ICollectionView Sort doesn't work after changing source

Question

I have a method that queries a database using entity framework and places the results in an ICollectionView. The ICollectionView acts as the ItemsSource for a DataGrid. Everything works fine on the first query, but upon querying a second time, the data is not properly sorted, despite the application of the correct SortDescriptions.

Here is my code for trying querying and grouping/sorting the data:

    CollectionViewSource cvsRS;

    private ObservableCollection<productorder> rs;
    public ObservableCollection<productorder> RS
    {
        get { return rs; }
        set
        {
            if (rs != value)
            {
                rs = value;
                OnPropertyChanged("RS");
            }
        }
    }

    private ICollectionView rsView;
    public ICollectionView RSView
    {
        get { return rsView; }
        set
        {
            if (rsView != value)
            {
                rsView = value;
                OnPropertyChanged("RSView");
            }
        }
    }

    public void QueryDatabase()
    {

        RS = new ObservableCollection<productorder>(DatabaseEntities.productorders.Where(o => o.month.id == CurrentMonth.id));
        if (RS != null)
        {
            cvsRS.Source = RS;
            RSView = cvsRS.View;

            RSView.GroupDescriptions.Clear();
            RSView.GroupDescriptions.Add(new PropertyGroupDescription("producttype.productcategory.name"));
            RSView.GroupDescriptions.Add(new PropertyGroupDescription("producttype.name"));  

            RSView.SortDescriptions.Clear();
            RSView.SortDescriptions.Add(new SortDescription("producttype.productcategory.sortorder", ListSortDirection.Ascending));
            RSView.SortDescriptions.Add(new SortDescription("client.name", ListSortDirection.Ascending));
            RSView.Refresh();
            CurrentRecord = null;
            SelectedRecords = null;
        }
    }

The grouping works fine, but the groups aren't in the correct order based on the sorting. I've tried a number of possible "fixes" with no success (e.g. adding sort/group descriptions directly to the CollectionViewSource, sorting before grouping, removing some of the sorting/grouping, removing the SortDescriptions per CollectionViewSource does not re-sort on property change).

Does anyone know how to maintain the sort order regardless of how many queries are performed? I'm open to alternative methods of querying displaying the data in the DataGrid if that may work.

I'd try binding the Source (not assign, bind, using an instance of the `Binding` class) once, to an `ObservableCollection` property which raises `PropertyChanged` when you give it a new collection. Then repopulate by changing the property. Either toss in a new collection, or clear and repopulate the old one. But don't ever touch `cvsRS.Source` except to set up the `Binding` initially. — 15ee8f99-57ff-4f92-890c-b56153, Oct 31 '16 at 14:40
Hopefully I interpreted this correctly, I did this in my constructor: `cvsRS = new CollectionViewSource(); cvsRS.Source = new Binding("RS"); RSView = cvsRS.View;` But I get an error: 'System.Windows.Data.Binding' is not a valid value for property 'Source'. — matthew_b, Oct 31 '16 at 14:53
I whipped up a quick test and it worked as I expected, so I posted an answer with an example of how to do the binding. Pasting that into a comment would be unreadable anyhow. — 15ee8f99-57ff-4f92-890c-b56153, Oct 31 '16 at 15:16

15ee8f99-57ff-4f92-890c-b56153 · Accepted Answer · 2016-10-31T15:25:14.243

Try binding your CollectionViewSource.Source property to your ObservableCollection<T> property. Set up the binding in the viewmodel constructor. Then, just leave it alone. Update the ObservableCollection<T>, replace it, etc. As long as it's an ObservableCollection<T> and its public property raises PropertyChanged whenever you replace it, the whole thing will work.

public MyViewModel()
{
    BindCollectionViewSource();
}

protected void BindCollectionViewSource()
{
    cvsRS = new CollectionViewSource();

    var binding = new Binding
    {
        Source = this,
        Path = new PropertyPath("RS")
    };
    BindingOperations.SetBinding(cvsRS, CollectionViewSource.SourceProperty, binding);
}

//  Since we're not going to be messing with cvsRS or cvsRS.View after the 
//  constructor finishes, RSView can just be a plain getter. The value it returns 
//  will never change. 
public ICollectionView RSView
{
    get { return cvsRS.View; }
}

You can't just assign a binding to Source; there's more to it than that. The Source="{Binding RSView}" stuff you see in XAML may look like an assignment, but some details are being hidden for convenience. The Binding actively does stuff. It needs to know who the target object is.

I did see one funny thing: I gave my test code one PropertyGroupDescription and one SortDescription. When I added items to the collection, it sorted them within the groups. Then when I called RSView.Refresh(), it resorted them without reference to the groups. Not sure I understood what it was doing there.

Thanks Ed. I've implemented the code above, but my `DataGrid` never shows any data now. Its `ItemsSource` is bound to `RSView`. I also kept my `QueryDatabase` method identical, with the exception of removing `cvsRS.Source = RS; RSView = cvsRS.View;` — matthew_b, Oct 31 '16 at 15:53
Just for now try RS.Clear() and Add items to it, instead of creating a new collection. — 15ee8f99-57ff-4f92-890c-b56153, Oct 31 '16 at 15:54
@matthew_b Ohhhh -- another thing I forgot, may need RSView.Refresh() when stuff changes. — 15ee8f99-57ff-4f92-890c-b56153, Oct 31 '16 at 16:01
Yes, it is necessary (just tested it), though I already had that implemented. Thanks again. — matthew_b, Oct 31 '16 at 16:12

ICollectionView Sort doesn't work after changing source

1 Answers1