Reacting to media play button doesn't work when Sweyer is not running

[Abestanis]

Steps to reproduce

1. Make sure Sweyer is not running (force close the app).
2. Trigger a KEYCODE_MEDIA_PLAY event or KEYCODE_MEDIA_PLAY_PAUSE event, e.g. press the play button on a connected headset.
3. Observe the logcat logs.

What did you expect?

The app should be able to start from the audio_service and start playing audio.

What happened instead?

The app does start in the background, but never plays audio. This is because the following error is thrown:

Error

I/System.out: ### onAttachedToEngine
I/System.out: ### 1 client handlers
I/System.out: ### new AudioHandlerInterface
I/System.out: ### connect
D/MediaBrowserCompat: Connecting to a MediaBrowserService.
I/System.out: ### connect returned
I/System.out: ### onAttachedToEngine completed
D/DeviceInfoPlugin: Use TaskQueues.
I/System.out: flutterEngine warmed up
I/System.out: ### onStartCommand
I/System.out: ### onMediaButtonEvent: KeyEvent { action=ACTION_DOWN, keyCode=KEYCODE_MEDIA_PLAY_PAUSE, scanCode=0, metaState=0, flags=0x0, repeatCount=0, eventTime=0, downTime=0, deviceId=-1, source=0x0, displayId=0 }
2022-06-26 17:39:10.733 6154-6154/com.nt4f04und.sweyer I/System.out: ### listener = com.ryanheise.audioservice.AudioServicePlugin$AudioHandlerInterface@8194acc
I/System.out: ### calling onClick
I/System.out: ### sending click map: {button=0}
I/System.out: ### called onClick
I/System.out: ### onGetRoot. isRecentRequest=false
I/System.out: ### onConnected
I/System.out: ### registered mediaController callback
I/System.out: ### onConnected returned
I/flutter: The Dart VM service is listening on http://127.0.0.1:45025/VEcJ_HFwVvI=/
I/flutter: ----------------FIREBASE CRASHLYTICS----------------
I/flutter: MissingPluginException(No implementation found for method retrieveSongs on channel content_channel)
I/flutter: #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:165:7)
    <asynchronous suspension>
    #1      MethodChannel.invokeListMethod (package:flutter/src/services/platform_channel.dart:353:35)
    <asynchronous suspension>
    #2      ContentChannel.retrieveSongs (package:sweyer/logic/player/content_channel.dart:113:18)
    <asynchronous suspension>
    #3      ContentControl.refetch.<anonymous closure> (package:sweyer/logic/player/content.dart:444:33)
    <asynchronous suspension>
    #4      ContentControl.refetch (package:sweyer/logic/player/content.dart:441:5)
    <asynchronous suspension>
    #5      Future.wait.<anonymous closure> (dart:async/future.dart:521:21)
    <asynchronous suspension>
    #6      Future.any.onValue (dart:async/future.dart:611:5)
    <asynchronous suspension>

The reason for the error is that ContentChannel initialization is triggered by MainActivity.onCreate, but when the app is not running and we are starting via the audio service, no MainActivity is ever created and therefore the MethodChannel is never registered.

The only workaround I found (suggested by https://github.com/ryanheise/audio_service/issues/399#issuecomment-657326724) is to extract the method channel into a separate plugin and use the plugin registration system to initialize the method channel under all conditions.

@nt4f04uNd do you have a better idea how to approach this?

Sweyer version

Latest on the 1.0.8 branch; c6386e62fcae56165233ab1c09e0d7f024075cc2

Android version

No response

[Abestanis]

I can confirm that extracting the content channel and pretty much all of our Java code into a plugin solves the issue.