- (UIView*)subViewOfClassName:(NSString*)className {
 for (UIView* subView in self.subviews) {
  if ([NSStringFromClass(subView.class) isEqualToString:className]) {
   return subView;
  }

  UIView* resultFound = [subView subViewOfClassName:className];
  if (resultFound) {
   return resultFound;
  }
 }
 return nil;
}

UIView* backgroundView = [searchBar subViewOfClassName:@"_UISearchBarSearchFieldBackgroundView"];
backgroundView.layer.cornerRadius = 14.0f;
backgroundView.clipsToBounds = YES;