NPE caused by native ads after switching between pages and sending the app to background

Plugin Version

google_mobile_ads 1.0.1

Steps to Reproduce

1. Implement native ads following the Kotlin example from codelabs
2. Open app, check that the native ad is loaded and visible
3. Open a drawer in the app or open a different page in the app so the native ad is covered
4. Send the app to background

Expected results: App doesn’t crash

Actual results: App crashes

Logs

E/AndroidRuntime(30623): FATAL EXCEPTION: main
E/AndroidRuntime(30623): Process: com.my.app, PID: 30623
E/AndroidRuntime(30623): java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.dispatchWindowVisibilityChanged(int)' on a null object reference
E/AndroidRuntime(30623): 	at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1290)
E/AndroidRuntime(30623): 	at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1290)
E/AndroidRuntime(30623): 	at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1290)
E/AndroidRuntime(30623): 	at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1290)
E/AndroidRuntime(30623): 	at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1290)
E/AndroidRuntime(30623): 	at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1813)
E/AndroidRuntime(30623): 	at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1515)
E/AndroidRuntime(30623): 	at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7091)
E/AndroidRuntime(30623): 	at android.view.Choreographer$CallbackRecord.run(Choreographer.java:927)
E/AndroidRuntime(30623): 	at android.view.Choreographer.doCallbacks(Choreographer.java:702)
E/AndroidRuntime(30623): 	at android.view.Choreographer.doFrame(Choreographer.java:638)
E/AndroidRuntime(30623): 	at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:913)
E/AndroidRuntime(30623): 	at android.os.Handler.handleCallback(Handler.java:751)
E/AndroidRuntime(30623): 	at android.os.Handler.dispatchMessage(Handler.java:95)
E/AndroidRuntime(30623): 	at android.os.Looper.loop(Looper.java:154)
E/AndroidRuntime(30623): 	at android.app.ActivityThread.main(ActivityThread.java:6682)
E/AndroidRuntime(30623): 	at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime(30623): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
E/AndroidRuntime(30623): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

flutter doctor -v
[✓] Flutter (Channel stable, 2.8.1, on macOS 11.3.1 20E241 darwin-x64, locale en-US)
    • Flutter version 2.8.1 at /Users/me/Downloads/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 77d935af4d (2 weeks ago), 2021-12-16 08:37:33 -0800
    • Engine revision 890a5fca2e
    • Dart version 2.15.1

[✓] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
    • Android SDK at /Users/me/Library/Android/sdk
    • Platform android-31, build-tools 31.0.0
    • ANDROID_HOME =
      /usr/local/opt/python@3.8/bin:/Users/me/.rvm/gems/ruby-2.7.0/bin:/Users/me/.rvm/gems/ruby-2.7.0@global/bin:/Users/me/.rvm/rubies/ruby-2.7.0/bin:/usr/local/bin:/usr/local
      /bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/Apple/usr/bin:/Users/me/n/bin:/Users/me/.rvm/bin:/Users/me/Library/Android/sdk/tools:/Users/me/Library/Android/sdk:/Use
      rs/me/Library/Android/sdk/platform-tools:/Users/me/Library/Android/sdk/tools
    • ANDROID_SDK_ROOT = /Users/me/Library/Android/sdk/
    • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 13.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • CocoaPods version 1.11.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2020.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)

[✓] IntelliJ IDEA Community Edition (version 2020.1.4)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin version 56.0.1
    • Dart plugin version 201.9380

[✓] VS Code (version 1.50.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.17.0

[✓] Connected device (3 available)
    • SM G920F (mobile) • 03157df394036a23    • android-arm64  • Android 7.0 (API 24)

• No issues found!

The crash occurs on Android, reproduced it on devices from Android 7 to Android 11 and there are several crashes in production as well. Tried with older version of Flutter, same crash. Also older versions of the plugin provoke the same issue.

Is the codelabs example missing some additional setup or is this plugin just unusable in the current state?

[kreativityapps]

Hi @maheshmnj , thank you for the quick reply.

After checking the code in detail I found what caused the problem in my case.

To try to improve native ad performance I called PlatformViewsService.synchronizeToNativeViewHierarchy(false) in Flutter main. After removing this it doesn’t crashes anymore.

Performance is still terrible because of the ad also in the example app, but that’s another topic. At least the crash is gone.

Thank you!

[maheshmnj]

Thanks for the info @kreativityapps, Glad you solved it.

Performance is still terrible because of the ad also in the example app, but that’s another topic. At least the crash is gone.

I agree there are performance issues and they are being tracked in the repo. Please follow up there for further updates.

Closing as solved.