Question

I have a series of methods being called for my networking code. An event gets fired from the networking thread. Inside this event, which I’ve hooked into from a singleton class, I route messages to form level methods which they register on form load to handle certain messages they care about. Inside of these form message hooks I need to close the current form (which I was able to do) but also show a different one (which is giving me the trouble).

The new form sort of shows but it’s hanging/not updating. I’m sure this has something to do with that form because it’s .Show() was basically called from another thread (sort of) doesn’t have a message loop, but I’m not sure how else to solve this. The network message that gets received indicates on the client machine what forms to close and show.

The flow might be confusing so I’ll try better to explain.

Login form attaches user defined functions inside that form to a singleton class list of messages. For example when a message called LOGIN_STATUS is fired I assign a function from the Login form to a list defined in this singleton class.

The singleton class has the network class defined in it which actually runs on another thread, but this is all handled inside the class. In the private ctor I subscribe to the OnData event of this network class.

When OnData gets fired from the network class to the singleton class it passes to it the type of data. I loop through the list of function pointers to see if any of them are linked to LOGIN_STATUS and if so call them. This will call the Login forms function. Inside that function I need to close the Login form and open the Lobby form. That’s when the Lobby form shows, but is hung up and not updating.

Hope that makes sense.

This is all being done in VB.NET where I have the “close when last form closed” setting on which is what I want. VB.NET also makes it easier to manage forms since I can just for formname.Show() instead of having to keep a list of the forms and manage them myself like in C# so if that’s still possible with the solution that would be ideal.

Answer 1

If you want to ensure all forms are created on the same thread, and hence the same message loop, use the main from’s Invoke method. The Form.Invoke and Form.BeginInvoke methods cause the code to run from the form’s message loop. BeginInvoke allows the event calling thread to return immediately, where-as Invoke blocks the event thread until the method is complete. It depends how time sensitive your code is.

Private Sub OpenFormEvent(sender As Object, e As EventArgs)
    If MainForm.InvokeRequired Then
        Dim args As Object() = {sender, e}
        MainForm.BeginInvoke(New EventHandler(AddressOf OpenFormEvent), args)
    Else
        Dim SecondForm As New Form()
        SecondForm.Show()
    End If
End Sub