester.pumpWidget(

From 1699836e939b6365e50b28a25aa72f8d84f4c457 Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Mon, 28 Jan 2019 15:31:27 -0800
Subject: [PATCH 04/11] Pass messages as JavascriptMessage objects. Add a note
 about overriding window properties.

---
 .../webview_flutter/lib/webview_flutter.dart  | 17 +++++++++--
 .../test/webview_flutter_test.dart            | 28 +++++++++----------
 2 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index 0bea7de00c7f..75335a01bb59 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -19,8 +19,19 @@ enum JavascriptMode {
   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(String message);
+typedef void JavascriptMessageHandler(JavascriptMessage message);
 
 final RegExp _validChannelNames = RegExp('^[a-zA-Z_][a-zA-Z0-9]*\$');
 
@@ -44,6 +55,8 @@ class JavascriptChannel {
   /// 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;
 
@@ -292,7 +305,7 @@ class WebViewController {
       case 'javascriptChannelMessage':
         final String channel = call.arguments['channel'];
         final String message = call.arguments['message'];
-        _javascriptChannels[channel].onMessageReceived(message);
+        _javascriptChannels[channel].onMessageReceived(JavascriptMessage(message));
         break;
     }
   }
diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index 0f3c2fdd690f..8b459d48c3f0 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -361,8 +361,8 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {}),
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -375,7 +375,7 @@ void main() {
   });
 
   test('Only valid JavaScript channel names are allowed', () {
-    final JavascriptMessageHandler noOp = (String msg) {};
+    final JavascriptMessageHandler noOp = (JavascriptMessage msg) {};
     JavascriptChannel(name: 'Tts1', onMessageReceived: noOp);
     JavascriptChannel(name: '_Alarm', onMessageReceived: noOp);
 
@@ -396,8 +396,8 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -409,8 +409,8 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {}),
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -419,9 +419,9 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (String msg) {}),
-          JavascriptChannel(name: 'Alarm2', onMessageReceived: (String msg) {}),
-          JavascriptChannel(name: 'Alarm3', onMessageReceived: (String msg) {}),
+          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(name: 'Alarm2', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(name: 'Alarm3', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -442,13 +442,13 @@ void main() {
         javascriptChannels: <JavascriptChannel>[
           JavascriptChannel(
               name: 'Tts',
-              onMessageReceived: (String msg) {
-                ttsMessagesReceived.add(msg);
+              onMessageReceived: (JavascriptMessage msg) {
+                ttsMessagesReceived.add(msg.message);
               }),
           JavascriptChannel(
               name: 'Alarm',
-              onMessageReceived: (String msg) {
-                alarmMessagesReceived.add(msg);
+              onMessageReceived: (JavascriptMessage msg) {
+                alarmMessagesReceived.add(msg.message);
               }),
         ].toSet(),
       ),

From 83be1fada4e164109cd8e9bf6809864496db22ef Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Mon, 28 Jan 2019 15:36:17 -0800
Subject: [PATCH 05/11] format

---
 .../webview_flutter/lib/webview_flutter.dart  |  3 ++-
 .../test/webview_flutter_test.dart            | 27 ++++++++++++-------
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index 75335a01bb59..c1afeabb2963 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -305,7 +305,8 @@ class WebViewController {
       case 'javascriptChannelMessage':
         final String channel = call.arguments['channel'];
         final String message = call.arguments['message'];
-        _javascriptChannels[channel].onMessageReceived(JavascriptMessage(message));
+        _javascriptChannels[channel]
+            .onMessageReceived(JavascriptMessage(message));
         break;
     }
   }
diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index 8b459d48c3f0..f7eb07b32370 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -361,8 +361,10 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -396,8 +398,10 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -409,8 +413,10 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
-          JavascriptChannel(name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Alarm', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -419,9 +425,12 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
-          JavascriptChannel(name: 'Alarm2', onMessageReceived: (JavascriptMessage msg) {}),
-          JavascriptChannel(name: 'Alarm3', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Alarm2', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Alarm3', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );

From 2c423dd38e848f0324927b88c74fe64cdb589af2 Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Mon, 28 Jan 2019 16:02:21 -0800
Subject: [PATCH 06/11] fix channel cache update cache bug

---
 .../webview_flutter/lib/webview_flutter.dart  |  2 +-
 .../test/webview_flutter_test.dart            | 37 +++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index c1afeabb2963..77c8f56c0546 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -429,10 +429,10 @@ class WebViewController {
   }
 
   void _updateJavascriptChannelsFromSet(Set<JavascriptChannel> channels) {
+    _javascriptChannels.clear();
     if (channels == null) {
       return;
     }
-    _javascriptChannels.clear();
     for (JavascriptChannel channel in channels) {
       _javascriptChannels[channel.name] = channel;
     }
diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index f7eb07b32370..05c5c497468d 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -442,6 +442,42 @@ void main() {
         unorderedEquals(<String>['Tts', 'Alarm2', 'Alarm3']));
   });
 
