Unable to answer call in background service for android ?

[harryandroiddev]

Describe the bug
Unable to accept the incoming call in background service in android os .

To Reproduce
Steps to reproduce the behavior:

1. Start background service
2. register sip user and close the app
3. handle sip listeners and on incoming call accept the call .

The method to answer the call throws error
mediaStream = await navigator.mediaDevices.getUserMedia(
mediaConstraints,
); // getting error at this line of code
call?.answer(
helper!.buildCallOptions(true),
mediaStream: mediaStream,
);

Error Logs

E/MethodChannel#FlutterWebRTC.Method(23398): Failed to handle method call
E/MethodChannel#FlutterWebRTC.Method(23398): java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Intent android.app.Activity.registerReceiver(android.content.BroadcastReceiver, android.content.IntentFilter)' on a null object reference
E/MethodChannel#FlutterWebRTC.Method(23398): at com.cloudwebrtc.webrtc.video.camera.DeviceOrientationManager.start(DeviceOrientationManager.java:57)
E/MethodChannel#FlutterWebRTC.Method(23398): at com.cloudwebrtc.webrtc.video.camera.CameraUtils.(CameraUtils.java:48)
E/MethodChannel#FlutterWebRTC.Method(23398): at com.cloudwebrtc.webrtc.MethodCallHandlerImpl.initialize(MethodCallHandlerImpl.java:176)
E/MethodChannel#FlutterWebRTC.Method(23398): at com.cloudwebrtc.webrtc.MethodCallHandlerImpl.onMethodCall(MethodCallHandlerImpl.java:345)
E/MethodChannel#FlutterWebRTC.Method(23398): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:267)
E/MethodChannel#FlutterWebRTC.Method(23398): at io.flutter.embedding.engine.dart.DartMessenger.invokeHandler(DartMessenger.java:292)
E/MethodChannel#FlutterWebRTC.Method(23398): at io.flutter.embedding.engine.dart.DartMessenger.lambda$dispatchMessageToQueue$0$io-flutter-embedding-engine-dart-DartMessenger(DartMessenger.java:319)
E/MethodChannel#FlutterWebRTC.Method(23398): at io.flutter.embedding.engine.dart.DartMessenger$$ExternalSyntheticLambda0.run(D8$$SyntheticClass:0)
E/MethodChannel#FlutterWebRTC.Method(23398): at android.os.Handler.handleCallback(Handler.java:958)
E/MethodChannel#FlutterWebRTC.Method(23398): at android.os.Handler.dispatchMessage(Handler.java:99)
E/MethodChannel#FlutterWebRTC.Method(23398): at android.os.Looper.loopOnce(Looper.java:230)
E/MethodChannel#FlutterWebRTC.Method(23398): at android.os.Looper.loop(Looper.java:319)
E/MethodChannel#FlutterWebRTC.Method(23398): at android.app.ActivityThread.main(ActivityThread.java:8893)
E/MethodChannel#FlutterWebRTC.Method(23398): at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#FlutterWebRTC.Method(23398): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:608)
E/MethodChannel#FlutterWebRTC.Method(23398): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1103)
E/flutter (23398): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: Unable to getUserMedia: Attempt to invoke virtual method 'android.content.Intent android.app.Activity.registerReceiver(android.content.BroadcastReceiver, android.content.IntentFilter)' on a null object reference
E/flutter (23398): #0 MediaDeviceNative.getUserMedia (package:flutter_webrtc/src/native/mediadevices_impl.dart:48:7)

Expected behavior
Answer the call in background

System Infomation()
[✓] Flutter (Channel stable, 3.29.2, on macOS 15.3.1 24D70 darwin-arm64, locale en-IN)
[✓] Android toolchain - develop for Android devices (Android SDK version 35.0.0-rc4)
[✓] Xcode - develop for iOS and macOS (Xcode 16.2)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2024.3)
[✓] VS Code (version 1.98.2)
[✓] Connected device (5 available)
[✓] Network resources

[VictorUvarov]

I believe the issue is because you need to call on the main thread. The SIP logic can be on the background thread, the UI and webrtc logic needs to be on the main thread. Currently both are tightly coupled in this plugin.

navigator.mediaDevices.getUserMedia(mediaConstraints)