This might be happening because prepareForSegue is getting called before didSelectRowAtIndexPath:. Here is what I would do:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if ([segue.identifier isEqualToString:@"nextView"]) {
DetailEventViewController *myVC = [segue destinationViewController];
NSIndexPath *selectedIndexPath = [self.tableView indexPathForSelectedRow];
myVC.tituloEvento = [nomeEvent objectAtIndex:selectedIndexPath.row];
}
}