cocoll 0 Junior Poster in Training

hello!
i need help with custom validator,so when i have a requiredfiledvalidator for a textbox which autopostback=true ,so if the textbox is empty then i saw the error message,but with custom validator it doesn't work even when i place a button and i click on it so it doesn't work or to be cleared sometimes worked and then no :(.
but i need for the custom validator to work in autopostback property of the textbox not when i oress a button and i want that this custom validator to be sure that the textbox is not empty.
so i need help .
thank you.