WPF DataGrid CustomSort for each Column

Question

I have a WPF DataGrid bound to a CollectionViewSource that encapsulates an ObservableCollection. This CollectionViewSource has two main objectives:

1) To group each

Answer 1

I changed @trilson86's answer so that you need only one custom sorter-class for the whole DataGrid.

First the Interface:

public interface ICustomSorter : IComparer
{
    ListSortDirection SortDirection { get; set; }

    string SortMemberPath { get; set; }
}

Next the Bevaviour-class which defines the CustomSorterProperty in such way that you can use it directly on the DataGrid, not on the DateGridRow. In HandleCustomSorting() the property SortMemberPath of the CustomSorter ist filled with the actual value from the clicked column, you can use this value in your CustomSorter to sort against the desired column.

public class CustomSortBehaviour
{
    #region Fields and Constants

    public static readonly DependencyProperty CustomSorterProperty =
        DependencyProperty.RegisterAttached("CustomSorter", typeof (ICustomSorter), typeof (CustomSortBehaviour));

    public static readonly DependencyProperty AllowCustomSortProperty =
        DependencyProperty.RegisterAttached("AllowCustomSort",
            typeof (bool),
            typeof (CustomSortBehaviour),
            new UIPropertyMetadata(false, OnAllowCustomSortChanged));



    #endregion

    #region public Methods

    public static bool GetAllowCustomSort(DataGrid grid)
    {
        return (bool) grid.GetValue(AllowCustomSortProperty);
    }


    public static ICustomSorter GetCustomSorter(DataGrid grid)
    {
        return (ICustomSorter)grid.GetValue(CustomSorterProperty);
    }

    public static void SetAllowCustomSort(DataGrid grid, bool value)
    {
        grid.SetValue(AllowCustomSortProperty, value);
    }


    public static void SetCustomSorter(DataGrid grid, ICustomSorter value)
    {
        grid.SetValue(CustomSorterProperty, value);
    }

    #endregion

    #region nonpublic Methods

    private static void HandleCustomSorting(object sender, DataGridSortingEventArgs e)
    {
        var dataGrid = sender as DataGrid;
        if (dataGrid == null || !GetAllowCustomSort(dataGrid))
        {
            return;
        }

        var listColView = dataGrid.ItemsSource as ListCollectionView;
        if (listColView == null)
        {
            throw new Exception("The DataGrid's ItemsSource property must be of type, ListCollectionView");
        }

        // Sanity check
        var sorter = GetCustomSorter(dataGrid);
        if (sorter == null)
        {
            return;
        }

        // The guts.
        e.Handled = true;

        var direction = (e.Column.SortDirection != ListSortDirection.Ascending)
            ? ListSortDirection.Ascending
            : ListSortDirection.Descending;

        e.Column.SortDirection = sorter.SortDirection = direction;
        sorter.SortMemberPath = e.Column.SortMemberPath;

        listColView.CustomSort = sorter;
    }

    private static void OnAllowCustomSortChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var existing = d as DataGrid;
        if (existing == null)
        {
            return;
        }

        var oldAllow = (bool) e.OldValue;
        var newAllow = (bool) e.NewValue;

        if (!oldAllow && newAllow)
        {
            existing.Sorting += HandleCustomSorting;
        }
        else
        {
            existing.Sorting -= HandleCustomSorting;
        }
    }

    #endregion
}

You can use it in XAML like this: