如何使用C＃通过用户名搜索Active Directory？

我正在尝试通过用户名 admin搜索活动目录。我知道一个事实，即目录中有一个使用该用户名的用户，但是搜索一直没有返回。

I'm trying to search active directory by the username 'admin'. I know for a fact that there is a user with that username in the directory, but the search keeps coming back with nothing.

var attributeName = "userPrincipalName";
var searchString = "admin"
var ent = new DirectoryEntry("LDAP://"dc=corp,dc=contoso,dc=com")
var mySearcher = new DirectorySearcher(ent);
mySearcher.Filter = string.Format("(&(objectClass=user)({0}={1}))", attributeName, searchString);

var userResult = mySearcher.FindOne();

userResult总是以null结尾，我很想知道为什么，在那里

userResult always ends up null. I would love to know why, there must be something that I'm missing.