Passing Data from TableView to ViewController

I'm trying to send data from a table view to a viewController but it keeps crashing. Here is what i have done:

in prepare for segue

if ([segue.identifier isEqualToString:@"detailSegue"]){
    DetailView *dv = [segue destinationViewController];
    NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
    dv.stringForFirstLabel = [_cell.firstArray objectAtIndex:indexPath.row]
 }

but it logs this

: unrecognized selector sent to instance.