Вызов метода пользовательских элементов управления из другой формы

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I want to call method from Usercontrol in form the method(showlistbox) is to fill the products in listbox, when the user update or delete a product I want to call the method so it will update the listbox that contains the product in the usercontrol.

I have 2 forms main form that have 'usercontrol' the 'usercontrol' have listbox and other controls, I'm using method called 'showlistbox' display the products in the listbox, if the user double click on any product in listbox this will open new form contains the product details, so if the user delete or update the product i want the listbox in the 'usercontrol' also update or refresh by calling the ' showlistbox' method.

i tried this but it show me this error : the connectionstring property has not been initialized

this is the code:

Что я уже пробовал:

dim m_product as new products
m_product.showlistbox()
And this is the showlistbox method:

Public Sub showlistbox()
    Try
        'فحص الاتصال بقاعدة البيانات
        If SQL.conn.State = ConnectionState.Open Then
            SQL.conn.Close()
        End If
        SQL.conn.Open()
        Dim dt As New DataTable
        Dim ds As New DataSet
        ds.Tables.Add(dt)
        Dim da As New SqlDataAdapter("select pname from products where not esection= N'archive' order by date DESC", SQL.conn)
        da.Fill(dt)
        Dim myRow As DataRow
        For Each myRow In dt.Rows
            ListBox1.Items.Add(myRow.Item(0)).ToString()
        Next
        SQL.conn.Close()
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub

but its not working, how can i done it?

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