iOS富文本和html字符串互转

//html字符串转换为富文本NSString *htmlStr = @"我的<span style='color:red'>aafaf微</span>我的<span style='color:red'>aafaf微</span>";    NSAttributedString *att = [[NSAttributedString alloc] initWithData:[htmlStr dataUsingEncoding:NSUnicodeStringEncoding] options:@{NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType} documentAttributes:nil error:nil];    //富文本转换为html(最后相当于整个网页代码，会有css等)    NSDictionary *dic = @{NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType,                 NSCharacterEncodingDocumentAttribute:@(NSUnicodeStringEncoding)};    NSData *data = [att dataFromRange:NSMakeRange(0, att.length) documentAttributes:dic error:nil];    NSString *str = [[NSString alloc] initWithData:data encoding:NSUnicodeStringEncoding];