/// <summary>
/// Handles background task cancellation. Task cancellation happens due to :
/// 1. Another Media app comes into foreground and starts playing music
/// 2. Resource pressure. Your task is consuming more CPU and memory than allowed.
/// In either case, save state so that if foreground app resumes it can know where to start.
/// </summary>
private void OnCanceled(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason)
{
// You get some time here to save your state before process and resources are reclaimed
Debug.WriteLine("MyBackgroundAudioTask " + sender.Task.TaskId + " Cancel Requested...");
try
{
//save state
ApplicationSettingsHelper.SaveSettingsValue(BackgroundAudioConstants.CurrentTrack, Playlist.CurrentTrackIndex);
ApplicationSettingsHelper.SaveSettingsValue(BackgroundAudioConstants.Position, BackgroundMediaPlayer.Current.Position.ToString());
ApplicationSettingsHelper.SaveSettingsValue(BackgroundAudioConstants.Time, BackgroundMediaPlayer.Current.NaturalDuration.ToString());
ApplicationSettingsHelper.SaveSettingsValue(BackgroundAudioConstants.BackgroundTaskState, BackgroundAudioConstants.BackgroundTaskCancelled);
ApplicationSettingsHelper.SaveSettingsValue(BackgroundAudioConstants.AppState, Enum.GetName(typeof(ForegroundAppStatus), foregroundAppState));
backgroundtaskrunning = false;
//unsubscribe event handlers
systemmediatransportcontrol.ButtonPressed -= systemmediatransportcontrol_ButtonPressed;
systemmediatransportcontrol.PropertyChanged -= systemmediatransportcontrol_PropertyChanged;
Playlist.TrackChanged -= playList_TrackChanged;
//clear objects task cancellation can happen uninterrupted
playlistManager.ResetCollection((int)ResetType.NormalReset);
playlistManager = null;
// Send message to foreground task (if it's around) that this task was cancelled :(
ValueSet message = new ValueSet {
{ BackgroundAudioConstants.BackgroundTaskCancelled, "" }
};
BackgroundMediaPlayer.SendMessageToForeground(message);
BackgroundMediaPlayer.Shutdown(); // shutdown media pipeline
}
catch (Exception ex)
{
Debug.WriteLine(ex.ToString());
}
deferral?.Complete(); // signals task completion.
Debug.WriteLine("MyBackgroundAudioTask Cancel complete...");
}
/// <summary>
/// The Run method is the entry point of a background task.
/// </summary>
/// <param name="taskInstance"></param>
public void Run(IBackgroundTaskInstance taskInstance)
{
try
{
Debug.WriteLine("Background Audio Task " + taskInstance.Task.Name + " starting...");
// Initialize SMTC object to talk with UVC.
//Note that, this is intended to run after app is paused and
//hence all the logic must be written to run in background process
systemmediatransportcontrol = SystemMediaTransportControls.GetForCurrentView();
systemmediatransportcontrol.ButtonPressed += systemmediatransportcontrol_ButtonPressed;
systemmediatransportcontrol.PropertyChanged += systemmediatransportcontrol_PropertyChanged;
systemmediatransportcontrol.IsEnabled = true;
systemmediatransportcontrol.IsPauseEnabled = true;
systemmediatransportcontrol.IsPlayEnabled = true;
systemmediatransportcontrol.IsNextEnabled = true;
systemmediatransportcontrol.IsPreviousEnabled = true;
// Associate a cancellation and completed handlers with the background task.
