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Thread: Creating, storing and managing forms dynamically

  1. #1

    Thread Starter
    Junior Member
    Join Date
    Apr 2009
    Posts
    19

    Creating, storing and managing forms dynamically

    Hi, I'm making a LAN instant messenger and I'm trying to achieve something similar to how MSN will open a new chatting window when you double click on a friend. My main form has a list of friends, and I want to create a new chat window when they double click on one of those friends. I've created a "template" chat form which I want to generate dynamically, and I've run into some problems I need help with. Lets look at the code I already have.

    The sub for double clicking on the friend listbox:
    Code:
        Private Sub lbFriends_DoubleClick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lbFriends.DoubleClick
           Dim fd() As String = Split(My.Settings.Friends.Item(lbFriends.SelectedIndex), "|"c)
            If lbFriends.SelectedIndex >= 0 Then
                If IsInClientList(fd(0)) = False Then
                    Me.Invoke(New del(AddressOf OpenNewChat))
                End If
                'Connection code
            End If
        End Sub
    The sub for creating a new chat window, adding it to a list, and showing it:
    Code:
        Private Sub OpenNewChat()
            Dim NewChatWind As New ClientWind
            CWL.Add(ClientWind)
            CWL.Item(CWL.Count - 1).Show()
        End Sub
    And outside of those subs I have this:
    Code:
        Private Delegate Sub del()
        Dim CWL As New List(Of ClientWind)
    The form will only appear once as far as I can tell, and the chat form has events such as button clicks; an error occurs when I try to change something like the text property of a label for example (eg. clicking a button on the chat form changes the text of a label on the chat form will cause an error to occur). The error I actually get is:

    Cross-thread operation not valid: Control 'ClientWind' accessed from a thread other than the thread it was created on.
    Now, call me a newb if you will, but I really don't know much about threading and all that hocus pocus. Some guidance in the right direction would be great.

    EDIT: ClientWind is the chat form.
    EDIT: That's weird. It doesn't occur with the actual builds.
    Last edited by PSYCHONAUT; Jan 20th, 2011 at 03:56 PM.

  2. #2
    .NUT jmcilhinney's Avatar
    Join Date
    May 2005
    Location
    Sydney, Australia
    Posts
    102,567

    Re: Creating, storing and managing forms dynamically

    Cross-thread calls are allowed in a Release build but, by default, not in a Debug build. Follow the Codebank link in my signature and check out my submission on Accessing Controls From Worker Threads.

    That said, it sounds like you're creating your chat windows on a different thread, which bad, bad, bad. You use Invoke in your code but you don;t show where you're creating new threads, so it's hard tro say where the issue is.

  3. #3

    Thread Starter
    Junior Member
    Join Date
    Apr 2009
    Posts
    19

    Re: Creating, storing and managing forms dynamically

    I managed to solve the issue by invoking components on the chat form when necessary, but it's a bit of a hassle.

    You use Invoke in your code but you don;t show where you're creating new threads, so it's hard tro say where the issue is.
    Well I'm not 100% sure what you're asking, but the OpenNewChat sub is located under the same class as the lbFriends_DoubleClick sub if that means anything.

    EDIT: BTW, I can still only get one instance of the chat window to open, it has something to do with the fact I'm adding them to a list. When I do it without the list, it will show multiple instances as expected. Any ideas?

    EDIT: Never mind, it was a stupid little mistake. Notice I had "CWL.Add(ClientWind)" instead of "CWL.Add(NewChatWind)".
    Last edited by PSYCHONAUT; Jan 20th, 2011 at 06:54 PM.

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