Visibility detector workaround for android impression issue (#610)

* Fix for #580. On android, wait for flutter widget to come into view before creating the PlatformViewLink

packages/google_mobile_ads/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 2.0.1
+* Bug fix for [issue 580](https://github.com/googleads/googleads-mobile-flutter/issues/580).
+  Adds a workaround on Android to wait for the ad widget to become visible
+  before attaching the platform view.
+
 ## 2.0.0
 * Updates GMA Android dependency to 21.0.0 and iOS to 9.6.0
 * Removes `credentials` from `AdapterResponseInfo`, which is replaced with

packages/google_mobile_ads/android/src/main/java/io/flutter/plugins/googlemobileads/Constants.java

@@ -17,7 +17,7 @@
 /** Constants used in the plugin. */
 public class Constants {
   /** Version request agent. Should be bumped alongside plugin versions. */
-  public static final String REQUEST_AGENT_PREFIX_VERSIONED = "Flutter-GMA-2.0.0";
+  public static final String REQUEST_AGENT_PREFIX_VERSIONED = "Flutter-GMA-2.0.1";
 
   static final String ERROR_CODE_UNEXPECTED_AD_TYPE = "unexpected_ad_type";
 }

packages/google_mobile_ads/ios/Classes/FLTConstants.h

@@ -13,4 +13,4 @@
 // limitations under the License.
 
 /** Versioned request agent string. */
-#define FLT_REQUEST_AGENT_VERSIONED @"Flutter-GMA-2.0.0"
+#define FLT_REQUEST_AGENT_VERSIONED @"Flutter-GMA-2.0.1"

packages/google_mobile_ads/lib/src/ad_containers.dart

@@ -20,6 +20,7 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
+import 'package:visibility_detector/visibility_detector.dart';
 
 import 'ad_instance_manager.dart';
 import 'ad_listeners.dart';
@@ -590,6 +591,7 @@ class AdWidget extends StatefulWidget {
 class _AdWidgetState extends State<AdWidget> {
   bool _adIdAlreadyMounted = false;
   bool _adLoadNotCalled = false;
+  bool _firstVisibleOccurred = false;
 
   @override
   void initState() {
@@ -635,28 +637,51 @@ class _AdWidgetState extends State<AdWidget> {
       ]);
     }
     if (defaultTargetPlatform == TargetPlatform.android) {
-      return PlatformViewLink(
-        viewType: '${instanceManager.channel.name}/ad_widget',
-        surfaceFactory:
-            (BuildContext context, PlatformViewController controller) {
-          return AndroidViewSurface(
-            controller: controller as AndroidViewController,
-            gestureRecognizers: const <Factory<OneSequenceGestureRecognizer>>{},
-            hitTestBehavior: PlatformViewHitTestBehavior.opaque,
-          );
-        },
-        onCreatePlatformView: (PlatformViewCreationParams params) {
-          return PlatformViewsService.initSurfaceAndroidView(
-            id: params.id,
-            viewType: '${instanceManager.channel.name}/ad_widget',
-            layoutDirection: TextDirection.ltr,
-            creationParams: instanceManager.adIdFor(widget.ad),
-            creationParamsCodec: StandardMessageCodec(),
-          )
-            ..addOnPlatformViewCreatedListener(params.onPlatformViewCreated)
-            ..create();
-        },
-      );
+      // Do not attach the platform view widget until it will actually become
+      // visible. This is a workaround for
+      // https://github.com/googleads/googleads-mobile-flutter/issues/580,
+      // where impressions are erroneously fired due to how platform views are
+      // rendered.
+      // TODO (jjliu15): Remove this after the flutter issue is resolved.
+      if (_firstVisibleOccurred) {
+        return PlatformViewLink(
+          viewType: '${instanceManager.channel.name}/ad_widget',
+          surfaceFactory:
+              (BuildContext context, PlatformViewController controller) {
+            return AndroidViewSurface(
+              controller: controller as AndroidViewController,
+              gestureRecognizers: const <
+                  Factory<OneSequenceGestureRecognizer>>{},
+              hitTestBehavior: PlatformViewHitTestBehavior.opaque,
+            );
+          },
+          onCreatePlatformView: (PlatformViewCreationParams params) {
+            return PlatformViewsService.initSurfaceAndroidView(
+              id: params.id,
+              viewType: '${instanceManager.channel.name}/ad_widget',
+              layoutDirection: TextDirection.ltr,
+              creationParams: instanceManager.adIdFor(widget.ad),
+              creationParamsCodec: StandardMessageCodec(),
+            )
+              ..addOnPlatformViewCreatedListener(params.onPlatformViewCreated)
+              ..create();
+          },
+        );
+      } else {
+        final adId = instanceManager.adIdFor(widget.ad);
+        return VisibilityDetector(
+          key: Key('android-platform-view-$adId'),
+          onVisibilityChanged: (visibilityInfo) {
+            if (!_firstVisibleOccurred &&
+                visibilityInfo.visibleFraction > 0.01) {
+              setState(() {
+                _firstVisibleOccurred = true;
+              });
+            }
+          },
+          child: Container(),
+        );
+      }
     }
 
