Implement Custom Sorting

By default, RadListBox sorts items by their Text property. This article will show you how to implement custom sorting - the items will be sorted by their Value property.

For this purpose, we will use the IComparer interface which exposes a method that compares two objects.

Here are the two steps that you need to perform:

• Create a class that implements IComparer for your custom sorting:

public class SortListBoxItemsByValue : IComparer
{
    public int Compare(object x, object y)
    {
        RadListBoxItem p1 = new RadListBoxItem();
        RadListBoxItem p2 = new RadListBoxItem();
        if (x is RadListBoxItem)
            p1 = x as RadListBoxItem;
        else
            throw new ArgumentException("Object is not of type RadListBoxItem.");
        if (y is RadListBoxItem)
            p2 = y as RadListBoxItem;
        else
            throw new ArgumentException("Object is not of type RadListBoxItem.");
        int cmp = 0;
        if (p1.ListBox.Sort == RadListBoxSort.Ascending)
        {
            //here we compare the Values of the items
            cmp = String.Compare(p1.Value, p2.Value, !p1.ListBox.SortCaseSensitive);
        }
        if (p1.ListBox.Sort == RadListBoxSort.Descending)
        {
            //here we compare the Values of the items
            cmp = String.Compare(p1.Value, p2.Value, !p1.ListBox.SortCaseSensitive) * -1;
        }
        return cmp;
    }
}

Public Class SortListBoxItemsByValue
    Implements IComparer
    Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer
        Dim p1 As New RadListBoxItem()
        Dim p2 As New RadListBoxItem()
        If TypeOf x Is RadListBoxItem Then
            p1 = TryCast(x, RadListBoxItem)
        Else
            Throw New ArgumentException("Object is not of type RadListBoxItem.")
        End If
        If TypeOf y Is RadListBoxItem Then
            p2 = TryCast(y, RadListBoxItem)
        Else
            Throw New ArgumentException("Object is not of type RadListBoxItem.")
        End If
        Dim cmp As Integer = 0
        If p1.ListBox.Sort = RadListBoxSort.Ascending Then
            'here we compare the Values of the items
            cmp = [String].Compare(p1.Value, p2.Value, Not p1.ListBox.SortCaseSensitive)
        End If
        If p1.ListBox.Sort = RadListBoxSort.Descending Then
            'here we compare the Values of the items
            cmp = [String].Compare(p1.Value, p2.Value, Not p1.ListBox.SortCaseSensitive) * -1
        End If
        Return cmp
    End Function
End Class

• Call the overloaded Items.Sort methods passing your IComparer as a parameter:

RadListBox1.Sort = RadListBoxSort.Ascending;
RadListBox1.Items.Sort(new SortListBoxItemsByValue());

RadListBox1.Sort = RadListBoxSort.Ascending
RadListBox1.Items.Sort(New SortListBoxItemsByValue())

That's it. Now the ListBox items will be sorted by their Value instead of Text property.