Ha, ha, so after 24 hours of scrambling, I find changing the class variable from system… to application music player solves the issue, and my app is back up and running. But the writing is still on the wall…
tcollette1
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I came across this post while searching for a solution to my Mac Catalyst music app not functioning upon upgrading to Sonoma. It seems the MPMusicPlayerController class no longer responds to calls within a SystemMusicPlayer setting, leaving labels displaying song title, artist, etc. blank, and of course, no ability to set queues! It would appear Apple is intent on herding everyone into its pay-to-play MusicKit and leaving tinkerers like me out to dry. Way to go😒
I resigned myself to this a while back, and have employed a similar workaround as you describe here. Thanks for the acknowledgment, though!
This is close enough to my solution, just using the playback state instead of a boolean variable. I discovered that when I upgraded to Monterey this month my MPMusicPlayerControllerNowPlayingItemDidChange notification began giving me the same treatment: work once and done, leading to yet another code around. I posted about it here around the time I came across this post. If you have the same problem, please drop a comment about any ideas you might have as well!