You can handle the GcMultiRow.SortCompare event to provide custom sorting. This event occurs only when the GcMultiRow.VirtualMode property is set to false. This event occurs once for each pair of cells with the same cell index that are being sorted. It occurs only when the user clicks the column header cell with a ColumnHeaderCell.SortMode property value of Automatic, or when you call the Sort method in GcMultiRow. When this event occurs for a column header cell with a ColumnHeaderCell.SortMode property value of SortMode.Programmatic, you must display the sorting glyph yourself with the ColumnHeaderCell.SortGlyphDirection property.

This class is used for changing the sorting result of two values. You can get the two compared values from this class and then set the result. This allows you to control the sorting result. If the user changes the compared result, set System.ComponentModel.HandledEventArgs.Handled to true and then it will take effect.

System.Object
   System.EventArgs
      System.ComponentModel.HandledEventArgs
         GrapeCity.Win.MultiRow.SortCompareEventArgs

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

SortCompareEventArgs Members
GrapeCity.Win.MultiRow Namespace
SortCompare Event