c# - Wrong Thread Exception when changing an object's property from an event delegate -


i have playbackmodel class instantiate in mainpage of app, so:

if(playbackmodel.current == null) new playbackmodel();

i use playbackmodel storing references objects use in app. works viewmodel majority of pages. defines these properties, among others:

public mediaplayer player { get; set; } public mediaplaybackstate playbackstate { get; set; } public repeatmode repeatmode { get; set; } public mediaplaybacklist queue { get; set; } [alsonotifyfor("currentindex", "currenttrack")] public mediaplaybackitem currentitem { get; set; } public observablecollection<playbackitemviewmodel> tracks { get; set; } public int currentindex {     {         return (int)queue.currentitemindex;     } set {         system.diagnostics.debug.writeline("currentindex setter called! value: "+value);         if (value >= 0 && queue.items.count() > value && value != queue.currentitemindex)             queue.moveto((uint)value);     } } public playbackitemviewmodel currenttrack { { if (currentindex == -1) return null; if (tracks.count() > currentindex) return tracks[currentindex]; else return null; } } private timespan _currentposition; public timespan currentposition { { return _currentposition; } set { _currentposition = value; player.playbacksession.position = _currentposition; } } public timespan currentduration { get; set; } public library library { get; set; } public lastfmclient lastfm { get; set; }

in inspector of playbackmodel i'm subscribing events keep track of what's going on media player , queue, can later display in ui. example:

player.playbacksession.playbackstatechanged += (o, ea) => {         playbackstate = o.playbackstate; };

but won't work. throws wrong_thread exception. it's same these other events. tried using await coreapplication.mainview.corewindow.dispatcher.runasync() method run code on ui thread understand it, won't work when app in background playback mode. how can other way works supports background playback?

for decided use itemchanged event:

queue.currentitemchanged += async (o, ea) => {     await coreapplication.mainview.corewindow.dispatcher.runasync(coredispatcherpriority.normal, () =>     {         var pos = currentposition.duration();         var bg = app.ref.isbackground;         task<scrobbleresponse> res = null;         currentposition = timespan.zero;         currentitem = o.currentitem;         if (ea.olditem != null)         {             var vm = ea.olditem.source.customproperties["vm"] playbackitemviewmodel;             if (pos.totalseconds >= ea.olditem.source.duration.value.totalseconds * 0.9)             {                 res = lastfm.scrobbler.scrobbleasync(new scrobble(vm.artist, vm.album, vm.title, datetimeoffset.now));             }         }         if (currentitem != null)             currentduration = o.currentitem.source.duration.value;         else currentduration = timespan.zero;     }); };

is there other way it?

thanks!

the code in dispatcher runs correctly. it's if statement that's not being called due conditions not updating in background. bad.


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