ios富文本行间距

1.如果设置段落NSMutableParagraphStyle 行间距，在只有一行文字时需要不设置行间距lineSpacing，否则会出现文字在控件中不居中展示
2.富文本获取文字高度需要在最后拼上一个换行符\n
例

    NSDictionary *attribute = @{NSFontAttributeName:font,NSParagraphStyleAttributeName:paragraphStyle};
    NSString *displayStr = [self stringByAppendingString:@"\n"];
    CGFloat height = [displayStr boundingRectWithSize:size
                                              options:
                      NSStringDrawingTruncatesLastVisibleLine |
                      NSStringDrawingUsesLineFragmentOrigin |
                      NSStringDrawingUsesFontLeading
                                           attributes:attribute context:nil].size.height;