vb.net Public Shared String loose value when open second form

Question

I'm declaring two strings into my main form this way:

Public Shared SerNum As String = vbNullString
Public Shared SKey As String = vbNullString

Then I give some values to them. After that, I open another form and I try to get values from the two variables but only SerNum preserves his value while SKey turns out to be Nothing .

I repeatedly checked my code but I didn't found a reason for this to happen.
The second form is showed immediatly after giving values.
What can I check to find the error?

At the moment I solved by using a Public Shared Dictionary(of String, String) and putting both strings into it, but I would like to understand where I'm wrong.

EDIT
I found the mistake: SKey was also declared into my sub so the value wasn't assigned to the Public Shared variable but to the local variable .
I thought I had 'commented' that row...

Answer 1

I have a proposition for acceding to your variable from other form : In From main let's name it "From1" must be like :

Public Class Form1
    Public SerNum As String = vbNullString
    Public SKey As String = vbNullString


    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim fr As New Form2(Me)
        SerNum = "ValueNum"
        SKey = "ValueKey"
        fr.Show()
    End Sub
End Class

In your seconde from "Form2" :

Public Class Form2
    Dim fr As New Form1
    Public Sub New(fr As Form1)
        InitializeComponent()
        Me.fr = fr
    End Sub

    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        MsgBox(fr.SKey)
        MsgBox(fr.SerNum)
     End Sub