windows phone 8 download and play audio on background - windows-phone-8

Question

I'm using background file transfer and background audio player.
in the TransferStatusChanged event i save the file to the isolated storage then play it with the audio player,
It works fine if the application is active and i want to do the same if the application is not active.

Answer 1

In WP8.0 it isn't possible as your TransferStatusChanged is in your App process which is stopped when you navigate away from it:
When the user navigates forward, away from an app, after the Deactivated event is raised, the operating system will attempt to put the app into a dormant state. In this state, all of the application’s threads are stopped and no processing takes place, but the application remains intact in memory.
You can make it work under LockScreen by disabling IdleDetection but it won't work when your App is put into dormant/tombstoned state.
You may consider to start playing when you activate the App or put some logic in BAP where you can check for example upon TrackChange if the file was downloaded and then play it.
edit
thanks to #Romasz suggestion of use empty track to play while the file complete downloading
then in TrackChange i check if the file downloaded and remove it from the download queue -this can be done in the audio background- things work fine now. here is some code
private AudioTrack GetNextTrack(bool isStart = false)
{
AudioTrack track = null;
using (IsolatedStorageFile ISF = IsolatedStorageFile.GetUserStoreForApplication())
{
if (isStart)
{
currentSongIndex = -1;
}
currentSongIndex++;
if (currentSongIndex == _ProgressList.Count())
{
//currentSongIndex = 0;
return track;
}
if (ISF.FileExists("shared/transfers/" + _ProgressList[currentSongIndex].FileName))
{
var request = requests.Where(it => it.Key == _ProgressList[currentSongIndex].FileName).FirstOrDefault().Value;
if (request != null)
{
bool isDone = ProcessTransfer(request, _ProgressList[currentSongIndex].Directory);
if(!isDone )
{
if(request.BytesReceived > LastDownloadedSize)
{
NumberOfTrialsToLoadNextTrack = 0;
LastDownloadedSize = request.BytesReceived;
}
else
{
++NumberOfTrialsToLoadNextTrack;
}
}
}
}
else
{
++NumberOfTrialsToLoadNextTrack;
}
if (ISF.FileExists(_ProgressList[currentSongIndex].Directory+_ProgressList[currentSongIndex].FileName))
{
track = playList[currentSongIndex];
NumberOfTrialsToLoadNextTrack = 0;
LastDownloadedSize = 0;
}
else
{
currentSongIndex--;
if (NumberOfTrialsToLoadNextTrack < 10)
{
track = new AudioTrack(new Uri("halfsec.mp3", UriKind.Relative),
"empty",
"empty",
"empty",
null);
}
}
}
return track;
}
private bool ProcessTransfer(BackgroundTransferRequest transfer, string directory = "")
{
bool isDone = false;
switch (transfer.TransferStatus)
{
case TransferStatus.Completed:
if (transfer.StatusCode == 200 || transfer.StatusCode == 206)
{
RemoveTransferRequest(transfer.RequestId);
using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())
{
string filename = transfer.Tag;
System.Diagnostics.Debug.WriteLine(directory + filename);
if (isoStore.FileExists(directory + filename))
{
isoStore.DeleteFile(directory + filename);
}
if (isoStore.FileExists(transfer.DownloadLocation.OriginalString))
{
isoStore.MoveFile(transfer.DownloadLocation.OriginalString, directory + filename);
}
}
isDone = true;
}
else
{
RemoveTransferRequest(transfer.RequestId);
if (transfer.TransferError != null)
{
}
}
break;
}
return isDone;
// NotifyComplete();
}
private void RemoveTransferRequest(string transferID)
{
// Use Find to retrieve the transfer request with the specified ID.
BackgroundTransferRequest transferToRemove = BackgroundTransferService.Find(transferID);
// try to remove the transfer from the background transfer service.
try
{
BackgroundTransferService.Remove(transferToRemove);
}
catch (Exception)
{
}
}
protected override void OnPlayStateChanged(BackgroundAudioPlayer player, AudioTrack track, PlayState playState)
{
switch (playState)
{
case PlayState.TrackEnded:
player.Track = GetNextTrack();
break;
case PlayState.TrackReady:
player.Play();
break;
case PlayState.Shutdown:
// TODO: Handle the shutdown state here (e.g. save state)
break;
case PlayState.Unknown:
break;
case PlayState.Stopped:
break;
case PlayState.Paused:
break;
case PlayState.Playing:
break;
case PlayState.BufferingStarted:
break;
case PlayState.BufferingStopped:
break;
case PlayState.Rewinding:
break;
case PlayState.FastForwarding:
break;
}
NotifyComplete();
}
this code in the AudioPlayer class, the files added to the download queue in the xaml.cs normally