Filtering issue with ICollectionView

Question

ImageAlbums is an ICollectionView type and GlobalCollection.MyImageAlubms is an ObservableCollection<T> type.

ImageAlbums = CollectionViewSource.GetDefaultView(GlobalCollection.MyImageAlubms);
ImageAlbums.Filter = new Predicate<object>(this.FilterImageAlbumList);

In a view I'm using ImageAlbums for showing a filtered image list. I have filtered the list using FilterImageAlbumList method. The problem is I have used the GlobalCollection.MyImageAlubms in another place. In that view I have used the GlobalCollection.MyImageAlubms directly as source but in there the list are being showed as filtered also. I am also providing the filter method here, following code represents the filter method

private bool FilterImageAlbumList(object item)
{
    AlbumModel albumMoel = (AlbumModel)item;
    if(LOGIC_OF_FILTERING)
    {
        return false;
    }
    return true;
}

Is there any way to filter only ImageAlbums without affecting the GlobalCollection. FYI - I won't deep copy the Global Collection.

Since item is an object you can test the type. Each class has a different enumeration for type. — jdweng, Nov 29 '16 at 10:27
You can create a new view with `new CollectionViewSource { Source = GlobalCollection.MyImageAlubms}.View;` however I've found this buggy in the past (http://stackoverflow.com/questions/37166747/object-reference-not-set-to-an-instance-of-an-object-in-presentationframework) and ended up just creating copies... — Joe, Nov 29 '16 at 10:29
@lukai that's why I put it as a comment, not an answer. Just giving options. Someone else might suggest it as an answer without knowing it's faults. — Joe, Nov 29 '16 at 10:59

score 3 · Accepted Answer · answered Nov 29 '16 at 10:48

Your problem is caused by these two facts:

Each collection instance has only one default (instance of the) view, thus CollectionViewSource.GetDefaultView always returns the same instance for the same argument
WPF binding mechanism does not bind directly to a collection, but to its default collection view

So if you set a filter on the default view, its effects are visible wherever you bind to the collection.

If you want a separate instance of an ICollectionView your best bet is to instantiate it manually. For ObservableCollection<T> a good choice is ListCollectionView. So this should resolve your problems:

ImageAlbums = new ListCollectionView(GlobalCollection.MyImageAlubms);

Filtering issue with ICollectionView

1 Answers1