Column headers can display filter buttons. Clicking a filter button invokes a filter dropdown, which lists unique values within a column,
and enables you to apply filter criteria against this column.
By default, these buttons are hidden. To show filter buttons, set the Settings.ShowHeaderFilterButton property to true.
The ASPxGridView allows you to create custom filter values, define a filter criteria for them and display these values within a column's filter dropdown.
To do this, handle the HeaderFilterFillItems event. In this demo, custom filter values are displayed within the 'Total' and 'Quantity' columns'
filter dropdowns.