I receive this error message while trying to run this procedure: "The type or namespace name 'Generic' does not exist in the class or namespace 'System.Collections' (are you missing an assembly reference?)"

I get a null reference exception for this line:

 ctl = ctls.First.Value;

 When I try to use that code. Any ideas why? Thanks.
 

I've been through something similar a few times myself so I can probably help you. Before I try that, however, please give me the following information so I can customize an answer to your question:

(1) VB or C#?   (2) The code for your control and what you want to find.

Nice Answer For the Find Control Problem

good job

A couple more variations that may help you.  They both use generics to return a specific type of control.

'Find first instance of a control:
Private Shared Function FindControlIterative(Of T As Control)(ByVal root As Control, ByVal id As String) As T
    Dim ctl As Control = root
    Dim ctls As LinkedList(Of Control) = New LinkedList(Of Control)

    Do While (ctl IsNot Nothing)
        If ctl.ID = id Then
            Return ctl
        End If
        For Each child As Control In ctl.Controls
            If child.ID = id Then
                Return child
            End If
            If child.HasControls() Then
                ctls.AddLast(child)
            End If
        Next
        ctl = ctls.First.Value
        ctls.Remove(ctl)
    Loop

    Return Nothing
End Function

'Build collection of controls with matching ID (useful if root is a GridView control for example):
Private Shared Function FindControlCollection(Of T As Control)(ByVal root As Control, ByVal id As String) As List(Of T)
    Dim ctl As Control = root
    Dim ctls As LinkedList(Of Control) = New LinkedList(Of Control)
    Dim ControlCollection As New List(Of T)

    Do While (ctl IsNot Nothing)
        If ctl.ID = id Then
            ControlCollection.Add(ctl)
        End If
        For Each child As Control In ctl.Controls
            If child.ID = id Then
                ControlCollection.Add(child)
            End If
            If child.HasControls() Then
                ctls.AddLast(child)
            End If
        Next
        If (ctls.Count > 0) Then
            ctl = ctls.First.Value
            ctls.Remove(ctl)
        Else
            ctl = Nothing
        End If
    Loop

    Return ControlCollection
End Function

Could you please provide a C# version of the code since I am not familiar with VB?

Thanks.

Are you working in VB or C#? Also, write what you've tried to do so far so I and other people can get an idea of what you need and the names of some of your variables and controls. In this way, the response you receive can be more personalized to your needs.

The whole idea is that when you go looking for Bill or John or Dave in a college dorm hall, you will get so many answers as to confuse you. You want to compartmentalize your search on a per-room basis in the dorm. Applying this to a Visual Studio project, you can more or less give the same name to various child controls (such as textboxes, buttons, etc.) contained in different parent controls (such as a CreateUserWizard, DetailsView, GridView, etc.), by knowing from which dorm room in the project you can find the control.

Excuse me, but everytime I look at this particular thread, it looks different. I wonder if a bunch of posts are being thrown into this thread mistakenly. I've seen it happen before.

@david wendelken

I like it when people break it down this way. You tend to get less questions. Anyway this method wont be used in every case but will go in my toolbox when needed. I will most likely use it every now and then.

 Thanks.

 Hi ks2007

It may be to late now but here it goes.

You can write a helper class witch contains the FindControl method then in code behind you do the following:

//Invoke a new instance of your helper class
FindControls findControl = new FindControls();

    this assumes that your helper class is named FindControls.

then you simply in stead of running FinControl() framework method you run following

Label label= findControl.FindControlByID(Page.Controls, "ControlName") as Label;

findControl = new instance of your helper class

FindControlByID(Page.Controls, "ControlName") = the method in your helper class

now you have a "new" label control in you code behind called label... you can use it like this. 

label1.Text = label.Text; ...just like any other label control in your app.  

Unless you're creating controls dynamically that you need to find later, or you're drilling into a grid that's populated with a datasource, might it be useful to iterate once when a page is first built, and store some of that information in state? Where would the best place be to intercept the page build: Application_PreSendContent? Page_Unload? Has anyone done this?