play music on windows phone 8.1 - windows-phone-8.1

Question

I tried to get all the music files into listbox and play the selected file.
The below code is what i did to play music but unfortunately it doesn't play. Can anyone tell me what the mistake is?
private async void button1_Click(object sender, RoutedEventArgs e)
{
StorageFolder folder = Windows.Storage.KnownFolders.MusicLibrary;
IReadOnlyList<StorageFile> files = await folder.GetFilesAsync();
foreach (var file in files)
{
MusicProperties music = await file.Properties.GetMusicPropertiesAsync();
listBox2.Items.Add(music.Title);
}
}
private async void listBox2_Tapped(object sender, TappedRoutedEventArgs e)
{
try
{
StorageFolder folder = Windows.Storage.KnownFolders.MusicLibrary;
IReadOnlyList<StorageFile> files = await folder.GetFilesAsync();
if (files.Count > 0)
{
var file = files[listBox2.SelectedIndex];
mediaElement1.Source = new Uri(files[listBox2.SelectedIndex].Path);
textBlock1.Text = files[listBox2.SelectedIndex].Path;
mediaElement1.Play();
}
}
catch(Exception ex)
{
textBlock1.Text = ex.Message;
}
}

Answer 1

Instead mediaElement1.Source = new Uri(files[listBox2.SelectedIndex].Path); you need use the code bellow:
var fileStream = await file.OpenReadAsync();
mediaElement.SetSource(fileStream, file.ContentType);

Answer 2

You need to use BackgroundMediaPlayer with background task.
MSDN
You can write apps for Windows Phone 8.1 that play audio in the background. This means that even after the user has left your app by pressing the Back button or the Start button on their device, your app can continue to play audio.
Scenarios for background audio playback include:
Long-running playlists The user briefly brings up a foreground app to select and start a playlist, after which the user expects the playlist to continue playing in the background.
Using task switcher The user briefly brings up a foreground app to start playing audio, then switches to another open app using the task
switch. The user expects the audio to continue playing in the
background.