Hello,

So my question is that I have 2 list boxes in two forms aside from the main one. and I am trying to transfer what I choose in the side form to transfer to the list box.

several questions:
Why does the blank list form I have in the main form create a problem when I enter a name for the list box and why does it appear in the box when I put it there? As you can see in my errors. It doesn't seem to recognize the listbox that I wanted to leave empty in the main form.

Second question is how do I get names to add in the main form list box. I believe I have the right code but I seem to be missing something else as well. I want the names to display in the main list box and the integers to add up together so I can separately figure the tax and shipping myself. Thank you

Here are some pictures and codes

Main:

Print:

Audio:



Code:
Public Class MainForm

    Dim frmAudioBooks As New AudioBooks
    Dim frmPrintedBooks As New PrintedBooks
    Const decTaxRate As Decimal = 0.06D ' Tax rate for Books
    Const decShipping As Decimal = 2D ' Shipping Rate per Book
    Const decPrintIDidIt As Decimal = 11.95D 'Price of Print Book "I Did It Your Way"
    Const decPrintHistory As Decimal = 14.5D 'Price of Print Book "The History of Scotland"
    Const decPrintCalculus As Decimal = 29.95D 'Price of Print Book "Learn Calculus in One Day"
    Const decPrintStress As Decimal = 18.5D 'Price of Print Book "Feel the Stress"
    Const decAudioCaluclus As Decimal = 29.95D 'Price of Audio Book "Learn Calculus in One Day"
    Const decAudioHistory As Decimal = 14.5D 'Price of Audio Book "The History of Scotland" 
    Const decAudioScience As Decimal = 12.95D 'Price of Audio Book "The Science of Body Language"
    Const decAudioRelax As Decimal = 11.5D 'Price of Audio Book "Relaxation Techniques


    Private Sub mnuFileExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles mnuFileExit.Click
        'Close the Form
        Me.Close()
    End Sub

    Private Sub mnuHelpAbout_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles mnuHelpAbout.Click
        'Display a short description of the program
        MessageBox.Show("The program executes a shopping menu for the user to choose from many books both audio and printed and let's them pick from multiple books to check and buy. Designed by Justin Guan")
    End Sub

    Private Sub mnuProductsPrintedBooks_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles mnuProductsPrintedBooks.Click
        frmPrintedBooks.Show()
    End Sub

    Private Sub mnuProductsAudioBooks_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles mnuProductsAudioBooks.Click
        frmAudioBooks.Show()
    End Sub

    Private Sub mnuFileReset_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles mnuFileReset.Click
        lstProducts.Items.Clear()
    End Sub

End Class

Public Class PrintedBooks

    Private Sub btnPrintAddCart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrintAddCart.Click
        Dim intPrintInput As Integer 'Holds the selected Printed Book

        For intPrintInput = 0 To lstPrint.Items.Count = -1
            If lstPrint.SelectedIndex = -1 Then
                'No book is selected
                MessageBox.Show("Select a book.")
            ElseIf lstPrint.GetSelected(intPrintInput) Then
                lstProducts.Items.Add(lstPrint.Items(intPrintInput))
                'Gets the Selected book
            End If
        Next

    End Sub
End Class

Public Class AudioBooks
    Private Sub btnAudioClose_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAudioClose.Click
        Me.Close()
    End Sub

    Private Sub btnAudioAddCart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAudioAddCart.Click
        Dim intAudioInput As Integer 'Holds the selected Printed Book

        For intAudioInput = 0 To lstAudio.Items.Count = -1
            If lstAudio.SelectedIndex = -1 Then
                'No book is selected
                MessageBox.Show("Select a book.")
            ElseIf lstAudio.GetSelected(intAudioInput) Then
                lstProducts().Items.Add(lstAudio.Items(intAudioInput))
                'Gets the Selected book
            End If
        Next
    End Sub

End Class