iOS UIPickerView 可能会出现选中行不显示或者去掉上下两条横线的问题解决，

- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view
{
    UILabel *label = [[UILabel alloc] init];
    label.frame = CGRectMake(0, 0, _picker.frame.size.width, 32);
    label.font = [UIFont systemFontOfSize:22];
    if (component == 0) {
        label.text = self.yearArray[row];
    }else if (component == 1) {
        label.text = self.monthArray[row];
    }else if (component == 2) {
        label.text = self.dayArray[row];
    }
    label.textAlignment = NSTextAlignmentCenter;
    
    //  设置横线的颜色，实现显示或者隐藏
    ((UILabel *)[_picker.subviews objectAtIndex:1]).backgroundColor = FINELINECOLOR;
    
    ((UILabel *)[_picker.subviews objectAtIndex:2]).backgroundColor = FINELINECOLOR;
    
    return label;
}