Error when trying to tap on LongListSelector - windows-phone-8

Question

I've made a JumpList (by following this tutorial) linked with a LongListSelector, but I can't redirect the user when he taps on an item of the list. I used to do it well with a simple LongListSelector as this one :
<phone:LongListSelector x:Name="lls_Songs" SelectionChanged=lls_Songs_SelectionChanged>
<phone:LongListSelector.ItemTemplate>
<DataTemplate>
<StackPanel Margin="5,5,5,5">
<TextBlock Text="{Binding Name}" FontSize="30"/>
<TextBlock Text="{Binding Duration}" FontSize="20" Opacity="0.75"/>
</StackPanel>
</DataTemplate>
</phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>
But now I use this code...
<phone:LongListSelector
x:Name="lls_songs"
Margin="12,35,12,0"
Visibility="Visible"
JumpListStyle="{StaticResource JumpListStyle}"
Background="Transparent"
GroupHeaderTemplate="{StaticResource lls_SongsHeaderTemplate}"
ItemTemplate="{StaticResource lls_SongsTemplate}"
LayoutMode="List"
IsGroupingEnabled="true"
SelectionChanged="lls_songs_SelectionChanged"
HideEmptyGroups ="true"/>
...linked with this code :
<DataTemplate x:Key="lls_SongsTemplate">
<StackPanel VerticalAlignment="Top" Orientation="Horizontal" Margin="5,5,5,5">
<StackPanel Orientation="Vertical">
<toolkit:ContextMenuService.ContextMenu>
<toolkit:ContextMenu>
<toolkit:MenuItem Header="détails"/>
<toolkit:MenuItem Header="ajouter à la lecture"/>
</toolkit:ContextMenu>
</toolkit:ContextMenuService.ContextMenu>
<TextBlock Text="{Binding songName}" FontSize="30" />
<TextBlock Text="{Binding songArtist}" FontSize="20" Opacity="0.75"/>
</StackPanel>
</StackPanel>
</DataTemplate>
here is the lls_Songs_SelectionChanged method :
private void lls_songs_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
Song _selectedSong = lls_songs.SelectedItem as Song;
MediaPlayer.Play(_selectedSong);
}
and finaly how I create my songs list :
MediaLibrary _library = new MediaLibrary();
List<MusicInfo> MusicInfoList = new List<MusicInfo>();
int so = _library.Songs.Count;
int _so = 0;
while(_so < so)
{
Song _song = null;
_song = _library.Songs[_so];
MusicInfoList.Add(new MusicInfo(_song.Name, _song.Artist.ToString()));
_so = _so + 1;
}
linked with this class:
public string songName { get; set; }
public string songArtist { get; set; }
public MusicInfo(string _songName, string _songArtist)
{
this.songName = _songName;
this.songArtist = _songArtist;
}
and the jumplist :
private void SortingSongsListsAZ()
{
List<AlphaKeyGroup<MusicInfo>> DataSource = AlphaKeyGroup<MusicInfo>.CreateGroups(MusicInfoList,
System.Threading.Thread.CurrentThread.CurrentUICulture,
(MusicInfo s) => { return s.songName; }, true);
lls_songs.ItemsSource = DataSource;
}
And when I tap on an item of the list, I get this error : "This method does not accept null for this parameter". I don't understand why, anyone would help me ?

Answer 1

Share or check your lls_songs items source binding and code. from your code it appears that
Song _selectedSong = lls_songs.SelectedItem as Song;
_selectedSong is null.
in debug mode see what is the value of SelectedItem. is it Song type or something else?

Answer 2

According to your update, it seems that lls_songs.SelectedItem is of type MusicInfo instead of Song. Fixing your type-casting should remove the error I believe :
MusicInfo _selectedSong = lls_songs.SelectedItem as MusicInfo;
Or better yet this way :
MusicInfo _selectedSong = (MusicInfo)lls_songs.SelectedItem;