+  testWidgets('Remove all JavaScript channels and then add', (WidgetTester tester) async {
+    // This covers a specific bug we had where after updating javascriptChannels to null,
+    // updating it again with a subset of the previously registered channels fails as the
+    // widget's cache of current channel wasn't properly updated when updating javascriptChannels to
+    // null.
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptChannels: <JavascriptChannel>[
+          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+        ].toSet(),
+      ),
+    );
+
+    await tester.pumpWidget(
+      const WebView(
+        initialUrl: 'https://youtube.com',
+      ),
+    );
+
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptChannels: <JavascriptChannel>[
+          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+        ].toSet(),
+      ),
+    );
+
+    final FakePlatformWebView platformWebView =
+        fakePlatformViewsController.lastCreatedView;
+
+    expect(platformWebView.javascriptChannelNames,
+        unorderedEquals(<String>['Tts']));
+  });
+
   testWidgets('JavaScript channel messages', (WidgetTester tester) async {
     final List<String> ttsMessagesReceived = <String>[];
     final List<String> alarmMessagesReceived = <String>[];
@@ -474,6 +510,7 @@ void main() {
 
     expect(ttsMessagesReceived, <String>['Hello', 'World']);
   });
+
 }
 
 class FakePlatformWebView {

From 57b3cd5c8da9d3923f6b8f98330753d443b6d49c Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Mon, 28 Jan 2019 16:32:15 -0800
Subject: [PATCH 07/11] format with stable flutter

---
 .../webview_flutter/test/webview_flutter_test.dart     | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index 05c5c497468d..12b4831b5399 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -442,7 +442,8 @@ void main() {
         unorderedEquals(<String>['Tts', 'Alarm2', 'Alarm3']));
   });
 
-  testWidgets('Remove all JavaScript channels and then add', (WidgetTester tester) async {
+  testWidgets('Remove all JavaScript channels and then add',
+      (WidgetTester tester) async {
     // This covers a specific bug we had where after updating javascriptChannels to null,
     // updating it again with a subset of the previously registered channels fails as the
     // widget's cache of current channel wasn't properly updated when updating javascriptChannels to
@@ -451,7 +452,8 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -466,7 +468,8 @@ void main() {
       WebView(
         initialUrl: 'https://youtube.com',
         javascriptChannels: <JavascriptChannel>[
-          JavascriptChannel(name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
+          JavascriptChannel(
+              name: 'Tts', onMessageReceived: (JavascriptMessage msg) {}),
         ].toSet(),
       ),
     );
@@ -510,7 +513,6 @@ void main() {
 
     expect(ttsMessagesReceived, <String>['Hello', 'World']);
   });
-
 }
 
 class FakePlatformWebView {

From b57117f6697fc995d8a195938adfc22664fa53d2 Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Wed, 30 Jan 2019 16:23:21 -0800
Subject: [PATCH 08/11] Document when adding a channel takes affect.

---
 packages/webview_flutter/lib/webview_flutter.dart | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index 77c8f56c0546..8d5a74686760 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -123,6 +123,8 @@ class WebView extends StatefulWidget {
   ///
   /// 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.
   ///

From 59e12482fedbef73b0a67dfdefb6a4652ee61a16 Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Wed, 30 Jan 2019 16:23:42 -0800
Subject: [PATCH 09/11] update changelog and bump version

---
 packages/webview_flutter/CHANGELOG.md | 5 +++++
 packages/webview_flutter/pubspec.yaml | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/packages/webview_flutter/CHANGELOG.md b/packages/webview_flutter/CHANGELOG.md
index d90be52c5468..07a69c0f3501 100644
--- a/packages/webview_flutter/CHANGELOG.md
+++ b/packages/webview_flutter/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 0.3.1
+
+* Added JavaScript channels to facilitate message passing from JavaScript code running inside
+  the WebView to the Flutter app's Dart code.
+
 ## 0.3.0
 
 * **Breaking change**. Migrate from the deprecated original Android Support
diff --git a/packages/webview_flutter/pubspec.yaml b/packages/webview_flutter/pubspec.yaml
index 2ed52c97e23a..329159e0eeab 100644
--- a/packages/webview_flutter/pubspec.yaml
+++ b/packages/webview_flutter/pubspec.yaml
@@ -1,6 +1,6 @@
 name: webview_flutter
 description: A Flutter plugin that provides a WebView widget on Android and iOS.
-version: 0.3.0
+version: 0.3.1
 author: Flutter Team <flutter-dev@googlegroups.com>
 homepage: https://github.com/flutter/plugins/tree/master/packages/webview_flutter
 

From 9a350dd179fe550ada3820cd47f13c64f912d4c0 Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Wed, 30 Jan 2019 16:46:41 -0800
Subject: [PATCH 10/11] Use JavascriptChannels in the example app

