validation in datalist

hi all
i have a datalist in which i m showing some products that have a textbox
for quantity. And in prallel i have a dropdownlist with each product.
Now i want a validation that validate textbox like that atleat one textbox have some value
and respectively dropdown have some salection.
( If one of these textbox have some value then it will not validate all the text box)
Hi, check whether this article -DataGrids and Validationhelps...