iOS UILabel UITextView UIButton 等等显示文本行间距都用如下方法
NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
paragraphStyle.lineSpacing = 5;// 字体的行间距
NSDictionary *attributes = @{NSFontAttributeName:[UIFont systemFontOfSize:15],NSParagraphStyleAttributeName:paragraphStyle};
label.attributedText = [[NSAttributedString alloc] initWithString:self.showDetailView.text attributes:attributes];