asp.net DirectoryEntry error

I'm trying bind the entry from the first dropdownlist (AD domain selection) to populate a second dropdownlist with a list of user 'cn'.

The complier error message: BC30311: Value of Type 'String' cannot be converted to 'System.DirectoryServices.DirectoryEntry'

Line 51: Dim adEntry As DirectoryEntry = adStrng
Visual studio also flags that 'dropdownlist1' is not declared within Public Function EumerateDomainUsers()

Imports System
Imports System.Data
Imports System.Linq
Imports System.IO
Imports System.DirectoryServices
Imports System.DirectoryServices.AccountManagement
Imports System.DirectoryServices.ActiveDirectory
Imports System.Security
Imports System.Security.Permissions
Imports System.Text
Imports System.Collections
Imports System.ComponentModel
Imports System.Drawing
Imports System.Web
Imports System.Web.SessionState
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.HtmlControls
 
Partial Class _Default
    Inherits System.Web.UI.Page
 
    Public Function EnumerateDomains() As ArrayList
        Dim alDomains As New ArrayList()
        Dim currentForrest As Forest = Forest.GetCurrentForest()
        Dim myDomains As DomainCollection = currentForrest.Domains
        For Each objDomain As Domain In myDomains
            alDomains.Add(objDomain.Name)
        Next
        Return alDomains
    End Function
 
    Protected Sub Selection_Changed(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Me.Load
        DropDownList1.Items.Clear()
        DropDownList1.AppendDataBoundItems = True
        DropDownList1.SelectedIndex = 0
        DropDownList1.DataSource = EnumerateDomains()
        DropDownList1.DataBind()
        'Dim dUsers As String = DropDownList1.SelectedItem.ToString()
    End Sub
 
    Public Function EumerateDomainUsers() As ArrayList
        Dim domainUsers As New ArrayList()
        Dim usr As String
        'Dim fqdns As String = DropDownList1.SelectedItem.ToString()
        Dim fqdns As String = DropDownList1.SelectedItem.Text
        Dim adStrng As String = "LDAP://" & fqdns
        Dim adEntry As DirectoryEntry = (adStrng)
        Dim searcher As DirectorySearcher = New DirectorySearcher(adEntry)
        searcher.Sort.PropertyName = "cn"
        Dim results As SearchResultCollection
        Dim result As SearchResult
        searcher.PropertiesToLoad.Add("cn")
        results = searcher.FindAll
        For Each result In results
            usr = result.GetDirectoryEntry().Properties("cn").Value
            domainUsers.Add(usr)
        Next
        Return domainUsers
    End Function
 
    Protected Sub Selection_Changed1(ByVal sender As Object, _
  ByVal e As System.EventArgs) Handles Me.Load
        DropDownList2.Items.Clear()
        DropDownList2.AppendDataBoundItems = True
        DropDownList2.SelectedIndex = 0
        DropDownList2.DataSource = EumerateDomainUsers()
        DropDownList2.DataBind()
        'Dim dUsers As String = DropDownList1.SelectedItem.ToString()
    End Sub
End Class

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patelbg2001Asked:
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Peter HutchisonSenior Network Systems SpecialistCommented:
Try changing this line from:
49: Dim adEntry As DirectoryEntry = (adStrng)
to
49: Dim adEntry As DirectoryEntry = GetObject(adStrng)
0
patelbg2001Author Commented:
The change returned the following error. the page began to load, is it better to getobject as a separate function?

Unable to cast COM object of type 'System.__ComObject' to class type 'System.DirectoryServices.DirectoryEntry'. Instances of types that represent COM components cannot be cast to types that do not represent COM components; however they can be cast to interfaces as long as the underlying COM component supports QueryInterface calls for the IID of the interface.

Description: An unhandled exception occurred during the execution of the
current web request. Please review the stack trace for more information about the error and where it originated in the code. 



Exception Details: System.InvalidCastException: Unable to cast COM object of type 'System.__ComObject' to class type 'System.DirectoryServices.DirectoryEntry'. Instances of types that represent COM components cannot be cast to types that do not represent COM components; however they can be cast to interfaces as long as the underlying COM component supports QueryInterface calls for the IID of the interface.
0
Peter HutchisonSenior Network Systems SpecialistCommented:
Oops, I was thinking of ActiveDS.IADsUser objects, try this syntax:

49:  Dim adEntry As DirectoryEntry = New System.DirectoryServices.DirectoryEntry(adStrng)
0

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Steve813Commented:
I'm a C# guy so I hope I get the VB.Net syntax right here...

Line 57 should be changed.  You already have the "cn" in the SearchResult variable of "result" and this can be accessed via the Properties.  Change line 57 to:

usr = result.Properties("cn").Value
0
patelbg2001Author Commented:
I try suggested in the morning.
Is c# more flexible for coding directory services in asp.net than vb?
0
Peter HutchisonSenior Network Systems SpecialistCommented:
In C#: the syntax would be similar:

DirectoryEntry adEntry;
adEntry = new DirectoryEntry(adStrng);
or
adEntry = new System.DirectoryServices.DirectoryEntry(adStrng);
0
patelbg2001Author Commented:
it's now picked up another error

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
Line 47:         Dim usr As String
Line 48:         'Dim fqdns As String = DropDownList1.SelectedItem.ToString()
Line 49:         Dim fqdns As String = DropDownList1.SelectedItem.Text
Line 50:         Dim adStrng As String = "LDAP://" & fqdns
Line 51:         'Dim adEntry As DirectoryEntry = GetObject(adStrng)

Stack Trace:
[NullReferenceException: Object reference not set to an instance of an object.]
   _Default.EumerateDomainUsers() in D:\ADConnect\Default.aspx.vb:49
   _Default.Selection_Changed1(Object sender, EventArgs e) in D:\ADConnect\Default.aspx.vb:71
   System.EventHandler.Invoke(Object sender, EventArgs e) +0
   System.Web.UI.Control.LoadRecursive() +70
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3177
0
Peter HutchisonSenior Network Systems SpecialistCommented:
Looks like you missed the 'new' statement for line 51 to create a new instance of object type DirectoryEntry.

Dim adEntry As DirectoryEntry = New DirectoryEntry(adStrng)
0
patelbg2001Author Commented:
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

The error was at line 49
Line 49:         Dim fqdns As String = DropDownList1.SelectedItem.Text

Line51:  was commented out & ignored.
0
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