/**
* process a task only one page
* @param integer $id task id
* @return none
*/
public function work($id)
{
// get task infomation
$task = $this->_db->query("select * from task where `id`={$id}");
$task = $task->fetch_array();
$count = $task['count'];
$page = $task['page'] + 1;
$id = $task['id'];
// get new data
parent::__construct($task['keyword'], $page);
$data = $this->results();
// fill data into database
$this->datain($data, $id);
// update task infomation
$count += count($data);
$this->_db->query("update `task` set `page`={$page} ,`count`={$count} where id={$id}");
}