Question

DirectoryEntry testAD = new DirectoryEntry();    
DirectorySearcher search = new DirectorySearcher(testAD);

StringBuilder add = new StringBuilder();
search.PropertiesToLoad.Add("mail");
search.Filter = "(&(objectClass=user))";

foreach (SearchResult SearchAll in search.FindAll())
{
    DirectoryEntry de = SearchAll.GetDirectoryEntry();
    add.Append(de.Properties["mail"].Value.ToString()); // error message here
}

PrefixDescription.Text = add.ToString();

I’m trying to find all emails first as a test and then all information (first name, last name, etc) and list it in a text box using a LPAR filter but I keep getting this error message when I run the app:

Object reference not set to an instance of an object.

Answer 1

Well, you’re enumerating users – but you have no guarantee that the resulting user will have an e-mail address! You need basic “programming 101” error prevention:

.....
foreach (SearchResult result in search.FindAll())
{
    // this is totally unnecessary - the "SearchResult" already *contains* all
    // the properties you've defined in your "PropertiesToLoad" collection!
    // DirectoryEntry de = SearchAll.GetDirectoryEntry();

    if(result.Properties["mail"] != null && result.Properties["mail"].Count > 0)
    {
        add.Append(result.Properties["mail"][0].ToString());
    }
}

With this extra check, you avoid the Object reference not set.... error…