如果目录条目不存在

在 asp.net c# 中使用目录条目，如果我调用：

ADUtils newAdClass = new ADUtils("dl-dom", "ad.test", "Password?1");
    List<string> domUsers = newAdClass.GetDomainUsers();
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public List<string> GetDomainUsers()
{
    //returned list
    List<string> domainUsers = new List<string>();
    //create connection
    DirectoryEntry entry = new DirectoryEntry(_lDAPPath, _ldapUser, _ldapPassword);
    DirectorySearcher search = new DirectorySearcher(entry);
    //search subtree nodes
    search.SearchScope = SearchScope.Subtree;
    //Active Directory LDAP: All email users (alternate)
    search.Filter = "(&(objectClass=user)(objectcategory=person))";
    //create results objects from search object 
    SearchResultCollection results = search.FindAll();
    //run through list, for each entry remove 'CN=' and add 'user' to list
    for (int i = 0; i < results.Count; i++)
    {
        DirectoryEntry de = results[i].GetDirectoryEntry();
        string user = de.Name.Replace("CN=", "");
        domainUsers.Add(user);
    }
    return domainUsers;
}

但是，在测试用户是否输入不存在的域时，这工作正常。

例如

ADUtils newAdClass = new ADUtils("FAKE-dl-dom", "ad.test", "Password?1");

这在我的代码中抛出了一个错误，所以我试图使用http://msdn.microsoft.com/en-us/library/system.directoryservices.directoryentry.exists%28v=vs.110%29.aspx存在

但是目录条目返回一个对象，当我需要测试字符串时，我认为路径是错误的......有什么想法吗？

string entry1 = _lDAPPath + "," + _ldapUser + "," + _ldapPassword;
//entry1 returns: LDAP://DC=dl-dom,ad.test,Password?1
if (DirectoryEntry.Exists(entry1))
{
    DirectorySearcher search = new DirectorySearcher(entry);

当我使用上面的代码时，我得到异常

An invalid dn syntax has been specified.

构造 函数：

public ADUtils(string LDAPDomain, string ADUser, string ADUserPwd)
{
    _lDAPPath = "LDAP://DC=" + LDAPDomain;
    _ldapUser = ADUser;
    _ldapPassword = ADUserPwd;
}

try
{
    //create results objects from search object 
    SearchResultCollection results = search.FindAll();
    //run through list, for each entry remove 'CN=' and add 'user' to list
    for (int i = 0; i < results.Count; i++)
    {
        DirectoryEntry de = results[i].GetDirectoryEntry();
        string user = de.Name.Replace("CN=", "");
        domainUsers.Add(user);
    }
}
catch(Excpetion e)
{
    //add code here to process the error
    //after debugging, you may even decide to just swallow the exception 
    // and return an empty collection
}