php pdo save query data
: Call to a member function rowCount() on a non-object in C:wampwwwprjyclassesuser.php on line 34

$this->sth = $this->dbh->prepare("SELECT id, userlevel FROM users WHERE username = ? AND password = ?");
$this->sth->bindParam(1, $username);
$this->sth->bindParam(2, $password);
$this->data = $this->sth->execute();

if ($this->data->rowCount() > 0)

count($this->data)

$stmt1 = $this->dbh->prepare( /* first select statement */ );
$stmt1->bindParam(1, $username);
$stmt1->bindParam(2, $password);

$stmt2 = $this->dbh->prepare( /* second select statement */ );
$stmt2->bindParam(1, $username);
$stmt2->bindParam(2, $password);

if( $stmt1->execute() && $stmt2->execute() )
{
    if( $stmt1->rowCount() > 0 )
    {
        $result = $stmt1->fetchAll();
    }
    else if( $stmt2->rowCount() > 0 )
    {
        $result = $stmt2->fetchAll();
    }
}

$db = new PDO(
          'dsn connection string',
          'username',
          'password',
          array( PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true )
      );

$this->sth = $this->dbh->prepare("SELECT id, userlevel FROM users WHERE username = ? AND password = ?");
$this->sth->bindParam(1, $username);
$this->sth->bindParam(2, $password);
if($this->data = $this->sth->execute()) {
   if ($this->data->rowCount() > 0) {
      // do something here ..
   }
}

if (!$this->data = $this->sth->execute()) { echo "ERROR!"; print_r($this->sth->errorInfo()); die(); }