Postback is a problem

I had quite a few headaches when playing with postback, sometimes the
criteria was lost while the result was not refreshed during the other
times. For the time being my system managed to work, but this is
"programming by coincidence", because I didn't really understand how
postback works.

It seems, we should check whether the page IsPostBack() at the very
beginning of the event handler of Page_Load() and then go on proceeding
with other initializing method. Otherwise, user input will be overrided.