title: What is the best way to check if my UIView has already been shown?
body: <p>what is the best way to check if my UIView has already been shown on the screen. I have UISplitViewController in which I tried to display details in custom UIView after tap on tableViewCell. All I wanna do is to avoid duplication of the view that has already been displayed, or if possible closure of the present and display the new one. </p>
  
  <pre><code>- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
  NSLog(@"did select row at index path %ld",(long)indexPath.row );
  InvoiceDetailsVC *detailsVC = [[InvoiceDetailsVC alloc]initWithFrame:CGRectMake(321, 0,708, 709)];
  
   //here I would like to check if my detailsVC has already been shown 
   //if not I would like to display in that way
   [self.splitViewController.view addSubview:detailsVC];
  }
  </code></pre>
  
  <p>Thanks for any help
  Regards</p>