[webview_flutter]Support UserAgent setting for webview_flutter

packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/FlutterWebView.java

@@ -63,6 +63,9 @@ public void onMethodCall(MethodCall methodCall, Result result) {
       case "loadUrl":
         loadUrl(methodCall, result);
         break;
+      case "getUserAgent":
+        getUserAgent(methodCall, result);
+        break;
       case "updateSettings":
         updateSettings(methodCall, result);
         break;
@@ -144,6 +147,11 @@ private void currentUrl(Result result) {
     result.success(webView.getUrl());
   }
 
+  private void getUserAgent(MethodCall methodCall, Result result) {
+    String userAgent = webView.getSettings().getUserAgentString();
+    result.success(userAgent);
+  }
+
   @SuppressWarnings("unchecked")
   private void updateSettings(MethodCall methodCall, Result result) {
     applySettings((Map<String, Object>) methodCall.arguments);
@@ -207,6 +215,9 @@ private void applySettings(Map<String, Object> settings) {
 
           webView.setWebContentsDebuggingEnabled(debuggingEnabled);
           break;
+        case "userAgent":
+          updateUserAgent((String) settings.get(key));
+          break;
         default:
           throw new IllegalArgumentException("Unknown WebView setting: " + key);
       }
@@ -233,6 +244,10 @@ private void registerJavaScriptChannelNames(List<String> channelNames) {
     }
   }
 
+  private void updateUserAgent(String userAgent) {
+    webView.getSettings().setUserAgentString(userAgent);
+  }
+
   @Override
   public void dispose() {
     methodChannel.setMethodCallHandler(null);

packages/webview_flutter/example/test_driver/webview.dart

@@ -132,6 +132,49 @@ void main() {
     await controller.evaluateJavascript('Echo.postMessage("hello");');
     expect(messagesReceived, equals(<String>['hello']));
   });
+
+  test('userAgent', () async {
+    final Completer<WebViewController> controllerCompleter01 =
+        Completer<WebViewController>();
+    await pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: WebView(
+          key: GlobalKey(),
+          initialUrl: 'https://flutter.dev/',
+          javascriptMode: JavascriptMode.unrestricted,
+          userAgent: 'UA-01',
+          onWebViewCreated: (WebViewController controller) {
+            controllerCompleter01.complete(controller);
+          },
+        ),
+      ),
+    );
+    final WebViewController controller01 = await controllerCompleter01.future;
+    final String userAgent01 = await controller01.getUserAgent();
+    expect(userAgent01, 'UA-01');
+
+    // rebuilds a WebView with a different user agent.
+    final Completer<WebViewController> controllerCompleter02 =
+        Completer<WebViewController>();
+    await pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: WebView(
+          key: GlobalKey(),
+          initialUrl: 'https://flutter.dev/',
+          javascriptMode: JavascriptMode.unrestricted,
+          userAgent: 'UA-02',
+          onWebViewCreated: (WebViewController controller) {
+            controllerCompleter02.complete(controller);
+          },
+        ),
+      ),
+    );
+    final WebViewController controller02 = await controllerCompleter02.future;
+    final String userAgent02 = await controller02.getUserAgent();
+    expect(userAgent02, 'UA-02');
+  });
 }
 
 Future<void> pumpWidget(Widget widget) {

packages/webview_flutter/ios/Classes/FlutterWebView.m

@@ -112,6 +112,8 @@ - (void)onMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
     [self onRemoveJavaScriptChannels:call result:result];
   } else if ([[call method] isEqualToString:@"clearCache"]) {
     [self clearCache:result];
+  } else if ([[call method] isEqualToString:@"getUserAgent"]) {
+    [self onGetUserAgent:call result:result];
   } else {
     result(FlutterMethodNotImplemented);
   }
@@ -228,6 +230,22 @@ - (void)clearCache:(FlutterResult)result {
   }
 }
 
+- (void)onGetUserAgent:(FlutterMethodCall*)call result:(FlutterResult)result {
+  [_webView evaluateJavaScript:@"navigator.userAgent"
+             completionHandler:^(NSString* userAgent, NSError* error) {
+               if (error) {
+                 result([FlutterError
+                     errorWithCode:@"userAgent_failed"
+                           message:@"Failed getting UserAgent"
+                           details:[NSString stringWithFormat:
+                                                 @"webview_flutter: fail evaluating JavaScript: %@",
+                                                 [error localizedDescription]]]);
+               } else {
+                 result(userAgent);
+               }
+             }];
+}
+
 - (void)applySettings:(NSDictionary<NSString*, id>*)settings {
   for (NSString* key in settings) {
     if ([key isEqualToString:@"jsMode"]) {
@@ -236,6 +254,9 @@ - (void)applySettings:(NSDictionary<NSString*, id>*)settings {
     } else if ([key isEqualToString:@"hasNavigationDelegate"]) {
       NSNumber* hasDartNavigationDelegate = settings[key];
       _navigationDelegate.hasDartNavigationDelegate = [hasDartNavigationDelegate boolValue];
+    } else if ([key isEqualToString:@"userAgent"]) {
+      NSString* userAgent = settings[key];
+      [self updateUserAgent:[userAgent isEqual:[NSNull null]] ? nil : userAgent];
     } else {
       NSLog(@"webview_flutter: unknown setting key: %@", key);
     }
@@ -274,6 +295,14 @@ - (bool)loadRequest:(NSDictionary<NSString*, id>*)request {
   return false;
 }
 