---
 .../webview_flutter/example/lib/main.dart     | 56 ++++++++++++-------
 1 file changed, 35 insertions(+), 21 deletions(-)

diff --git a/packages/webview_flutter/example/lib/main.dart b/packages/webview_flutter/example/lib/main.dart
index 9befe4b67f41..fcb80bbfaf21 100644
--- a/packages/webview_flutter/example/lib/main.dart
+++ b/packages/webview_flutter/example/lib/main.dart
@@ -23,17 +23,34 @@ class WebViewExample extends StatelessWidget {
           SampleMenu(_controller.future),
         ],
       ),
-      body: WebView(
-        initialUrl: 'https://flutter.io',
-        javascriptMode: JavascriptMode.unrestricted,
-        onWebViewCreated: (WebViewController webViewController) {
-          _controller.complete(webViewController);
-        },
-      ),
+      // We're using a Builder here so we have a context that is below the Scaffold
+      // to allow calling Scaffold.maketoast
+      body: Builder(builder: (BuildContext context) {
+        return WebView(
+          initialUrl: 'https://flutter.io',
+          javascriptMode: JavascriptMode.unrestricted,
+          onWebViewCreated: (WebViewController webViewController) {
+            _controller.complete(webViewController);
+          },
+          javascriptChannels: <JavascriptChannel>[
+            _toasterJavascriptChannel(context),
+          ].toSet(),
+        );
+      }),
       floatingActionButton: favoriteButton(),
     );
   }
 
+  JavascriptChannel _toasterJavascriptChannel(BuildContext context) {
+    return JavascriptChannel(
+        name: 'Toaster',
+        onMessageReceived: (JavascriptMessage message) {
+          Scaffold.of(context).showSnackBar(
+            SnackBar(content: Text(message.message)),
+          );
+        });
+  }
+
   Widget favoriteButton() {
     return FutureBuilder<WebViewController>(
         future: _controller.future,
@@ -44,7 +61,7 @@ class WebViewExample extends StatelessWidget {
               onPressed: () async {
                 final String url = await controller.data.currentUrl();
                 Scaffold.of(context).showSnackBar(
-                  SnackBar(content: Text("Favorited $url")),
+                  SnackBar(content: Text('Favorited $url')),
                 );
               },
               child: const Icon(Icons.favorite),
@@ -56,7 +73,7 @@ class WebViewExample extends StatelessWidget {
 }
 
 enum MenuOptions {
-  evaluateJavascript,
+  showUserAgent,
   toast,
 }
 
@@ -73,8 +90,8 @@ class SampleMenu extends StatelessWidget {
         return PopupMenuButton<MenuOptions>(
           onSelected: (MenuOptions value) {
             switch (value) {
-              case MenuOptions.evaluateJavascript:
-                _onEvaluateJavascript(controller.data, context);
+              case MenuOptions.showUserAgent:
+                _onShowUserAgent(controller.data, context);
                 break;
               case MenuOptions.toast:
                 Scaffold.of(context).showSnackBar(
@@ -87,8 +104,8 @@ class SampleMenu extends StatelessWidget {
           },
           itemBuilder: (BuildContext context) => <PopupMenuItem<MenuOptions>>[
                 PopupMenuItem<MenuOptions>(
-                  value: MenuOptions.evaluateJavascript,
-                  child: const Text('Evaluate JavaScript'),
+                  value: MenuOptions.showUserAgent,
+                  child: const Text('Show user agent'),
                   enabled: controller.hasData,
                 ),
                 const PopupMenuItem<MenuOptions>(
@@ -101,15 +118,12 @@ class SampleMenu extends StatelessWidget {
     );
   }
 
-  void _onEvaluateJavascript(
+  void _onShowUserAgent(
       WebViewController controller, BuildContext context) async {
-    final String result = await controller
-        .evaluateJavascript("document.body.style.backgroundColor = 'red'");
-    Scaffold.of(context).showSnackBar(
-      SnackBar(
-        content: Text('JavaScript evaluated, the result is: $result'),
-      ),
-    );
+    // Send a message with the user agent string to the Toaster JavaScript channel we registered
+    // with the WebView.
+    controller.evaluateJavascript(
+        'Toaster.postMessage("User Agent: " + navigator.userAgent);');
   }
 }
 

From 61807a170a7cd43e7de3ace01ba1804783cd5fdf Mon Sep 17 00:00:00 2001
From: Amir Hardon <amirha@google.com>
Date: Mon, 4 Feb 2019 11:35:53 -0800
Subject: [PATCH 11/11] fix example comment

---
 packages/webview_flutter/example/lib/main.dart | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/webview_flutter/example/lib/main.dart b/packages/webview_flutter/example/lib/main.dart
index fcb80bbfaf21..d8a4e8c439d8 100644
--- a/packages/webview_flutter/example/lib/main.dart
+++ b/packages/webview_flutter/example/lib/main.dart
@@ -24,7 +24,7 @@ class WebViewExample extends StatelessWidget {
         ],
       ),
       // We're using a Builder here so we have a context that is below the Scaffold
-      // to allow calling Scaffold.maketoast
+      // to allow calling Scaffold.of(context) so we can show a snackbar.
       body: Builder(builder: (BuildContext context) {
         return WebView(
           initialUrl: 'https://flutter.io',