iOS OC富文本内部图片宽等于控件宽高度自适应

 CGFloatwidth =  (SCREEN_WIDTH-30);

    NSString*str  = [NSString stringWithFormat:@"%@",model.introduction];

    NSString *detailTextString = [NSString stringWithFormat:@"img{width:%f !important;height:auto}%@",width,str];

    NSAttributedString *attributedStr = [[NSAttributedString alloc]initWithData:[detailTextString dataUsingEncoding:NSUnicodeStringEncoding]options:@{ NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType} documentAttributes:nil error:nil];

_discribeLabel.attributedText = attributedStr;