+- (void)updateUserAgent:(NSString*)userAgent {
+  if (@available(iOS 9.0, *)) {
+    [_webView setCustomUserAgent:userAgent];
+  } else {
+    NSLog(@"Updating UserAgent is not supported for Flutter WebViews prior to iOS 9.");
+  }
+}
+
 - (bool)loadUrl:(NSString*)url {
   return [self loadUrl:url withHeaders:[NSMutableDictionary dictionary]];
 }

packages/webview_flutter/lib/webview_flutter.dart

@@ -119,6 +119,7 @@ class WebView extends StatefulWidget {
     this.javascriptMode = JavascriptMode.disabled,
     this.javascriptChannels,
     this.navigationDelegate,
+    this.userAgent,
     this.gestureRecognizers,
     this.onPageFinished,
     this.debuggingEnabled = false,
@@ -256,6 +257,9 @@ class WebView extends StatefulWidget {
   /// By default `debuggingEnabled` is false.
   final bool debuggingEnabled;
 
+  /// The custom UserAgent.
+  final String userAgent;
+
   @override
   State<StatefulWidget> createState() => _WebViewState();
 }
@@ -349,25 +353,29 @@ class _WebSettings {
     this.javascriptMode,
     this.hasNavigationDelegate,
     this.debuggingEnabled,
+    this.userAgent,
   });
 
   static _WebSettings fromWidget(WebView widget) {
     return _WebSettings(
       javascriptMode: widget.javascriptMode,
       hasNavigationDelegate: widget.navigationDelegate != null,
       debuggingEnabled: widget.debuggingEnabled,
+      userAgent: widget.userAgent,
     );
   }
 
   final JavascriptMode javascriptMode;
   final bool hasNavigationDelegate;
   final bool debuggingEnabled;
+  final String userAgent;
 
   Map<String, dynamic> toMap() {
     return <String, dynamic>{
       'jsMode': javascriptMode.index,
       'hasNavigationDelegate': hasNavigationDelegate,
       'debuggingEnabled': debuggingEnabled,
+      'userAgent': userAgent,
     };
   }
 
@@ -384,6 +392,9 @@ class _WebSettings {
       updates['debuggingEnabled'] = newSettings.debuggingEnabled;
     }
 
+    if (userAgent != newSettings.userAgent) {
+      updates['userAgent'] = newSettings.userAgent;
+    }
     return updates;
   }
 }
@@ -529,6 +540,11 @@ class WebViewController {
     return _channel.invokeMethod("reload");
   }
 
+  /// Returns the User-Agent value that will be used for subsequent HTTP requests.
+  Future<String> getUserAgent() async {
+    return await _channel.invokeMethod('getUserAgent');
+  }
+
   /// Clears all caches used by the [WebView].
   ///
   /// The following caches are cleared:

packages/webview_flutter/test/webview_flutter_test.dart

@@ -70,6 +70,42 @@ void main() {
     expect(platformWebView.javascriptMode, JavascriptMode.disabled);
   });
 
+  testWidgets('Set UserAgent', (WidgetTester tester) async {
+    await tester.pumpWidget(const WebView(
+      initialUrl: 'https://youtube.com',
+      javascriptMode: JavascriptMode.unrestricted,
+    ));
+
+    final FakePlatformWebView platformWebView =
+        fakePlatformViewsController.lastCreatedView;
+
+    expect(platformWebView.userAgent, isNull);
+
+    await tester.pumpWidget(const WebView(
+      initialUrl: 'https://youtube.com',
+      javascriptMode: JavascriptMode.unrestricted,
+      userAgent: 'UA',
+    ));
+
+    expect(platformWebView.userAgent, 'UA');
+  });
+
+  testWidgets('Get UserAgent', (WidgetTester tester) async {
+    WebViewController controller;
+    await tester.pumpWidget(
+      WebView(
+        initialUrl: 'https://youtube.com',
+        javascriptMode: JavascriptMode.unrestricted,
+        userAgent: 'UA',
+        onWebViewCreated: (WebViewController webViewController) {
+          controller = webViewController;
+        },
+      ),
+    );
+    expect(controller, isNotNull);
+    expect(await controller.getUserAgent(), 'UA');
+  });
+
   testWidgets('Load url', (WidgetTester tester) async {
     WebViewController controller;
     await tester.pumpWidget(
@@ -823,6 +859,7 @@ class FakePlatformWebView {
     hasNavigationDelegate =
         params['settings']['hasNavigationDelegate'] ?? false;
     debuggingEnabled = params['settings']['debuggingEnabled'];
+    userAgent = params['settings']['userAgent'];
 
     channel = MethodChannel(
         'plugins.flutter.io/webview_$id', const StandardMethodCodec());
@@ -842,13 +879,16 @@ class FakePlatformWebView {
 
   bool hasNavigationDelegate;
   bool debuggingEnabled;
+  String userAgent;
 
   Future<dynamic> onMethodCall(MethodCall call) {
     switch (call.method) {
       case 'loadUrl':
         final Map<dynamic, dynamic> request = call.arguments;
         _loadUrl(request['url']);
         return Future<void>.sync(() {});
+      case 'userAgent':
+        return Future<String>.value(userAgent);
       case 'updateSettings':
         if (call.arguments['jsMode'] != null) {
           javascriptMode = JavascriptMode.values[call.arguments['jsMode']];
@@ -859,6 +899,9 @@ class FakePlatformWebView {
         if (call.arguments['debuggingEnabled'] != null) {
           debuggingEnabled = call.arguments['debuggingEnabled'];
         }
+        if (call.arguments['userAgent'] != null) {
+          userAgent = call.arguments['userAgent'];
+        }
         break;
       case 'canGoBack':
         return Future<bool>.sync(() => currentPosition > 0);