iPhone：如何在UIPickerView中隐藏滚动指示器

Question

我在UIPickerView中使用UITextField来显示图片和文本。当在选择器中滚动时，垂直滚动指示器显示出来。我怎么能让它消失？

- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row
      forComponent:(NSInteger)component reusingView:(UIView *)view{

      UITextField *field = (UITextField*) view;

      if (view == nil) {

          field = [[[UITextField alloc] initWithFrame:CGRectMake(0, 0, 280, 44)]autorelease];
          field.backgroundColor = [UIColor clearColor];   // overriding highlighted selection
          field.delegate = self; 

      }
      ...