UIPickerView去掉背景上的黑線

- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(nullable UIView *)view;
{
    UILabel* pickerLabel = (UILabel*)view;
    if (!pickerLabel){
        pickerLabel = [[UILabel alloc] init];
        pickerLabel.font=[UIFont systemFontOfSize:18 weight:1];
        pickerLabel.textColor=[UIColor whiteColor];
        pickerLabel.textAlignment=1;
        [pickerLabel setBackgroundColor:[UIColor clearColor]];
    }
    pickerLabel.text=[self pickerView:pickerView titleForRow:row forComponent:component];
    //在該代理方法里添加以下兩行代碼刪掉上下的黑線
    [[pickerView.subviews objectAtIndex:1] setHidden:TRUE];
    [[pickerView.subviews objectAtIndex:2] setHidden:TRUE];
    return pickerLabel;
}