Question

I think I know what the problem is, but I have no clue as to the solution to it.

I have an observable collection which i populate in a WPF DataGrid.
I have then implemented Drag and Drop for rows in the DataGrid to child grids.
If a row is dragged to another grid I change a value in the ObservableCollection and then display
the underlying data like this:

                var q = from standard in DispatchResult
                        where DispatchResult.Route == RouteName
                        select standard;

                dgRoutedData.ItemsSource = q;

I guess that me setting the itemssource to the result of the above LINQ query breaks the whole auto notification from the observable collection, so how do I get the datagrids to show filtered views that will actually update when items have their “Route” value changed?

Answer 1

You need to notify that the change has occurred – you can always try wrapping the result of the linq query in a new ObservableCollection

e.g.

var col = new ObservableCollection<DispatchResult>();
col.AddRange(q);
dgRoutedData.ItemsSource = col;

(this has the disadvantage that you need to operate on the new observable as the previous observable wont raise item changed events for the new observable)

Or just clearing/and re-adding to the existing collection.

I assume though you’ve avoided this because the original collection contains items that you want to filter ‘back-in’ after you’ve removed the filter. In this case you might want to keep a private backing field to hold the actual data, and use ObservableCollection<T> as a filtered window onto that backing field.

e.g.

_myList = new List<MyObject>(); // Populate it etc
SomeObservable.Clear(); 
SomeObservable.AddRange(from item in _myList where item.ID == 1 select item);

Or dont re-invent the wheel and use PagedCollectionView as someone suggested which wraps the above functionality (a private backing field with a filter predicate and other functionality baked in)