[Typo3] Sorting problem in my own extension

[Piotr Burda]

I wrote a simple adress list extension.
It works fine, but i can`t sort by town

some lines from extension :
   // Initializing the query parameters:
 
list($this->internal["orderBy"],$this->internal["descFlag"]) = 
explode(":",$this->piVars["sort"]);
 
$this->internal["results_at_a_time"]=t3lib_div::intInRange($lConf["results_at_a_time"],0,1000,20); 
                // Number of results to show in a listing.
 
$this->internal["maxPages"]=t3lib_div::intInRange($lConf["maxPages"],0,1000,2);; 
                // The maximum number of "pages" in the browse-box: 
"Page 1", "Page 2", etc.
 
$this->internal["searchFieldList"]="name,zip,town,street,phone,contact,branch,province,www,email";
$this->internal["orderByList"]="uid";


i changed uid to town in last line but it doesn't work too.

Where is the problem?