I found a new problem: when I implement dynamic category select drop down, the sub category works well, but when I push refresh/reset/clear filter, the sub category select cann`t return the original select. What should I do?
Thank you for explanation. Now it's clear what you mean. Probably some seaching parameters are need be reseted before staring grid reload. I recommend you to look at this old answer which describe how search criteria (filter) can be cleared. You can do this for example inside your custom beforeRefresh event handler. I hope it will work.
I have currently no working example which dynymicylly populate select dropdown list and work per ajax. Another example which implement the same locally you can find here. I hope it could help you a litle.