[ListGrid] How to display all sorted columns' arrow and sequence

[garywu]

I use SmartGWT v2.2, and my code invoke ListGrid setCanMultiSort(true).
When I click grid header it sort normally, but I can't see any result from ListGrid's getSortNumeralHTML().

I need getSortNumeralHTML() to display all sorted column, please HELP me HOW to do this, THANKS A LOT.