Regarding Multi sorting in AW.UI.Grid

Hi,

I have a grid(AW.UI.Grid) with 4 columns. When ever the column header is clicked the corresponding column should be sorted. But for 4th column, when ever a user clicks the 4th column header, the column should be sorted, but also want to sort the 1st column. The result must be based on 1st column.

Please help me

AW implements stable sorting, so the user can just click on 1st column and then 4th column to get the desired result.