c#对象引用未设置为对象的实例

Question

如果表格中不存在某些内容,我正在努力解决问题.我告诉它,看看是否UserInfo包含信息user.

UserInfo Character = db.UserInfoes.SingleOrDefault(a => a.Username == user);
if (Character.Username == null || Character.Username.Length == 0)
{
    //do stuff
}

但是我在if声明中得到了错误.

你调用的对象是空的.

Answer 1

似乎db.UserInfoes.SingleOrDefault(a => a.Username == user)返回了表达式,null因为它找不到满足过滤条件的任何匹配记录.

所以:

UserInfo Character = db.UserInfoes.SingleOrDefault(a => a.Username == user);
if (Character == null || Character.Username == null || Character.Username.Length == 0)
{
    //do stuff
}