[Bug]: Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#initialize on channel OneSignal)

[GeylanKalafMohe]

What happened?

App does not start properly (MissingPluginException(No implementation found for method OneSignal#initialize on channel OneSignal)
because of OneSignal package issue which is ONLY happening on Android Release Build, on android debug build it is working fine. On iOS it is working fine also.

Logs:

✓ Built build/app/outputs/flutter-apk/app-release.apk (43.4MB)
I/flutter (15134): [IMPORTANT:flutter/shell/platform/android/android_context_gl_impeller.cc(94)] Using the Impeller rendering backend (OpenGLES).
E/flutter (15134): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#initialize on channel OneSignal)
E/flutter (15134): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:368)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): 
E/flutter (15134): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#lifecycleInit on channel OneSignal#inappmessages)
E/flutter (15134): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:368)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): #1      OneSignalInAppMessages.lifecycleInit (package:onesignal_flutter/src/inappmessages.dart:77)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): 
E/flutter (15134): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#lifecycleInit on channel OneSignal#user)
E/flutter (15134): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:368)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): #1      OneSignalUser.lifecycleInit (package:onesignal_flutter/src/user.dart:197)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): 
E/flutter (15134): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#pushSubscriptionToken on channel OneSignal#pushsubscription)
E/flutter (15134): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:368)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): #1      OneSignalPushSubscription.lifecycleInit (package:onesignal_flutter/src/pushsubscription.dart:66)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): 
E/flutter (15134): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#permission on channel OneSignal#notifications)
E/flutter (15134): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:368)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): #1      OneSignalNotifications.lifecycleInit (package:onesignal_flutter/src/notifications.dart:118)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): 
E/flutter (15134): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#requestPermission on channel OneSignal#notifications)
E/flutter (15134): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:368)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): #1      OneSignalNotifications.requestPermission (package:onesignal_flutter/src/notifications.dart:88)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): #2      main.<anonymous closure> (package:iu_app/main.dart:87)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): 
E/flutter (15134): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: MissingPluginException(No implementation found for method OneSignal#addNativeClickListener on channel OneSignal#notifications)
E/flutter (15134): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:368)
E/flutter (15134): <asynchronous suspension>
E/flutter (15134): 

Steps to reproduce?

1. Update OneSignal to version 5.3.4
2. Use Flutter Version 3.29.2
3. Try to initialize OneSignal in main.dart
4. Run the project in Android Production

---- Code ----

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  if (Constants.isCrashlyticsEnabled) {
    await Firebase.initializeApp(
        options: DefaultFirebaseOptions.currentPlatform);
    FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterError;
  }

  OneSignal.initialize(Constants.onesignalAppID);

  // some code that calls OneSignal.User.setLanguage()
  // .... some other code

  if (kDebugMode) {
    OneSignal.Debug.setLogLevel(OSLogLevel.verbose);
  }

  // The promptForPushNotificationsWithUserResponse function will show the iOS or Android push notification prompt. We recommend removing the following code and instead using an In-App Message to prompt for notification permission
  OneSignal.Notifications.requestPermission(false).then((accepted) {
    Helper.talker.debug("Accepted permission: $accepted");
  });

  OneSignal.Notifications.addClickListener((openedResult) {
    openedFromNotfication = true;
  });

  runApp(
    ChangeNotifierProvider<SettingsProvider>(
      create: (context) => settingsProvider,
      child: const MyApp(),
    ),
  );
}

What did you expect to happen?

OneSignal should be initialized and working fine like in debug mode.

OneSignal Flutter SDK version

Release 3.29.2

Which platform(s) are affected?

• iOS
• Android

Relevant log output

$ flutter doctor -v
[✓] Flutter (Channel stable, 3.29.2, on macOS 15.3.2 24D81 darwin-arm64, locale en-SA) [5.5s]
    • Flutter version 3.29.2 on channel stable at /Users/myuser/fvm/versions/3.29.2
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision c236373904 (8 months ago), 2025-03-13 16:17:06 -0400
    • Engine revision 18b71d647a
    • Dart version 3.7.2
    • DevTools version 2.42.3

[✓] Android toolchain - develop for Android devices (Android SDK version 35.0.0) [10.0s]
    • Android SDK at /Users/myuser/Library/Android/sdk
    • Platform android-35, build-tools 35.0.0
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
      This is the JDK bundled with the latest Android Studio installation on this machine.
      To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
    • Java version OpenJDK Runtime Environment (build 21.0.5+-12932927-b750.29)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 16.3) [9.8s]
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 16E140
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web [45ms]
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2024.3) [41ms]
    • 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 21.0.5+-12932927-b750.29)

[✓] Connected device (4 available) [10.8s]
    • FRL L22 (mobile)                • 8QCNW22629000690      • android-arm64  • Android 10 (API 29)
    • macOS (desktop)                 • macos                 • darwin-arm64   • macOS 15.3.2 24D81 darwin-arm64
    • Mac Designed for iPad (desktop) • mac-designed-for-ipad • darwin         • macOS 15.3.2 24D81 darwin-arm64
    • Chrome (web)                    • chrome                • web-javascript • Google Chrome 142.0.7444.60
    ! Error: Browsing on the local area network for iPhone 15 Pro G. Ensure the device is unlocked and attached with a
      cable or associated with the same local area network as this Mac.
      The device must be opted into Developer Mode to connect wirelessly. (code -27)
    ! Error: Browsing on the local area network for iPhone (650). Ensure the device is unlocked and attached with a cable
      or associated with the same local area network as this Mac.
      The device must be opted into Developer Mode to connect wirelessly. (code -27)
    ! Error: Browsing on the local area network for iPhone. Ensure the device is unlocked and attached with a cable or
      associated with the same local area network as this Mac.
      The device must be opted into Developer Mode to connect wirelessly. (code -27)

[✓] Network resources [991ms]
    • All expected network resources are available.

• No issues found!

Code of Conduct

• I agree to follow this project's Code of Conduct

[GeylanKalafMohe]

Proguard were stripping the OneSignal files for what ever reason. I guess the issue were introduced from upgrading AGP:

• Android Gradle Plugin 8.x changes:
  AGP 8.0+ made R8 more aggressive by default
  R8 runs more aggressively in release even without minifyEnabled true
  R8 optimization is stricter about unused code removal

So the solution was to add this to app/build.gradle :

   buildTypes {
       debug {
          signingConfig signingConfigs.debug
       }
       
       release {
           signingConfig signingConfigs.release
           // ProGuard rules to prevent OneSignal from being stripped
           // R8 runs even without minifyEnabled, so these rules help preserve classes
           // Use minimal/no optimization (minimize R8 impact)
           minifyEnabled false
           shrinkResources false
           // Use the most permissive ProGuard rules (or none)
           proguardFiles getDefaultProguardFile('proguard-android.txt')
       }
   }

[GeylanKalafMohe]

OneSignal should add this to their documentation