UIActivityIndicatorView居中

activityIndicator = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];activityIndicator.frame = CGRectMake(0.0, 0.0, 30.0, 30.0);//activityIndicator.center = self.view.center;activityIndicator.center = CGPointMake(160.0f, 208.0f);[self.view addSubview: activityIndicator];