UIActivityIndicatorView *indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
indicator.hidesWhenStopped = YES; // 끝나면 사라지도록...
[self.tableView addSubview:indicator];
indicator.center = self.tableView.center; // indicator를 화면 중앙에 표시하기.
[indicator setBackgroundColor:[UIColor whiteColor]]; // inidicator의 배경색상 지정(기본값은 투명).

[indicator startAnimating];
// to do...
[indicator stopAnimating];
[indicator release];