Forcing a secondary sort on a DataGrid

Question

Is there an approach for programatically applying WPF DataGrid sorting based on multiple properties?

I have a multi-column DataGrid which contains a single column which I always want to be in alphabetical order within groupings of values when other columns are sorted.

All custom sort implementations I've seen use a IComparer, but this only provides the values in the single column it's associated with.

For example, if we have the following two columns of unsorted data:

• A 1
• D 2
• C 2
• B 1

If we apply sorting to the second column, the first column becomes arbitrarily sorted within each grouping:

• A 1
• B 1
• D 2
• C 2

What I am looking for is for within any groups of identical values in the second column, the first column is alphabetised:

• A 1
• B 1
• C 2
• D 2

Is there an alternative to IComparer which exposes the full model?

Answer 1

Have you looked into SortMemberPath?

<DataGrid.Columns>
    <DataGridTextColumn Header="Some Caption"  Width="200"
        CanUserSort="True"
        Binding="{Binding SomeDataField}" 
        SortMemberPath="OtherNonShowingField"/>
</DataGrid.Columns>

So if you are listing data from a List or from a DataTable via its DataColumn reference, you could always add another field or column that has the combined A + B parts in that field. So even if you don't show the column, it can be used as the basis of a sort.

Since I do not know of another way to utilize the SortMemberPath to do both an ascending AND descending in the same, I wrote a function that you can try to use in your code. I called it NegativeString, thus a reversal of alphabetical order and numbers. Anything else is "as-is".

private static string UpperCase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
private static string LowerCase = "abcdefghijklmnoprqstuvwxyz";
private static string Numbers = "0123456789";
public string NegativeString( string incoming )
{
    // take incoming string, put into a character array
    var inB = incoming.ToCharArray();
    var outStr = "";
    for( var i= 0; i < inB.Length; i++ )
    {
        // So, if I Look for "A" in the upper-case string, it is found
        // in position 0, so I want the character 0 from the end
        // which is the letter Z and vice-versa.
        var atPos = UpperCase.IndexOf(inB[i]);
        if (atPos > -1)
            outStr += UpperCase.Substring(UpperCase.Length - atPos - 1, 1);
        else
        {
            // if not upper case, then look for lower
            atPos = LowerCase.IndexOf(inB[i]);
            if (atPos > -1)
                outStr += LowerCase.Substring(LowerCase.Length - atPos - 1, 1);
            else
            {
                // if not lower, try numbers
                atPos = Numbers.IndexOf(inB[i]);
                if (atPos > -1)
                    outStr += Numbers.Substring(Numbers.Length - atPos - 1, 1);
                else
                    // anything else comes along as-is
                    outStr += inB[i];
            }
        }
    }

    return outStr;
}

So, a new property on your class could be something like

public string YourMultiSortProperty
{  get { return NormalField + NegativeString( OtherField ); }}