[webview_flutter] Add async NavigationDelegates (flutter#2257)

Previously all navigation decisions needed to be made synchronously in Dart. The platform layers are already waiting for the MethodChannel callback, so just changed the return type to be `FutureOr<NavigationDecision>'. This is a change to the method signature of `WebViewPlatformCallbacksHandler#onNavigationRequest`, but that interface appears to only be meant to be implemented internally to the plugin.
ditman · ditman · Nov 13, 2019 · Nov 13, 2019 · Nov 14, 2019 · Nov 14, 2019
commit d22502af8f0f9fde5f8cefee95cea5a9bc9bd094
diff --git a/packages/webview_flutter/CHANGELOG.md b/packages/webview_flutter/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 0.3.16
+
+* Add support for async NavigationDelegates. Synchronous NavigationDelegates
+  should still continue to function without any change in behavior.
+
 ## 0.3.15+3
 
 * Re-land support for the v2 Android embedding. This correctly sets the minimum

diff --git a/packages/webview_flutter/example/test_driver/webview_flutter_e2e.dart b/packages/webview_flutter/example/test_driver/webview_flutter_e2e.dart
@@ -494,6 +494,123 @@ void main() {
     final String title = await controller.getTitle();
     expect(title, 'Some title');
   });
+
+  group('NavigationDelegate', () {
+    final String blankPage = "<!DOCTYPE html><head></head><body></body></html>";
+    final String blankPageEncoded = 'data:text/html;charset=utf-8;base64,' +
+        base64Encode(const Utf8Encoder().convert(blankPage));
+
+    testWidgets('can allow requests', (WidgetTester tester) async {
+      final Completer<WebViewController> controllerCompleter =
+          Completer<WebViewController>();
+      final StreamController<String> pageLoads =
+          StreamController<String>.broadcast();
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: WebView(
+            key: GlobalKey(),
+            initialUrl: blankPageEncoded,
+            onWebViewCreated: (WebViewController controller) {
+              controllerCompleter.complete(controller);
+            },
+            javascriptMode: JavascriptMode.unrestricted,
+            navigationDelegate: (NavigationRequest request) {
+              return (request.url.contains('youtube.com'))
+                  ? NavigationDecision.prevent
+                  : NavigationDecision.navigate;
+            },
+            onPageFinished: (String url) => pageLoads.add(url),
+          ),
+        ),
+      );
+
+      await pageLoads.stream.first; // Wait for initial page load.
+      final WebViewController controller = await controllerCompleter.future;
+      await controller
+          .evaluateJavascript('location.href = "https://www.google.com/"');
+
+      await pageLoads.stream.first; // Wait for the next page load.
+      final String currentUrl = await controller.currentUrl();
+      expect(currentUrl, 'https://www.google.com/');
+    });
+
+    testWidgets('can block requests', (WidgetTester tester) async {
+      final Completer<WebViewController> controllerCompleter =
+          Completer<WebViewController>();
+      final StreamController<String> pageLoads =
+          StreamController<String>.broadcast();
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: WebView(
+            key: GlobalKey(),
+            initialUrl: blankPageEncoded,
+            onWebViewCreated: (WebViewController controller) {
+              controllerCompleter.complete(controller);
+            },
+            javascriptMode: JavascriptMode.unrestricted,
+            navigationDelegate: (NavigationRequest request) {
+              return (request.url.contains('youtube.com'))
+                  ? NavigationDecision.prevent
+                  : NavigationDecision.navigate;
+            },
+            onPageFinished: (String url) => pageLoads.add(url),
+          ),
+        ),
+      );
+
+      await pageLoads.stream.first; // Wait for initial page load.
+      final WebViewController controller = await controllerCompleter.future;
+      await controller
+          .evaluateJavascript('location.href = "https://www.youtube.com/"');
+
+      // There should never be any second page load, since our new URL is
+      // blocked. Still wait for a potential page change for some time in order
+      // to give the test a chance to fail.
+      await pageLoads.stream.first
+          .timeout(const Duration(milliseconds: 500), onTimeout: () => null);
+      final String currentUrl = await controller.currentUrl();
+      expect(currentUrl, isNot(contains('youtube.com')));
+    });
+
+    testWidgets('supports asynchronous decisions', (WidgetTester tester) async {
+      final Completer<WebViewController> controllerCompleter =
+          Completer<WebViewController>();
+      final StreamController<String> pageLoads =
+          StreamController<String>.broadcast();
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: WebView(
+            key: GlobalKey(),
+            initialUrl: blankPageEncoded,
+            onWebViewCreated: (WebViewController controller) {
+              controllerCompleter.complete(controller);
+            },
+            javascriptMode: JavascriptMode.unrestricted,
+            navigationDelegate: (NavigationRequest request) async {
+              NavigationDecision decision = NavigationDecision.prevent;
+              decision = await Future<NavigationDecision>.delayed(
+                  const Duration(milliseconds: 10),
+                  () => NavigationDecision.navigate);
+              return decision;
+            },
+            onPageFinished: (String url) => pageLoads.add(url),
+          ),
+        ),
+      );
+
+      await pageLoads.stream.first; // Wait for initial page load.
+      final WebViewController controller = await controllerCompleter.future;
+      await controller
+          .evaluateJavascript('location.href = "https://www.google.com"');
+
+      await pageLoads.stream.first; // Wait for second page to load.
+      final String currentUrl = await controller.currentUrl();
+      expect(currentUrl, 'https://www.google.com/');
+    });
+  });
 }
 
