Correct implementation of IGrouping to be used inside longlistselector groupheader - linq

Question

I have an ObservableCollection like the following-
private ObservableCollection<KeyedList<int, Anime>> _grp;
public ObservableCollection<KeyedList<int, Anime>> GroupedAnimeByGenre
{
get
{
return _grp;
}
set
{
_grp = value;
RaisePropertyChanged("GroupedAnimeByGenre");
}
}
I am using this to populate a LongListSelector with grouping. The KeyedList is implemented like this-
public class KeyedList<TKey, TItem> : List<TItem>
{
public TKey Key { protected set; get; }
public KeyedList(TKey key, IEnumerable<TItem> items)
: base(items)
{
Key = key;
}
public KeyedList(IGrouping<TKey, TItem> grouping)
: base(grouping)
{
Key = grouping.Key;
}
}
I have the following code to feed the ObservableCollection. Keep in mind AnimeList2 is a temporary Collection.
var groupFinale = AnimeList2.GroupBy(txt => txt.id).Where(grouping => grouping.Count() > 1).ToObservableCollection();
GroupedAnimeByGenre = groupFinale ;
But I am unable to convert/use groupFinale with GroupedAnimeByGenre. I am missing the extension method part as I am not well aware of the syntax. Please help

Answer 1

If you remove the ToObservableCollection() call and take just that part
var groupFinale = AnimeList2.GroupBy(txt => txt.id).Where(grouping => grouping.Count() > 1);
you'll see that the type of groupFinale is IEnumerable<IGrouping<int, Anime>>. Hence applying ToObservableCollection() will result in ObservableCollection<IGrouping<int, Anime>>. However, the type of the GroupedAnimeByGenre is ObservableCollection<KeyedList<int, Anime>>. So you need to convert IEnumerable<IGrouping<int, Anime>> to IEnumerable<KeyedList<int, Anime>> which in LINQ is performed by the Select method.
Shortly, you can use something like this
var groupFinale = AnimeList2
.GroupBy(txt => txt.id)
.Where(grouping => grouping.Count() > 1)
.Select(grouping => new KeyedList<int, Anime>(grouping))
.ToObservableCollection();
You can make such conversion easier by providing an extension method (similar to BCL provided ToArray() / ToList()) that will allow skipping the type arguments like this
public static class KeyedList
{
public static KeyedList<TKey, TItem> ToKeyedList<TKey, TItem>(this IGrouping<TKey, TItem> source)
{
return new KeyedList<TKey, TItem>(source);
}
}
Then you can use simply
var groupFinale = AnimeList2
.GroupBy(txt => txt.id)
.Where(grouping => grouping.Count() > 1)
.Select(grouping => grouping.ToKeyedList())
.ToObservableCollection();