calling a function from a form into a module - vb.net

Question

I have a an array in my module, so I want to display the contents of my array in a form textbox, here is my array
Module Module1
Sub AddCourse()
Dim Subjects() = {"Ms Office 2007", "internet and commmunications", "Lifetime skills"}
For i = 0 To UBound(Subjects) ' FOR LOOP TO WRITE AN ARRAY
i = i +1
Subjects(i)
Next
txtComputer.Text = subjects()
my problem is, when I try to use my texbox txtComputer in my module I get an error.
My question is, how do I make a form textbox to be used in a module
I get an error that reads "Error'txtComputer' is not declared. It may be inaccessible due to its protection level."
My question is based on, how do I get this error fixed?

Answer 1

There are several suggestions I have for you.
First, don't use UBound. That's an old VB6 function that is only provided for backwards compatability. You should instead use Subjects.Length.
Next, when you're incrementing the i variable, you don't need to say i = i + 1. You can just use the += operator for that (e.g. i += 1).
However, you shouldn't be explicitly incrementing i inside your For loop, anyway. The loop automatically increments the variable for you each time it iterates through the loop. If you do it explicitly yourself inside the loop, like that, it will skip every other item.
Next, in this case, you really should just use a For Each loop, rather than an iterator:
For Each subject As String in Subjects
'...
Next
Next, you aren't actually concatenating the items together inside you loop. You should be doing something like this:
For Each subject As String in Subjects
txtComputer.Text += subject
Next
However, in that case, for efficiency sake, you really ought to use a StringBuilder, like this:
Dim builder As New StringBuilder()
For Each subject As String in Subjects
builder.Append(subject)
Next
txtComputer.Text = builder.ToString()
But, all of this is moot because all you really need to do is to call String.Join:
txtComputer.Text = String.Join(", ", Subject)
As far as why you can't access the text box from the module, that is because the module is a separate object, so the text box is entirely out of scope. For instance, what if you had two instances of your form displayed at the same time? How in the world would this module know which form's text box you were referring to? The simplest way to correct that would be to pass a reference to your form into the module's method, like this:
Module Module1
Sub AddCourse(f As MyFormName)
f.txtComputer.Text = "Hello world"
End Sub
End Module
And then you could call it from the form, like this:
AddCourse(Me)
However, that would be exceptionally bad practice. Ideally, nothing outside of the form's code should ever deal directly with any of the controls on the form. So, the far better way to do it would be to simply have the method return the data, and then have the form set it's own control to the data that is returned, for instance:
Module Module1
Function GetCourse() As String
Return "Hello world"
End Function
End Module
And then call it from the form like this:
txtComputer.Text = GetCourse()

Answer 2

You can use String.Join to create a string which separates each subject with Environment.NewLine:
txtComputer.Text = String.Join(Environment.NewLine, Subjects)
The problem with your for loop is that it makes no sense at all since you have already declared and initialized the array in one line.
If you want to use a loop anyway, you can use a StringBuilder to concat all strings together:
Dim subjectBuilder = New System.Text.StringBuilder
For Each subject In Subjects
subjectBuilder.Append(subject).Append(Environment.NewLine)
Next
If subjectBuilder.Length <> 0 Then subjectBuilder.Length -= Environment.NewLine.Length
txtComputer.Text = subjectBuilder.ToString()