dynamic change theme using datanase?

Hi there

I use C# write preInit as follow to set theme dynamically by dropdownlist
and it is working for me, but how can I get theme from database first time
and second time using dropdownlist value(+ save into database)? any good
suggestion for this logic?

Thanks

void Page_PreInit(object sender,EvengArgs e)
{
this.Theme=Request["DropdownList"].ToString();
}


Tony Dong