Question

Ok I think I’m doing something wrong here.

I am using a PagedCollectionView mapped to an ObservableCollection of a custom type. I want to be able to manually sort the underlying collection whenever the user tries to sort a DataGrid column.

I did the following:

    obs = new ObservableCollection<Seats>(arrSeats);
    view = new PagedCollectionView(obs);

    INotifyCollectionChanged sortchangeNotifier = view.SortDescriptions as INotifyCollectionChanged;
    sortchangeNotifier.CollectionChanged += new NotifyCollectionChangedEventHandler(sortchangeNotifier_CollectionChanged);
    grdData.ItemsSource = view;

    void sortchangeNotifier_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        // What to do here?
    }

The event handler is being correctly invoked whenever the column header is clicked. However, whenever I try to modify the ObservableCollection, I get the following exception:

Cannot change or check the contents or current position of the PagedCollectionView while Refresh is being deferred.

I want to be able to implement my own custom sorting algorithm. Any ideas?

Thanks!

EDIT

Well, this is particularly crazy, but when I wrap my code with a try/catch block in the event handler method, the changes are actually applied. Any ideas 🙂 ?

Answer 1

The problem you really wanted to solve was having custom sorting of a PagedCollectionView —

“I am using a PagedCollectionView mapped to an ObservableCollection of a custom type. I want to be able to manually sort the underlying collection whenever the user tries to sort a DataGrid column.”

Customizing/Extending the PagedCollectionView is the way to do this. When I had the need to do the same I created a dictionary of IComparer

public Dictionary<string, IComparer<object>> CustomSortFunctions
    {
        get
        {
            if (this.customSortFunctions == null)
            {
                this.customSortFunctions = new Dictionary<string, IComparer<object>>();
            }
            return this.customSortFunctions;
        }
    }

such that the key of each pair is intended to correspond to a DataGridColumn.SortMemberPath. For any column for which you desire custom sorting you add a suitable value pair.

To leverage this dictionary modify the SortList method of PagedCollectionView to check for a custom comparer to sort by (and then sort in the applicable direction). For instance:

if (this.CustomSortFunctions.ContainsKey(description.PropertyName))
{
    source = source.OrderBy(a => a, this.CustomSortFunctions[description.PropertyName]);
}

As a user “sorts” with the data grid your desired sorting will occur.

Your starting point is the PagedCollectionView — the source for which is included in the overall the source code for the Silveright Toolkit (in Toolkit/Systems.Windows.Data/PagedCollection).