 // JavaScript booleans evaluate to different string values on Android and iOS.

diff --git a/packages/webview_flutter/lib/platform_interface.dart b/packages/webview_flutter/lib/platform_interface.dart
@@ -21,7 +21,7 @@ abstract class WebViewPlatformCallbacksHandler {
   /// Invoked by [WebViewPlatformController] when a navigation request is pending.
   ///
   /// If true is returned the navigation is allowed, otherwise it is blocked.
-  bool onNavigationRequest({String url, bool isForMainFrame});
+  FutureOr<bool> onNavigationRequest({String url, bool isForMainFrame});
 
   /// Invoked by [WebViewPlatformController] when a page has finished loading.
   void onPageFinished(String url);

diff --git a/packages/webview_flutter/lib/src/webview_method_channel.dart b/packages/webview_flutter/lib/src/webview_method_channel.dart
@@ -31,7 +31,7 @@ class MethodChannelWebViewPlatform implements WebViewPlatformController {
         _platformCallbacksHandler.onJavaScriptChannelMessage(channel, message);
         return true;
       case 'navigationRequest':
-        return _platformCallbacksHandler.onNavigationRequest(
+        return await _platformCallbacksHandler.onNavigationRequest(
           url: call.arguments['url'],
           isForMainFrame: call.arguments['isForMainFrame'],
         );

diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
@@ -67,7 +67,8 @@ enum NavigationDecision {
 /// `navigation` should be handled.
 ///
 /// See also: [WebView.navigationDelegate].
-typedef NavigationDecision NavigationDelegate(NavigationRequest navigation);
+typedef FutureOr<NavigationDecision> NavigationDelegate(
+    NavigationRequest navigation);
 
 /// Signature for when a [WebView] has finished loading a page.
 typedef void PageFinishedCallback(String url);
@@ -439,11 +440,12 @@ class _PlatformCallbacksHandler implements WebViewPlatformCallbacksHandler {
   }
 
   @override
-  bool onNavigationRequest({String url, bool isForMainFrame}) {
+  FutureOr<bool> onNavigationRequest({String url, bool isForMainFrame}) async {
     final NavigationRequest request =
         NavigationRequest._(url: url, isForMainFrame: isForMainFrame);
     final bool allowNavigation = _widget.navigationDelegate == null ||
-        _widget.navigationDelegate(request) == NavigationDecision.navigate;
+        await _widget.navigationDelegate(request) ==
+            NavigationDecision.navigate;
     return allowNavigation;
   }
 

diff --git 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: 0.3.15+3
+version: 0.3.16
 author: Flutter Team <[email protected]>
 homepage: https://github.com/flutter/plugins/tree/master/packages/webview_flutter