taskInstance.Canceled += new BackgroundTaskCanceledEventHandler(OnCanceled);
taskInstance.Task.Completed += Taskcompleted;
var value = ApplicationSettingsHelper.ReadResetSettingsValue(BackgroundAudioConstants.AppState);
if (value == null)
{
foregroundAppState = ForegroundAppStatus.Unknown;
}
else
{
foregroundAppState = (ForegroundAppStatus)Enum.Parse(typeof(ForegroundAppStatus), value.ToString());
}
//Add handlers for MediaPlayer
BackgroundMediaPlayer.Current.CurrentStateChanged += Current_CurrentStateChanged;
//Add handlers for playlist trackchanged
Playlist.TrackChanged += playList_TrackChanged;
//Initialize message channel
BackgroundMediaPlayer.MessageReceivedFromForeground += BackgroundMediaPlayer_MessageReceivedFromForeground;
//Send information to foreground that background task has been started if app is active
if (foregroundAppState != ForegroundAppStatus.Suspended)
{
ValueSet message = new ValueSet();
message.Add(BackgroundAudioConstants.BackgroundTaskStarted, "");
BackgroundMediaPlayer.SendMessageToForeground(message);
}
BackgroundTaskStarted.Set();
backgroundtaskrunning = true;
Playlist.PopulatePlaylist();
var currentTrackIndex = ApplicationSettingsHelper.ReadSettingsValue(BackgroundAudioConstants.CurrentTrack);
if (currentTrackIndex != null)
{
Playlist.CurrentTrack = (int)currentTrackIndex;
}
ApplicationSettingsHelper.SaveSettingsValue(BackgroundAudioConstants.BackgroundTaskState, BackgroundAudioConstants.BackgroundTaskRunning);
deferral = taskInstance.GetDeferral();
}
catch
{
}
}
/// <summary>
/// Fires when a message is recieved from the foreground app
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
void BackgroundMediaPlayer_MessageReceivedFromForeground(object sender, MediaPlayerDataReceivedEventArgs e)
{
foreach (string key in e.Data.Keys)
{
switch (key.ToLower())
{
case BackgroundAudioConstants.PingBackground:
Debug.WriteLine("Received Ping from foreground"); // App is suspended, you can save your task state at this point
ValueSet message = new ValueSet();
message.Add(BackgroundAudioConstants.PingBackground, DateTime.Now.ToString());
BackgroundMediaPlayer.SendMessageToForeground(message);
break;
case BackgroundAudioConstants.AppSuspended:
Debug.WriteLine("App suspending"); // App is suspended, you can save your task state at this point
foregroundAppState = ForegroundAppStatus.Suspended;
ApplicationSettingsHelper.SaveSettingsValue(BackgroundAudioConstants.CurrentTrack, Playlist.CurrentTrackIndex);
break;
case BackgroundAudioConstants.AppResumed:
Debug.WriteLine("App resuming"); // App is resumed, now subscribe to message channel
foregroundAppState = ForegroundAppStatus.Active;
break;
case BackgroundAudioConstants.StartPlayback: //Foreground App process has signalled that it is ready for playback
Debug.WriteLine("Starting Playback");
StartPlayback();
break;
case BackgroundAudioConstants.UpdatePlaylist:
Debug.WriteLine("Updating playlist...");
Playlist.UpdatePlaylist();
break;
case BackgroundAudioConstants.ResetPlaylist:
var arg = new object();
if (e.Data.TryGetValue(BackgroundAudioConstants.ResetPlaylist, out arg))
{
Playlist.ResetCollection((int)arg);
}
break;
case BackgroundAudioConstants.AddTrack:
object track = new object();
if (e.Data.TryGetValue(BackgroundAudioConstants.AddTrack, out track))
{
// We should have the newest playlist with the new track already. If so, just repopulate the playlist.
Playlist.AddTracks(AudioBackgroundInterface.DeserializeAudioTracks(track.ToString()) as List <BackgroundTrackItem>);
}
break;
case BackgroundAudioConstants.PlayTrack: //Foreground App process has signalled that it is ready for playback
Debug.WriteLine("Starting Playback");
Object obj = new Object();
if (e.Data.TryGetValue(BackgroundAudioConstants.PlayTrack, out obj))
{
string s = obj as string;
if (!string.IsNullOrEmpty(s))
{
int t = Convert.ToInt32(s);
Playlist.PlayTrack(t);
}
}
break;
case BackgroundAudioConstants.RestorePlaylist: //Foreground App process updated List Track
Debug.WriteLine("Restoring ListTrack");
Playlist.PopulatePlaylist();
var currentTrack =
ApplicationSettingsHelper.ReadSettingsValue(BackgroundAudioConstants.CurrentTrack);
if (currentTrack == null)
{
break;
}
Playlist.CurrentTrack = (int)currentTrack;
break;
case BackgroundAudioConstants.SkipNext: // User has chosen to skip track from app context.
Debug.WriteLine("Skipping to next");
SkipToNext();
break;
case BackgroundAudioConstants.SkipPrevious: // User has chosen to skip track from app context.
Debug.WriteLine("Skipping to previous");
SkipToPrevious();
break;
}
}
}
