Controls not populated when form loaded for second time - vb.net

Question

I've got a program which calls a second form. This second form has a combo box populated from the contents of an external file, and the user needs to select an option in the combo box from the presented options. This selection is then passed back to the main form where a lot of work is done.
This all works nicely the first time it is done. However, the second time this second form is called, the drop-down is blank. I've confirmed via some debugging that the correct code is being run and that entries are being added via "SecondForm.ComboBox1.Items.Add" (I can clear the combobox, check it's zero, read the data and then check the items in the list again, it increases correctly) but they're just not being displayed on the form. I can't figure out why or how to fix it.
And so the pertinent parts of the code....
At the form level I have this line to set up the second form, I believe I need the WithEvents to pass the selected data back as far as I can tell:
Public Class Form1 Friend WithEvents SecondForm As New Form2
Public Sub OpenStripformatstxtToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles OpenStripformatstxtToolStripMenuItem.Click
Dim fd As OpenFileDialog = New OpenFileDialog()
Dim pos1 As Integer
Dim pos2 As Integer
' Select the file to open
fd.Title = "Open File Dialog"
fd.InitialDirectory = "C:\BEST\Data"
fd.Filter = "Text files (*.txt)|*.txt|All files (*.*)|*.*"
fd.FilterIndex = 1
fd.RestoreDirectory = True
' Put the filename selected in strfilename2
If fd.ShowDialog() = DialogResult.OK Then
strFileName2 = fd.FileName
Else : Return
End If
If SecondForm.IsDisposed Then
Dim secondform As New Form2
I suspect this line above is the problem, I'm creating the form a second time but WITHOUT the WithEvents paramater. However I can't use that from within this part of the code, I get an error "'WithEvents' is not a valid local variable declaration". I've read that closing and reopening forms is not good coding and that I should be hiding / showing them
secondform.Show()
InitializeComponent()
Else
SecondForm.Show()
End If
' Copy the file contents to a string called sfcontents (Strip Format Contents)
sfcontents = My.Computer.FileSystem.ReadAllText(fd.FileName)
' Define some points in the string, starting at the beginning
pos1 = 1
pos2 = 1
' Loop from the start to the end of the string
For pos1 = 1 To Len(sfcontents)
' Look for FO, the strip name header, do the following if you find it
If Mid(sfcontents, pos1, 3) = "FO " Then
pos1 = pos1 + 3
pos2 = pos1 + 1
'Find the space after "FO " so we've captured the whole next word, that's the strip name
Do Until Mid(sfcontents, pos2, 1) = " "
pos2 = pos2 + 1
Loop
' Add that strip name to the combobox for selecting by user
SecondForm.ComboBox1.Items.Add(Mid(sfcontents, pos1, pos2 - pos1))
It is this line above which is populating the ComboBox, but that data is NOT being displayed on the form which is shown to the user after the first instance of the form is shown
End If
' Next step in the string
Next pos1
End Sub
Private Sub secondform_formclosing(sender As Object, e As FormClosingEventArgs) Handles SecondForm.FormClosing
There's a few hundred lines of code in here which then work with the data passed from the form closing, ie the selected value of the ComboBox. This all works fine for the first running of the code, but as the ComboBox is empty on subsequent runs, it doesn't work after that. Happy to post that code if anyone thinks it'll help, but I think it'll just muddy the issue at this stage as that code seems fine. However, see the bit below about event handlers...
End Sub
The code on Form2.vb is as follows:
Public Class Form2
Public selectedstrip As String '= ComboBox1.SelectedItem
Public stripfunction As Integer
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If RadioButton1.Checked Then stripfunction = 1
If RadioButton2.Checked Then stripfunction = 2
If RadioButton3.Checked Then stripfunction = 3
selectedstrip = ComboBox1.SelectedItem
Me.Close()
End Sub
End Class
I've read a bit online that says closing and reopening forms is not, excuse the pun, good form. However I'd then need event handlers for form.hide and I can't seem to work out how to use them or even what they are. If hiding the form is a better alternative solution, if someone could point me in the right direction for how to do that and what handlers to use instead, then I'd be grateful.
I'm probably doing something incredibly stupid, because everything I'm doing is self-taught from googling and I probably lack a greater understanding of WHY I need to do certain things, so apologies for any ignorance on my part. With that in mind, if I'm doing anything a completely silly way I'm open to rewriting it in a way that helps, but I may need some hand-holding to do that!
Thanks in advance for any help anyone can give.

Answer 1

The main problem appears to he here:
If SecondForm.IsDisposed Then
Dim secondform As New Form2
You are declaring a new local variable there and assigning the new Form2 object to that rather than the member variable, so when you later refer to the member variable to populate the ComboBox, you're not referring to the Form2 instance you just created.
Your code is rather weird anyway. Here's my advice.
Firstly, get rid of the code form Form1 that populates the ComboBox in Form2. Forms should populate their own controls. Put the code to populate the ComboBox in the Load event handler of Form2. You're then guaranteed that any time you call Show on a new instance of Form2, the code to populate the ComboBox will be executed. That's how a form should work.
As an alternative, given that you're reading from a file and that data probably won't change over the course of a session, read the data and put it into an array in Load event handler of Form1 and then pass that array to the constructor of Form2. You would have to write that constructor yourself and, in it, you would populate the ComboBox with the array data. That way, you're not reading and processing the same data file over and over but you're still populating Form2's controls in Form2.
Secondly, change this code:
If SecondForm.IsDisposed Then
Dim secondform As New Form2
secondform.Show()
InitializeComponent()
Else
SecondForm.Show()
End If
to this:
If SecondForm.IsDisposed Then
'Create and display a new instance.
Secondform = New Form2
Secondform.Show()
Else
'Focus the existing instance.
SecondForm.Activate()
End If
Note that there is no local variable, so the new instance is assigned to the member variable.
There is also no call to InitializeComponent. That method is what creates and configures the controls on a form based on the actions in the designer. The ONLY place that gets called is in a constructor.
Finally, if an instance of Form2 is already displayed, its Activate method is called to make sure that it has focus.