帮我解释一下这个??是什么意思,
protected SortedList AnsweredQuestions
{
get { return (SortedList)(ViewState[ "AnsweredQuestions "] ?? new SortedList()); }
set { ViewState[ "AnsweredQuestions "] = value; }
}
[解决办法]
??
这个符号在vs2005里头才有的,,是判断是否为可空类型!