[iOS] Show UIActivityIndicatorView

UIActivityIndicatorView

UIActivityIndicatorView *activityIndicatorView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
activityIndicatorView.frame = CGRectMake(0.0f, 0.0f, 40.0f, 40.0f);
activityIndicatorView.center = self.view.center;
[self.view addSubview:activityIndicatorView];
[activityIndicatorView bringSubviewToFront:self.view];
[activityIndicatorView startAnimating];
[UIApplication sharedApplication].networkActivityIndicatorVisible = TRUE;