如何实现带背景的镂空文字

[self addSubview:self.underDescribeTitleLabel];
    [self addSubview:self.describeTitleLabel];

-(void)setRank:(NSUInteger) rank
{
    _rank = rank;
    UIColor *strokeColor = BGColorHex(C69116);
    NSUInteger tempRank = rank/10+1;
    if(0 == rank)
    {
        tempRank = 0;
    }
    else if(rank >= 100)
    {
        tempRank = 10;
    }
    switch (tempRank) {
        case 0:
            strokeColor = BGColorHex(A1A1A1);
            break;
        case 1:
            strokeColor = BGColorHex(FE7241);
            break;
        case 2:
            strokeColor = BGColorHex(FF9802);
            break;
        case 3:
            strokeColor = BGColorHex(FFBF01);
            break;
        case 4:
            strokeColor = BGColorHex(CBDC3C);
            break;
        case 5:
            strokeColor = BGColorHex(699E38);
            break;
        case 6:
            strokeColor = BGColorHex(26A99C);
            break;
        case 7:
            strokeColor = BGColorHex(05A8F3);
            break;
        case 8:
            strokeColor = BGColorHex(4F6BEA);
            break;
        case 9:
            strokeColor = BGColorHex(663CB5);
            break;
        case 10:
            strokeColor = BGColorHex(E9407B);
            break;
            
        default:
            break;
    }
    
    NSString *rankStr = [NSString stringWithFormat:@"%lu", rank];
    NSString *str = [NSString stringWithFormat:@"fron%@", rankStr];
    NSUInteger fillCharacterCount = 4;
    NSMutableAttributedString *textAttributedString = [[NSMutableAttributedString alloc] initWithString:str];
    [textAttributedString addAttribute:NSForegroundColorAttributeName value:[UIColor clearColor] range:NSMakeRange(0, fillCharacterCount)];
    [textAttributedString addAttribute:NSStrokeColorAttributeName value:strokeColor range:NSMakeRange(fillCharacterCount, rankStr.length)];
    [textAttributedString addAttribute:NSStrokeWidthAttributeName value:@4.0 range:NSMakeRange(fillCharacterCount, rankStr.length)];
   [textAttributedString addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:12.f] range:NSMakeRange(0, fillCharacterCount)];
   [textAttributedString addAttribute:NSFontAttributeName value:[UIFont boldSystemFontOfSize:12.f] range:NSMakeRange(fillCharacterCount, rankStr.length)];
    self.describeTitleLabel.attributedText = textAttributedString;
    [self.describeTitleLabel updateLayout];
    
    textAttributedString = [[NSMutableAttributedString alloc] initWithString:str];
    [textAttributedString addAttribute:NSForegroundColorAttributeName value:[UIColor clearColor] range:NSMakeRange(0, fillCharacterCount)];
    [textAttributedString addAttribute:NSForegroundColorAttributeName value:[UIColor whiteColor] range:NSMakeRange(fillCharacterCount, rankStr.length)];
    [textAttributedString addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:12.f] range:NSMakeRange(0, fillCharacterCount)];
    [textAttributedString addAttribute:NSFontAttributeName value:[UIFont boldSystemFontOfSize:12.f] range:NSMakeRange(fillCharacterCount, rankStr.length)];
    self.underDescribeTitleLabel.attributedText = textAttributedString;
    [self.underDescribeTitleLabel updateLayout];
    
    
    NSString *filename = [NSString stringWithFormat:@"lv%lu", tempRank];
    self.decribeImageView.image = [UIImage imageNamed:filename];
}