I have the same problem. I create multiple parameters for each category. But it is not always good idea because in some cases we tend to have 10 -15 categories.
I would love to see if there is any workaround where in have 1 drop down to select category and another text box to enter value.
i don't think it is possible.
Thanks for the reply Satish. After a few more days of trying, I still haven't managed to find a good solution as well.