     return UiKitView(

packages/google_mobile_ads/pubspec.yaml

@@ -31,6 +31,7 @@ dependencies:
   meta: ^1.0.4
   flutter:
     sdk: flutter
+  visibility_detector: ^0.3.3
 
 dev_dependencies:
   pedantic: ^1.11.0

packages/google_mobile_ads/test/ad_containers_test.dart

@@ -18,9 +18,9 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:google_mobile_ads/src/ad_instance_manager.dart';
 import 'package:google_mobile_ads/google_mobile_ads.dart';
-import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/services.dart';
+import 'package:visibility_detector/visibility_detector.dart';
 
 // ignore_for_file: deprecated_member_use_from_same_package
 void main() {
@@ -282,7 +282,8 @@ void main() {
       expect(instanceManager.adFor(0), isNotNull);
     });
 
-    testWidgets('build ad widget', (WidgetTester tester) async {
+    testWidgets('build ad widget iOS', (WidgetTester tester) async {
+      debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
       final NativeAd native = NativeAd(
         adUnitId: 'test-ad-unit',
         factoryId: '0',
@@ -293,41 +294,89 @@ void main() {
       await native.load();
 
       await tester.pumpWidget(
-        Builder(
-          builder: (BuildContext context) {
-            AdWidget widget = AdWidget(ad: native);
-            Widget buildWidget = widget.createElement().build();
-            expect(buildWidget, isA<PlatformViewLink>());
-            return widget;
-          },
+        MaterialApp(
+          home: Material(
+            child: SingleChildScrollView(
+              child: Column(
+                key: UniqueKey(),
+                children: [
+                  SizedBox.fromSize(size: Size(200, 1000)),
+                  Container(
+                    height: 200,
+                    width: 200,
+                    child: AdWidget(ad: native),
+                  ),
+                ],
+              ),
+            ),
+          ),
         ),
       );
+      await tester.pumpAndSettle();
+
+      final uiKitView = tester.widget(find.byType(UiKitView));
+      expect(uiKitView, isNotNull);
 
       await native.dispose();
+      debugDefaultTargetPlatformOverride = null;
     });
 
-    testWidgets('build ad widget', (WidgetTester tester) async {
-      final NativeAd native = NativeAd(
+    testWidgets('Build ad widget Android', (WidgetTester tester) async {
+      debugDefaultTargetPlatformOverride = TargetPlatform.android;
+      // Create a loaded ad
+      final ad = NativeAd(
         adUnitId: 'test-ad-unit',
         factoryId: '0',
         listener: NativeAdListener(),
         request: AdRequest(),
       );
+      await ad.load();
 
-      await native.load();
-
+      // Render ad in a scrolling view
+      VisibilityDetectorController.instance.updateInterval = Duration.zero;
       await tester.pumpWidget(
-        Builder(
-          builder: (BuildContext context) {
-            AdWidget widget = AdWidget(ad: native);
-            Widget buildWidget = widget.createElement().build();
-            expect(buildWidget, isA<PlatformViewLink>());
-            return widget;
-          },
+        MaterialApp(
+          home: Material(
+            child: SingleChildScrollView(
+              child: Column(
+                key: UniqueKey(),
+                children: [
+                  SizedBox.fromSize(size: Size(200, 1000)),
+                  Container(
+                    height: 200,
+                    width: 200,
+                    child: AdWidget(ad: ad),
+                  ),
+                ],
+              ),
+            ),
+          ),
         ),
       );
-
-      await native.dispose();
+      await tester.pumpAndSettle();
+
+      // On initial render, VisibilityRender should be in the UI
+      final visibilityDetectorWidget =
+          tester.widget(find.byKey(Key('android-platform-view-0')));
+      expect(visibilityDetectorWidget, isNotNull);
+      expect(visibilityDetectorWidget, isA<VisibilityDetector>());
+      final platformViewLinks =
+          tester.widgetList(find.byType(PlatformViewLink));
+      expect(platformViewLinks.isEmpty, true);
+
+      // Drag the ad widget into view
+      await tester.drag(find.byType(SingleChildScrollView), Offset(0.0, -1000));
+      await tester.pumpAndSettle();
+
+      // PlatformViewLink should now be present instead of VisibilityDetector
+      final detectors = tester.widgetList(find.byType(VisibilityDetector));
+      expect(detectors.isEmpty, true);
+      final platformViewLink = tester.widget(find.byType(PlatformViewLink));
+      expect(platformViewLink, isNotNull);
+
+      // Reset platform override
+      await ad.dispose();
+      debugDefaultTargetPlatformOverride = null;
     });
 
     testWidgets('warns when ad has not been loaded',