Visual Basic

public class form1
   inherits system.windows.forms.form

'initialization code

private m_productCode as String

friend property ProductCode() as String
   Get
      return me.m_productCode
   End Get
   Set(byval value as string)
      me.m_productcode = value
   End Set
end property

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

   me.ProductCode = textbox1.text.substring(0, 4)

   dim frmTwo as new form2
   frmTwo.FormOne = me
   frmTwo.Show

end sub

end class

*'--- in a separate code file ---'*

class form2
   Inherits System.Windows.Forms.Form

private m_formOne as Windows.Forms.Form

Friend Property Form1 as Windows.Forms.Form
   Get
      return me.m_formOne
   End Get
   Set(byval value as Windows.Forms.Form)
      me.m_formOne = value
   End Set
End Property

Private Sub form2_Load(byval sender as object, byval e as system.eventargs) handles form2.Load

'--- this line gives you access to the product code from form1 ---'
dim productCode as string = me.FormOne.ProductCode

End Sub

end class