设置text的行距

 NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];

        [paragraph setLineSpacing:13];

        NSMutableAttributedString *attributeStr = [[NSMutableAttributedString alloc] initWithString:string attributes:@{NSFontAttributeName : [UIFont systemFontOfSize:13], NSForegroundColorAttributeName : RGB(0x999999), NSParagraphStyleAttributeName : paragraph}];

        self.msgLab.attributedText = attributeStr;