cannot read from combo box to use as a variable in a sub-routine - vb.net

Question

I am trying to have a variable input come from a combobox. i had thought it would be a simpler task but i am stuck on this and would be grateful for some help.
i am working with pre-packaged code that connects to an API, connects to a server and does stuff. I am customizing it to do a few additional calculations, all of which now work fine, but the variables i use to perform those calcs, inside of one of the sub-routines, are hard coded, and i want to be able to read them in instead using a combobox. i had done this many times using VB6 and VBA, but i am new to vb.net (2010) and even though i have the combobox on my form, every reference to the selected number in the combobox ends up with an empty result
in a simpler application, like the one below, i am able to get the data from the combo box:
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim divisor As Integer
Dim res1 As Integer
If Int32.TryParse(ComboBox1.Text, divisor) Then
MsgBox(ComboBox1.Text)
Else
MsgBox("error" & ComboBox1.Text)
End If
res1 = divisor - 9
MsgBox(res1)
End Sub
End Class
Unfortunately the code i am working with is not cooperating with the code above. without posting all the code, here is the basic structure, maybe this will help you help me figure out where to write the code above so it will grab the value in the combobox where the 'divisor' in the sub13 (see below) will be the number from the combobox instead of it being hard coded
and every reference you see below to the combobox was 'auto-generated'. that is, once i placed the combobox on the form all of that code appeared.
Imports X.API
Public Class frmMain
Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
Public Sub New()
MyBase.New()
InitializeComponent()
End Sub
Protected Sub Dispose(ByVal disposing As Boolean)
End Sub
Private components As System.ComponentModel.IContainer
Friend WithEvents Panel1 As System.Windows.Forms.Panel
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
Me.ComboBox1 = New System.Windows.Forms.ComboBox()
Me.ComboBox1.FormattingEnabled = True
Me.ComboBox1.Location = New System.Drawing.Point(710, 117)
Me.ComboBox1.Name = "ComboBox1"
Me.ComboBox1.Size = New System.Drawing.Size(121, 21)
Me.ComboBox1.TabIndex = 3
End Sub
#End Region
#Region " Member Variables "
Private mTable As DataTable
#End Region
#Region " Form and Control Events "
Private Sub frmMain_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
End Sub
Private Sub frmMain_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
End Sub
Private Sub s1()
End Sub
Private Sub s2()
End Sub
Private Sub s3()
End Sub
Private Sub s4()
End Sub
#End Region
#Region " Operations "
Private Sub s5()
End Sub
Private Sub s6()
End Sub
Private Sub s7()
End Sub
Private Sub s8()
End Sub
#End Region
#Region " API Events "
Private Sub s8()
End Sub
Private Sub s9()
End Sub
Private Sub s10()
End Sub
Private Sub s11()
End Sub
Private Sub s12()
End Sub
#End Region
Private Sub s13()
Dim divisor As Integer = 1
'[this is where i want the divisor to draw from the combobox]
'so instead of "Dim divisor As Integer = 1"
i want "Dim divisor As Integer = contents of combobox
End Sub
' i have no idea why this code appears here
Friend WithEvents ComboBox1 As System.Windows.Forms.ComboBox
Private Class Item1
Public Sub s14()
End Sub
End Class
Private Class Item2
Public Sub s15()
End Sub
End Class
Private Class Item3
Public Sub s16()
End Sub
End Class
End Class
the sub i am working on is "s13()", but when i try to read from the combobox i get a blank.
exactly where to place the code that works as shown in my first example in the structure i show immediately above is unknown to me. i would have thought it would be much easier to read from a combobox, but i am stumped.

Answer 1

Given the names of your functions, it's difficult to tell exactly what you're trying to do. But you have a couple of options here. The function itself can access the value from the combo box if it's called while the combo box has a value in it, or the function can require the value as a function argument and whatever calls the function can pass the combo box's value.
For the first, it would look something like this:
Private Sub s13()
Dim divisor as Int32 = 1
If Int32.TryParse(Me.ComboBox1.Text, divisor) Then
' Perform your logic
Else
' The input wasn't a valid integer, maybe show an error?
End If
End Sub
Whereas the second approach might look like this:
Private Sub s13(ByVal divisor as Integer)
' Perform your logic
End Sub
And the code which calls that would need to get the value:
Dim divisor as Int32 = 1
If Int32.TryParse(Me.ComboBox1.Text, divisor) Then
s13(divisor)
Else
' The input wasn't a valid integer, maybe show an error?
End If
The main thing to note in all of this is that you should use Int32.TryParse() to determine if the inputted value in the combo box is actually an integer, and handle the error condition when it isn't.

Answer 2

You have to use the selected item :
If Int32.TryParse(ComboBox1.selectedItem, divisor) Then
MsgBox(ComboBox1.selectedItem)
Else
MsgBox("error" & ComboBox1.selectedItem)
End If

Answer 3

for anybody stuck with the same problem, here is the solution.
the code i had to work with is mammoth, so it would not let me pull in a combobox variable into any of the subs, esp as this is a multi-threaded prog. i knew, however, the solution had to be simple. and that is always something to keep in mind -- the solution is never that complicated, and you never need as much code as you think.
in this case i went down the path of a public variable,
Public Shared divisor As Integer
i placed this line underneath the very first line
Public Class frmMain
since there were other drop-down lists on the form that were clearly being drawn from, i went to the code associated with the button that initiated the steps to get the data from the server, just another button_click sub
if that sub pulled in the other combo boxes, then it had to grab the data in the one i wanted. all i did then was add this line of code to that button_click sub
divisor = ComboBox1.Text
since divisor is now a public variable, what was recorded in the button_click sub easily passes to another private sub that runs other routines. so anywhere in the code i want to use the variable 'divisor' all i have to do is mention it :)
if divisor > 0 then
'do something
end if